Have you ever felt the sun&#;s gentle embrace on a warm day? This natural warmth that radiates through your bones is the phenomenon that is Infrared.
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In this comprehensive blog post, we will walk you through everything you need to know about infrared heating systems. From the advantages and disadvantages to frequently asked questions, our goal is to provide you with all the information necessary to make an informed decision when choosing your next heating system.
Infrared heating may seem like new technology, but it has been a trusted and efficient heating solution for decades across cleaner, environmentally-conscious countries like Austria and Switzerland. It&#;s us in the UK that have some catching up to do when it comes to adopting modern, low carbon heating systems. Join us as we explore the future of home and business heating with infrared technology. Infrared heating is gaining popularity as an efficient and effective way to heat homes and spaces. But how exactly does it work, and what makes it different from traditional heating methods? Let&#;s dive into the basics of infrared heating to understand its mechanics and benefits.
Infrared heating works on the principle of electromagnetic waves, specifically in the infrared spectrum. Unlike traditional heating systems that heat the air to warm a space, infrared heaters emit infrared radiation that directly heats objects and surfaces within their line of sight. This radiant heat is similar to the warmth you feel from the sun, minus the harmful ultraviolet rays.
Radiant Heat Infrared heaters use a filament or element that gets heated up when electricity passes through it. This element emits infrared radiation, which travels through the air and heats solid objects it comes into contact with. These objects then re-radiate heat back into the room, creating a comfortable and even warmth. Unlike conventional heaters that can waste energy by heating the air, which then rises and escapes, infrared heaters provide instant warmth without warming the air excessively. This targeted heating reduces energy consumption and can lead to lower heating bills.
Near and far infrared technologies are very different, each with its own unique strengths. Near infrared, exemplified by those glowing red/orange bar heaters often seen in outdoor settings, emits electromagnetic radiation that heats objects directly, providing immediate comfort in localised areas. Meanwhile, far infrared, the sophisticated technology powering IR heating panels, operates within a longer wavelength spectrum, gently penetrating surfaces to create a more uniform, consistent warmth throughout the space.
Far infrared&#;s ability to penetrate deeper into objects means it doesn&#;t just warm the air, it heats the objects and surfaces in the room, including walls, floors, and furniture. This not only creates a cozy environment but also helps maintain a more stable temperature, reducing energy consumption and promoting greater efficiency.
When considering heating solutions for your home or business, infrared heating is an option worth exploring. Here are several reasons why infrared heating might be a good choice:
Infrared Heating has a number of factors that make it a potentially good idea for your home. Infrared heaters are known for their high energy efficiency. They convert almost all the electricity they use into heat. Traditional heating systems often lose a significant amount of energy while warming the air, whereas infrared heaters directly warm people and objects. This targeted heating approach can reduce energy waste and potentially lower energy bills. This can be particularly advantageous in spaces with high ceilings or poor insulation, where conventional heating might struggle to maintain a uniform temperature.
Other key advantages of infrared heating include Its sleek, space-saving design which allows for versatile installation options, including ceiling and wall mounting, ensuring it fits seamlessly into any room. Custom image infrared panels and mirrored infrared panels provide aesthetic flexibility to match any décor. Additionally, infrared heating promotes a healthier environment by improving air quality and offers health benefits such as reducing blood pressure, easing muscle tension, and relieving joint pain. Furthermore, IR panels are compatible with renewable energy sources like solar, making it a sustainable heating option.
Infrared Heating has few disadvantages compared to alternative methods of heating. First of all, while it may not be considered a disadvantage, some people may prefer the overall ambient warmth of a convection heating system as this is the heat many of us are used to. Infrared heat is often likened to the feel of natural sunlight, many users do prefer this, however, strategic placement of the heating panels is important to ensure optimal heat distribution. A disadvantage of Near Infrared (NIR), exemplified by glowing red heaters you might find in outdoor areas such as restaurants and bars, is that these heaters warm people directly in their line of sight. If there are obstacles between the heater and the area to be warmed, this area may not receive sufficient heat, making strategic placement of the heaters crucial. However, this is not the technology harnessed by infrared heating panels which are an example of Far Infrared technology (FIR). These emit a more uniform and consistent heat that penetrates deeper into surfaces and objects.
