Ir Spectroscopy Lab Report

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1. Introduction to FTIR spectroscopy: IR spectroscopy was the first structural spectroscopic technique. The IR spectrometry is an analytical technique used to characterize the bonding structure of atoms based on the interaction of the IR radiation with matter, and measures the frequencies of the radiation at which the substance absorbs and lead to the production of vibrations in molecules. Vibrational spectroscopy history begins with the first infrared (IR) spectrum, obtained by Coblentz (1905), and achievement of first IR spectrometer (in 1930s). Fourier transform infrared (FTIR) spectrometery combines an old analytical method (IR spectroscopy, with an interferometer developed by Albert Michelson) with an older technique for converted the…show more content…
A substance is “infrared-active” if the electric dipole moment of the molecule may be changed during the vibration. Upon an interaction of the IR radiation with an oscillating dipole moment associated with a vibrating bond, the absorption of the radiation corresponds to a change of the dipole moment. In case of “‘infrared-inactive” molecule the dipole moment remains zero no matter how long is the bond. A polar bond is usually IR-active. A non-polar bond in a symmetrical molecule will absorb weakly or not at all. Symmetrical molecules will have fewer ‘infrared-active’ vibrations than asymmetrical molecules. This leads to the conclusion that symmetric vibrations will generally be weaker than asymmetric vibrations, since the former will not lead to a change in dipole moment. In a molecule there is different atoms connected by bonds and each of different material is a unique combination of atoms; no two compounds produce the exact same infrared spectrum, each bond has different characteristic IR absorption band. The frequencies of absorbed radiation are unique for each molecule which provides the characteristics of a substance. The frequencies and intensities of absorbed infrared light depend on the specific bond strengths and atoms of that molecule, and the absorption pattern (called a spectrum) is unique for each molecule. The condition of the material, such as the temperature, the state (solid,…show more content…
Vibrations can involve either a change in inter-atomic bond length (stretching, ν) or bond angle between two bonds (bending or deformation, δ). In the stretching mode the bonds can stretch in-phase (symmetrical stretching, νs) or out-of-phase (asymmetric stretching, νas). In the bending mode the position of the atom changes relative to the original bond axis and can be different types of bending vibrations: scissoring, (δ,ə or sr), rocking (δ,ρ), wagging(δ/w), twisting(δ/τ). Also can talk about deformation in plane (δ/β) - scissoring and rocking or deformation out of plane (δ/γ) – wagging and twisting. The symmetrical stretching mode may occur at lower wavenumbers than asymmetrical stretching mode and the bending vibration is much easier than stretching so it occurs at lower wavenumber. As a consequence of the multiplicity of bending and stretching modes, the infrared spectra get very

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