Ftir and ft raman vibrational spectra molecular structure first hyperpolarizability and homo lumo analyses of some poly atomic molecules

Abstract

In the study of molecular dynamics, vibrational spectroscopy plays an important role in the structure elucidation and in the determination of characteristic groups. Molecules of complex nature can also be exposed to infrared and Raman radiation to observe their spectra. They have been analyzed in detail by considering symmetry properties and group theory. An infrared spectrum originates from molecular vibrations which cause a change in the dipole moment of the molecule, especially masses of the constituent atoms and the intermolecular forces acting between them. Raman spectrum arises if there is a change in polarizability during the vibration. Modern spectroscopic methods become powerful tool in the investigations of the physical, chemical thermodynamic properties and nature of Inter-atomic forces in the molecules. The vibrational spectroscopy is also useful in the identification of functional groups and the strength of the chemical bonding between atoms. The philosophy of computational methods of vibrational spectroscopy significantly changed after the introduction of quantum chemical calculations. This has opened the way for calculating the frequencies and intensities of spectral bands. The vibrational and rotational energies of the molecules can be studied by infrared and Raman spectroscopy. The infrared and Raman spectroscopic methods mostly yield complementary types of information. For a complete vibrational analysis, both methods should necessarily be used. When an infrared light passes through a sample, some of the frequencies are absorbed while other frequencies are transmitted through the sample without being absorbed. The percentage of absorption or transmission against frequencies is the resultant IR spectrum. In order to obtain Raman spectrum now-a-days, a power laser sources are used for excitation of the sample. newline