Infrared Heaters are incredibly efficient and do not use much electricity compared to alternative methods of electric heating. In fact, infrared heating panels require 42% less wattage than electric convection radiators to heat an equal sized area. The direct heating method of infrared panels means that energy is used more efficiently because it targets specific areas. This means less heat is lost through ducts and ventilation. Also, unlike conventional heaters that need time to warm up the air in a room, infrared heaters deliver heat almost instantaneously, reducing the amount of time and energy needed to achieve a comfortable temperature. Furthermore, infrared heating systems allow for zoned heating, lowering overall electricity usage by not heating unoccupied rooms in your home.
Infrared heaters are inexpensive to run compared with alternative methods of heating. This is because the heat emitted by infrared panels is trapped in objects and surfaces and released over time creating a long lasting heat. These surfaces will radiate heat back into the room, long after the infrared panel has been switched off. This is a key factor in how infrared heaters keep spaces warm with minimal running costs.
The short answer is no. If used properly, Infrared heating can in fact save users money on their energy bills. Infrared heating panels are specifically engineered to provide efficient heating while keeping electricity costs in check. Unlike conventional heating methods that warm the air, infrared heaters emit infrared radiation directly to objects and surfaces within their range. This targeted approach minimises energy wastage by bypassing the need to heat the entire volume of air in a room.
Several factors influence the impact of infrared heaters on electric bills, including usage patterns and the size and insulation of the room. Employing programmable thermostats or timers can optimize energy usage by heating spaces only when needed. Additionally, properly sizing infrared heaters to match the room's dimensions and ensuring adequate insulation further enhances their efficiency and reduces operational costs.
Using an infrared heater efficiently can maximise its effectiveness and minimise energy consumption. Here are some tips to get the most out of your infrared heater:
Placement Matters Position your infrared heater in a central location where it can directly heat the objects and people in the room. Avoid placing obstacles that can block the infrared waves. We tend to find that ceiling mounted infrared panels have the most even heat distribution however, wall mounted panels still work brilliantly.
Use Zone Heating Focus on heating specific areas or zones where you spend the most time rather than trying to heat the entire building. This targeted approach can reduce energy usage and improve comfort.
Set the Right Temperature Infrared heaters heat quickly, so you can lower the thermostat of your central heating system and supplement with the infrared heater to maintain comfort. This can lead to overall energy savings.
Use Programmable Thermostats Consider using a programmable thermostat or timer to control when your infrared heater operates. This allows you to heat rooms only when they are in use, reducing unnecessary energy consumption.
Ensure Proper Insulation Good insulation in your home or office helps retain heat, allowing the infrared heater to work more efficiently. Check windows, doors, and walls for drafts and seal any gaps. Our team will assess the level of insulation in your property in order to specify the correct wattage of infrared panel to heat your room effectively.
By following these tips, you can make sure your infrared heater operates efficiently, providing comfortable warmth while keeping energy costs down.
Infrared heaters are renowned for their efficiency and effectiveness in heating spaces, but like any appliance, they can encounter occasional issues. Thankfully, unlike other heating systems, it is incredibly easy to replace Infrared heating panels with minimal or no invasive work on your home. Here are some problems than rarely occur with infrared heaters and how to address them:
Uneven Heating Sometimes, infrared heaters may not distribute heat evenly across a room. This can be due to obstacles blocking the infrared waves or improper placement. Ensure the heater is positioned centrally and without obstructions for optimal heat distribution.
Faulty Heating Elements If your infrared heater is not producing heat or is emitting insufficient warmth, it may indicate a problem with the heating elements. This could be due to wear and tear over time.
Overheating or Shutting Off Infrared heaters have built-in safety features to prevent overheating. If your heater shuts off unexpectedly, it may be due to overheating. Check for blocked vents or excessive dust accumulation, which can restrict airflow. Ensure the heater is placed in a well-ventilated area.
Electrical Issues Problems with the power supply, such as a blown fuse or tripped circuit breaker, can prevent the infrared heater from operating. Verify the power source and connections to rule out electrical issues.
Remote Control Malfunctions If your infrared heater comes with a remote control and it stops working, check the batteries first. Replace them if necessary. If the issue persists, ensure there are no obstructions between the remote and the heater's receiver.
Understanding common issues with infrared heaters allows for timely troubleshooting and maintenance, ensuring your heating system operates efficiently. These issues are incredibly rare and can be rectified easily with a simple panel replacement. All Infrared Group panels have a 40 year+ life expectancy and come with a 10 year warranty.
When considering infrared heating panels, it's essential to weigh the costs involved, including purchase, installation, and ongoing running expenses.
Infrared heating panels vary in price depending on size, brand, and features. At Infrared Group, our panels start from as little as £89.99, making them a cost-effective option for heating your home or business. Installation of infrared heating panels is generally straightforward and can often be completed by a qualified electrician in a short amount of time. This simplicity helps keep installation costs lower compared to more complex heating systems such as Gas Boilers or Air Source Heat Pumps that require extensive ductwork or plumbing adjustments. Infrared heating panels are known for their energy efficiency.
Infrared panel heaters emit infrared radiation that directly heats objects and people in the room, rather than heating the air. This targeted heating approach can result in lower running costs because less energy is wasted on heating unused spaces or circulating air. They are also unaffected by external climate unlike an ASHP which has to work harder to heat your home when the temperature outside is colder.
Many people have concerns about new technologies, especially when it comes to something as essential as heating our homes. If you&#;re curious about whether infrared heating is healthy, rest assured that infrared heating is not only safe, but also offers several health benefits. Infrared heaters emit infrared radiation, which is naturally emitted by the sun and even our own bodies. This is totally safe and isn&#;t to be confused with UltraViolet (UV) radiation, which can be harmful. All objects with a temperature above absolute zero will emit a degree of infrared radiation, so this is nothing to worry about.
As for the health benefits of infrared heaters, infrared doesn&#;t rely on heating and circulating air like forced air systems do, this means there is less spread of dust and germs and fewer allergens being stirred up. Infrared can also help to reduce damp and moisture in walls preventing mould. This is particularly beneficial for individuals with Asthma, allergies, or other respiratory conditions. In addition, infrared heat has been used in various therapeutic settings to promote better blood circulation and reduce muscle and joint pain. Furthermore, infrared heaters offer an efficient heating option that can help reduce your carbon footprint. By using less energy to provide the same level of warmth, they contribute to a greener, cleaner, healthier environment.
Infrared heaters are becoming increasingly popular for their efficiency and targeted heating capabilities. One common question among users is how long these heaters can safely be left on. Understanding the best practices for using infrared heating can help you maximise energy efficiency and enjoy the benefits of radiant warmth in your home or workspace. While infrared heaters are safe to leave on for extended periods, it's essential to follow manufacturer guidelines for optimal usage and cost effectiveness. Most infrared heaters are equipped with built-in safety features such as overheating protection and automatic shut-off mechanisms for added peace of mind.
To maximise cost-effectiveness, consider using programmable thermostats or timers with your infrared heaters. Our infrared Group panels all come with a built-in thermostat. This allows you to control when the heaters are in operation, ensuring they are only used when needed and avoiding unnecessary energy expenditure.
Adjust the thermostat settings to maintain a comfortable temperature without over-heating the space. Infrared heaters provide rapid warmth, so you may find you need to set the thermostat lower than with traditional heating systems.
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Take advantage of infrared heaters&#; ability to provide targeted heating. Focus on heating the areas you use most frequently rather than trying to maintain a uniform temperature throughout the entire property. This can lead to significant energy savings.
Once in a while wipe down your infrared panel heater with a soft, damp cloth to remove any dust build up to ensure optimal performance.
Infrared heating panels can save you space in your property due to a number of factors. Infrared panels can be mounted on ceilings or higher up on walls due to their ability to emit heat in a directional manner. This flexibility in placement allows you to maximise floor space and position furniture where you like without worrying about blocking radiators or compromising on heating efficiency. Convection radiators typically need to be positioned close to the ground to effectively warm the air, which can occupy valuable floor space and limit furniture placement. In contrast, infrared panels do not require such proximity to the floor, freeing up space for other uses.
By installing infrared panels higher up, you can achieve more even distribution of heat throughout the room. This eliminates cold spots and ensures a comfortable environment without the need for multiple heating units. Furthermore, Infrared panels come in various styles and finishes such as personalised image designs and mirrors, blending seamlessly into modern interiors. At just 22mm thick, the sleek and slim profiles contribute to a minimalist aesthetic, enhancing the overall design of your space.
Installing infrared heating panels is a straightforward process, designed to offer convenience whether you're upgrading your home or outfitting a commercial space. These panels are lightweight and versatile, allowing for installation on walls or ceilings with minimal effort. All Infrared Group panels come equipped with a 3 pin plug and a corded power supply, enabling them to be plugged directly into a standard wall socket or hardwired by a qualified electrician as per your preference.
The installation typically involves mounting the panels using provided brackets, ensuring they are securely positioned for optimal heating efficiency. Electrical connection is crucial, and we recommend hiring our team of fully qualified electricians who are adept at handling the wiring safely and in compliance with regulations. This approach not only guarantees the panels operate safely but also ensures they perform at their best.
On average, our qualified electricians can install infrared heating panels in a full three-bedroom house in just one day, minimizing disruption and ensuring you can enjoy the benefits of efficient heating quickly.
Infrared heaters offer a practical and energy-efficient solution for heating spaces effectively. By understanding how to use them correctly and efficiently, you can enjoy the benefits of radiant heat while minimizing energy costs. Whether you're heating your home, office, or commercial space, incorporating infrared heating into your heating strategy can lead to enhanced comfort and savings over time.
If you&#;re considering infrared heating for your property or have more questions about their usage and benefits, our team is here to provide expert advice and solutions tailored to your needs. Contact us today to discover how infrared heating can transform your indoor environment.
Infrared (IR) spectroscopy is one of the most common and widely used spectroscopic techniques employed mainly by inorganic and organic chemists due to its usefulness in determining structures of compounds and identifying them. Chemical compounds have different chemical properties due to the presence of different functional groups.
Infrared (IR) spectroscopy is one of the most common and widely used spectroscopic techniques. Absorbing groups in the infrared region absorb within a certain wavelength region. The absorption peaks within this region are usually sharper when compared with absorption peaks from the ultraviolet and visible regions. In this way, IR spectroscopy can be very sensitive to determination of functional groups within a sample since different functional group absorbs different particular frequency of IR radiation. Also, each molecule has a characteristic spectrum often referred to as the fingerprint. A molecule can be identified by comparing its absorption peak to a data bank of spectra. IR spectroscopy is very useful in the identification and structure analysis of a variety of substances, including both organic and inorganic compounds. It can also be used for both qualitative and quantitative analysis of complex mixtures of similar compounds.
The use of infrared spectroscopy began in the 's by Wilbur Kaye. He had designed a machine that tested the near-infrared spectrum and provided the theory to describe the results. Karl Norris started using IR Spectroscopy in the analytical world in the 's and as a result IR Spectroscopy became an accepted technique. There have been many advances in the field of IR Spec, the most notable was the application of Fourier Transformations to this technique thus creating an IR method that had higher resolution and a decrease in noise. The year this method became accepted in the field was in the late 's.4
There are three main processes by which a molecule can absorb radiation. and each of these routes involves an increase of energy that is proportional to the light absorbed. The first route occurs when absorption of radiation leads to a higher rotational energy level in a rotational transition. The second route is a vibrational transition which occurs on absorption of quantized energy. This leads to an increased vibrational energy level. The third route involves electrons of molecules being raised to a higher electron energy, which is the electronic transition. It&#;s important to state that the energy is quantized and absorption of radiation causes a molecule to move to a higher internal energy level. This is achieved by the alternating electric field of the radiation interacting with the molecule and causing a change in the movement of the molecule. There are multiple possibilities for the different possible energy levels for the various types of transitions.
The energy levels can be rated in the following order: electronic > vibrational > rotational. Each of these transitions differs by an order of magnitude. Rotational transitions occur at lower energies (longer wavelengths) and this energy is insufficient and cannot cause vibrational and electronic transitions but vibrational (near infra-red) and electronic transitions (ultraviolet region of the electromagnetic spectrum) require higher energies.
Figure 1: Energy levels for a molecule. Possible transitions that occur: (A): Pure rotational Transitions, (B) rotational-Vibrational Transitions, (C) Rotational-Vibrational-Electronic TransitionsThe energy of IR radiation is weaker than that of visible and ultraviolet radiation, and so the type of radiation produced is different. Absorption of IR radiation is typical of molecular species that have a small energy difference between the rotational and vibrational states. A criterion for IR absorption is a net change in dipole moment in a molecule as it vibrates or rotates. Using the molecule HBr as an example, the charge distribution between hydrogen and bromine is not evenly distributed since bromine is more electronegative than hydrogen and has a higher electron density. \(HBr\) thus has a large dipole moment and is thus polar. The dipole moment is determined by the magnitude of the charge difference and the distance between the two centers of charge. As the molecule vibrates, there is a fluctuation in its dipole moment; this causes a field that interacts with the electric field associated with radiation. If there is a match in frequency of the radiation and the natural vibration of the molecule, absorption occurs and this alters the amplitude of the molecular vibration. This also occurs when the rotation of asymmetric molecules around their centers results in a dipole moment change, which permits interaction with the radiation field.
Molecules such as O2, N2, Br2, do not have a changing dipole moment (amplitude nor orientation) when they undergo rotational and vibrational motions, as a result, they cannot cannot absorb IR radiation.
The absorption of IR radiation by a molecule can be likened to two atoms attached to each other by a massless spring. Considering simple diatomic molecules, only one vibration is possible. The Hook's law potential on the other hand is based on an ideal spring
\[\begin{align} F &= -kx \label{1} \\[4pt] &= -\dfrac{dV(x)}{dx} \label{2} \end{align}\]
this results in one dimensional space
\[ V(r) = \dfrac{1}{2} k(r-r_{eq})^2 \label{3}\]
One thing that the Morse and Harmonic oscillator have in common is the small displacements (\(x=r-r_{eq}\)) from the equilibrium. Solving the Schrödinger equation for the harmonic oscillator potential results in the energy levels results in
\[ E_v = \left(v+\dfrac{1}{2}\right)hv_e \label{4}\]
with \(v=0,1,2,3,...,\,infinity\)
\[ v_e = \dfrac{1}{2\pi} \sqrt{\dfrac{k}{\mu}} \label{5}\]
When calculating the energy of a diatomic molecule, factors such as anharmonicity (has a similar curve with the harmonic oscillator at low potential energies but deviates at higher energies) are considered. The energy spacing in the harmonic oscillator is equal but not so with the anharmonic oscillator. The anharmonic oscillator is a deviation from the harmonic oscillator. Other considered terms include; centrifugal stretching, vibrational and rotational interactions have to be taken into account. The energy can be expressed mathematically as
\[ E_v = \underset{\text{Harmonic Oscillator}}{\left(v+\dfrac{1}{2}\right)hv_e} - \underset{\text{anharmonicity}}{\left(v+\dfrac{1}{2}\right)^2 X_e hv_e} + \underset{\text{Rigid Rotor}}{B_e J (J+1)} - \underset{\text{centrifugal stretching}}{D_e J^2 (J+1)^2} -\alpha_e \underset{\text{rovibrational coupling}}{\left(v+\dfrac{1}{2}\right) J(J+1)} \label{6}\]
The first and third terms represent the harmonicity and rigid rotor behavior of a diatomic molecule such as HCl. The second term represents anharmonicity and the fourth term represents centrifugal stretching. The fifth term represents the interaction between the vibration and rotational interaction of the molecule.
The bond of a molecule experiences various types of vibrations and rotations. This causes the atom not to be stationary and to fluctuate continuously. Vibrational motions are defined by stretching and bending modes. These movements are easily defined for diatomic or triatomic molecules. This is not the case for large molecules due to several vibrational motions and interactions that will be experienced. When there is a continuous change in the interatomic distance along the axis of the bond between two atoms, this process is known as a stretching vibration. A change in the angle occurring between two bonds is known as a bending vibration. Four bending vibrations exist namely, wagging, twisting, rocking and scissoring. A CH2 group is used as an example to illustrate stretching and bending vibrations below.
Symmetric Stretch Asymmetric Stretch Twisting
Wagging Scissoring Rocking
Figure 3: Types of Vibrational Modes. To ensure that no center of mass motion occurs, the center atom (yellow ball) will also move. Figure from Wikipedia
As stated earlier, molecular vibrations consist of stretching and bending modes. A molecule consisting of (N) number of atoms has a total of 3N degrees of freedom, corresponding to the Cartesian coordinates of each atom in the molecule. In a non-linear molecule, 3 of these degrees of freedom are rotational, 3 are translational and the remainder is fundamental vibrations. In a linear molecule, there are 3 translational degrees of freedom and 2 are rotational. This is because in a linear molecule, all of the atoms lie on a single straight line and hence rotation about the bond axis is not possible. Mathematically the normal modes for a linear and non linear can be expressed as
Linear Molecules: (3N - 5) degrees of freedom
Non-Linear molecules: (3N - 6) degrees of freedom
Diagram of Stretching and Bending Modes for H2O.
H2O molecule is a non-linear molecule due to the uneven distribution of the electron density. O2 is more electronegative than H2 and carries a negative charge, while H has a partial positive charge. The total degrees of freedom for H2O will be 3(3)-6 = 9-6 = 3 degrees of freedom which correspond to the following stretching and bending vibrations. The vibrational modes are illustrated below:
Figure 4 The vibrational modes of H2ODiagram of Stretching and Bending Modes for CO2.
CO2 is a linear molecule and thus has the formula (3N-5). It has 4 modes of vibration (3(3)-5). CO2 has 2 stretching modes, symmetric and asymmetric. The CO2 symmetric stretch is not IR active because there is no change in dipole moment because the net dipole moments are in opposite directions and as a result, they cancel each other. In the asymmetric stretch, O atom moves away from the C atom and generates a net change in dipole moments and hence absorbs IR radiation at cm-1. The other IR absorption occurs at 666 cm-1. CO2 symmetry with \(D_{\infty h}\) CO2 has a total of four of stretching and bending modes but only two are seen. Two of its bands are degenerate and one of the vibration modes is symmetric hence it does not cause a dipole moment change because the polar directions cancel each other. The vibrational modes are illustrated below:
Figure 5 The vibrational modes of CO2The second law of Newton states that
\[F = ma\label{7}\]
where m is the mass and a is the acceleration, acceleration is a 2nd order differential equation of distance with respect to time. Thus "a" can be written as
\[a = \dfrac{d^2 y}{d t} \label{8}\]
Substituting this into Equation \ref{1} gives
\[\dfrac{m d^2 y}{d t^2}= - k y \label{9}\]
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the 2nd order differential equation of this equation is equal to \(\dfrac{-k}{m}\) displacement of mass and time can be stated as
\[y = A\cos 2 \pi \nu_m t \label{10}\]
where vm is the natural vibrational frequency and A is the maximum amplitude of the motion. On differentiating a second time the equation becomes
\(\dfrac{d^2 y}{d t^2} = - 4 \pi^2 \nu_m^2 A \cos 2 \pi \nu_m t \label{11}\)
substituting the two equations above into Newton's second law for a harmonic oscillator,
\[m*\left (-4\pi^{2}\nu_{m}^{2} A \textrm{cos }2\pi\nu_{m}t \right ) = -k * \left ( A\textrm{cos }2\pi\nu_{m}t \right ) \label{12}\]
If we cancel out the two functions \(y\),
\[4m\pi^{2}\nu_{m}^{2} = k \]
from above, we obtain the natural frequency of the oscillation.
\[\nu_m = \dfrac{1}{2\pi} \sqrt{\dfrac{k}{m}} \label{13}\]
\(\nu_m\) which is the natural frequency of the mechanical oscillator which depends on the force constant of the spring and the mass of the attached body and independent of energy imparted on the system. when there are two masses involved in the system then the mass used in the above equation becomes
\[\mu = \dfrac{m_1 m_2}{m_1+m_2} \label{14}\]
The vibrational frequency can be rewritten as
\[\nu_m = \dfrac{1}{2\pi} \sqrt{\dfrac{k}{\mu}} \label{15}\]
Using the harmonic oscillator and wave equations of quantum mechanics, the energy can be written as
\[E = \left(v+\dfrac{1}{2}\right) \dfrac{h}{2\pi} \sqrt{\dfrac{k}{\mu}} \label{16}\]
where h is Planck's constant and v is the vibrational quantum number and ranges from 0,1,2,3.... infinity.
\[E = \left(v+\dfrac{1}{2}\right)hv_m \label{17}\]
where \(\nu_m\) is the vibrational frequency. Transitions in vibrational energy levels can be brought about by absorption of radiation, provided the energy of the radiation exactly matches the difference in energy levels between the vibrational quantum states and provided the vibration causes a change in dipole moment. This can be expressed as
\[{\triangle E} = hv_m = \dfrac{h}{2\pi} \sqrt{\dfrac{k}{\mu}} \label{18}\]
At room temperature, the majority of molecules are in the ground state v = 0, from the equation above
\[E_o = \dfrac{1}{2}hv_m \label{19}\]
following the selection rule, when a molecule absorbs energy, there is a promotion to the first excited state
\[E_1 = \dfrac{3}{2} hv_m \label{20}\]
\[\left(\dfrac{3}{2} hv_m - \dfrac{1}{2} hv_m \right) = hv_m \label{21}\]
The frequency of radiation v that will bring about this change is identical to the classical vibrational frequency of the bond vm and it can be expressed as
\[E_{radiation} = hv = {\triangle E} = hv_m = \dfrac{h}{2\pi} \sqrt{\dfrac{k}{\mu}} \label{22}\]
The above equation can be modified so that the radiation can be expressed in wave numbers
\[\widetilde{\nu} = \dfrac{h}{2\pi c} \sqrt{\dfrac{k}{\mu}} \label{23}\]
where
Molecular vibrational frequencies lie in the IR region of the electromagnetic spectrum, and they can be measured using the IR technique. In IR, polychromatic light (light having different frequencies) is passed through a sample and the intensity of the transmitted light is measured at each frequency. When molecules absorb IR radiation, transitions occur from a ground vibrational state to an excited vibrational state (Figure 1).
For a molecule to be IR active there must be a change in dipole moment as a result of the vibration that occurs when IR radiation is absorbed. Dipole moment is a vector quantity and depends on the orientation of the molecule and the photon electric vector. The dipole moment changes as the bond expands and contracts. When all molecules are aligned as in a crystal and the photon vector points along a molecular axis such as z. Absorption occurs for the vibrations that displace the dipole along z. Vibrations that are totally x or y polarized would be absent. Dipole moment in a heteronuclear diatomic molecule can be described as uneven distribution of electron density between the atoms. One atom is more electronegative than the other and has a net negative charge.
The dipole moment can be expressed mathematically as
\(\mu = er \label{24}\)
The relationship between IR intensity and dipole moment is given as
\(I_{IR} \propto \left(\dfrac{d\mu}{dQ}\right)^2 \label{25}\)
relating this to intensity of the IR radiation, we have have the following equation below.
where \(\mu\) is the dipole moment and \(Q\) is the vibrational coordinate. The transition moment integral, that gives information about the probability of a transition occurring, for IR can also be written as
\(\langle \psi_ | \hat{M}| \psi_f \rangle \label{26}\)
\(i\) and \(f\) represent are initial and final states. \(\psi_i\) is the wave function. Relating this to IR intensity we have
\(I_{IR} \propto \langle \psi_ | \hat{M}| \psi_f \rangle \label{27}\)
where \(\hat{M}\) is the dipole moment and has the Cartesian coordinates, \(\hat {M_x}\),\(\hat {M_y}\), \(\hat{M_z}\). In order for a transition to occur by dipole selection rules , at least one of the integrals must be non zero.
The IR region of the electromagnetic spectrum ranges in wavelength from 2 -15 µm. Conventionally the IR region is subdivided into three regions, near IR, mid IR and far IR. Most of the IR used originates from the mid IR region. The table below indicates the IR spectral regions
Region Wavelength Wavenumbers (V), cm-1 Frequencies (v), HZ Near 0.78 -2.5 - 3.8 x - 1.2 x Middle 2.5 - 50 - 200 3.8 x - 1.2 x Far 50 -100 200 -10 3.8 x - 1.2 x Most Used 2.5 -15 -670 3.8 x - 1.2 xIR deals with the interaction between a molecule and radiation from the electromagnetic region ranging (- 40 cm-1). The cm-1 is the wave number scale and it can also be defined as 1/wavelength in cm. A linear wavenumber is often used due to its direct relationship with both frequency and energy. The frequency of the absorbed radiation causes the molecular vibrational frequency for the absorption process. The relationship is given below
\[\bar{v}(cm^{-1}) = \dfrac{1}{\lambda(\mu m)} \times 10^4 (\dfrac{\mu m}{cm}) = \dfrac{v(Hz)}{c(cm/s)} \label{28}\]
Far InfraRed Spectroscopy:
The far IR region is particularly useful for inorganic studies due to stretching and bending vibrations of bonds between the metal atoms and ligands. The frequencies, which these vibrations are observed, are usually lower than 650 cm-1. Pure rotational absorption of gases is observed in the far IR region when there is a permanent dipole moment present. Examples include H2O, O3, HCl.IR spectroscopy is a great method for identification of compounds, especially for identification of functional groups. Therefore, we can use group frequencies for structural analysis. Group frequencies are vibrations that are associated with certain functional groups. It is possible to identify a functional group of a molecule by comparing its vibrational frequency on an IR spectrum to an IR stored data bank.
Here, we take the IR spectrum of Formaldehyde for an example. Formaldehyde has a C=O functional group and C-H bond. The value obtained from the following graph can be compared to those in reference data banks stored for Formaldehyde. A molecule with a C=O stretch has an IR band which is usually found near cm-1 and around cm-1 for CH2 bend. It's important to note that this value is dependent on other functional groups present on the molecule. The higher cm-1 indicates a large dipole moment change. It is easier to bend a molecule than stretch it, hence stretching vibrations have higher frequencies and require higher energies than bending modes. The finger print region is a region from -650 cm-1. Each molecule has it's own characteristic print and is often cumbersome to attach any values to this region.
Figure 6IR Spectrum of Formaldehyde
Infrared spectroscopy can also be applied in the field of quantitative analysis, although sometimes it's not as accurate as other analytical methods, like gas chromatography and liquid chromatography. The main theory of IR quantification is Beer's law or Beer-Lambert law, which is written as
\[ A= \log \left ( \dfrac{I_0}{I} \right ) =\epsilon lc \label{29}\]
Where A is the absorbance of the sample, I is the intensity of transmitted light, I0 is the intensity of incident light, l is the path length, a is the molar absorptivity of the substance, and c is the concentration of the substance.
From the Beer's Law, we could figure out the relation between the absorbance and the concentration of the sample since the analytes have a particular molar absorptivity at a particular wavelength. Therefore, we could use IR spectroscopy and Beer's Law to find the concentration of substance or the components of mixture. This is how the IR quantification operated.
In order for vibrational transitions to occur, they are normally governed by some rules referred to as selection rules.
\(\left(\dfrac{d\mu}{dr}\right)_{r_{eq}} \not= 0 \label{30}\)
\(\triangle v = +1\) and \(\triangle J = +1 \label{31}\)
For any anharmonic oscillator, the selection rule is not followed and it follows that the change in energy becomes smaller. This results in weaker transitions called overtones, then
\(\triangle v = +2\) (first overtone) can occur, as well as the 2
ndovertone
\(\triangle v = +3\). The frequencies of the 1st and 2nd overtones provides information about the potential surface and about two to three times that of the fundamental frequency.
\(k = \left(\dfrac{d^2 V(r)}{dr^2}\right)_{r_{eq}} \label{32}\)
where k is the force constant and indicates the strength of a bond.
It's been observed that the effect on k when an atom is replaced by an isotope is negligible but it does have an effect on \(\nu\) due to changes in the new mass. This is because the reduced mass has an effect on the rotational and vibrational behavior.
Solvent Effects:
The polarity of solvent will have an influence on the IR spectra of organic compounds due to the interactions between solvent and compounds, which is called solvent effects. If we place a compound, which contains n, pi and pi* orbitals, into a polar solvent, the solvent will stabilizes these three orbitals in different extent. The stabilization effects of polar solvent on n orbital is the largest one, the next larger one is pi* orbital, and the effects on pi orbital is the smallest one. The spectra of n&#;pi* transition will shift to blue side, which means it will move to shorter wavelengths and higher energies since the polar solvent causes the energy difference between n orbital and pi* orbital to become bigger. The spectra of pi&#;pi* transition will shift to red side, which means it will move to longer wavelengths and lower energies since the polar solvent causes the energy difference between n orbital and pi* orbital to become smaller.
One of the most importance applications of IR spectroscopy is structural assignment of the molecule depending on the relationship between the molecule and observed IR absorption bands. Every molecule is corresponding to one particular symmetry point group. Then we can predict which point group the molecule is belonging to if we know its IR vibrational bands. Vice versa, we can also find out the IR active bands from the spectrum of the molecule if we know its symmetry. These are two main applications of group theory. We'll take the following problem as an example to illustrate how this works.
How do you distinguish whether the structure of transition metal complex molecule M(CO)2L4 is cis or trans by inspection of the CO stretching region of the IR spectra?
For cis-M(CO)2L4, the symmetry point group of this molecule is C2v.
C2v E C2 \({\sigma}\)(xz) \({\sigma}\)(yz) \({\gamma}\)co 2 0 2 0\({\gamma}\)co = A1 + B1
Since A1 has a basis on z axis and B1 has a basis on x axis, there are two IR vibrational bands observed in the spectrum.
For trans-M(CO)2L4, the symmetry point group of this molecule is D4h.
D4h E C4
C2 C2' C2" i S4 \({\sigma_h}\) \({\sigma_v}\) \({\sigma_d}\) \({\gamma}\)co 2 2 2 0 0 0 0 0 2 2\({\gamma}\)co = A1g + A2u
Since A2u has a basis on z axis, there is only one IR vibrational band observed in the spectrum.
Therefore, from what have been discussed above, we can distinguish these two structures based on the number of IR bands.
The frequency of C=O stretching is higher than that of C=C stretching. The Intensity of C=O stretching is stronger than that of C=C stretching. Explain it.
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