Computational Physics

The infrared and Raman spectra of valine and Leucine molecules have been recorded in nujall mull in the range 4000-400 cm^-1 . Large number of bands belonging to different modes of vibration could be observed and assigned. The electronic absorption spectra of these molecules have also been measured at different pH values. It is observed that absorption peak shifts with the change in pH value of the solutions. A tentative explanation of the peak shift is given.

The present investigation is aimed at the experimental and theoretical studies on molecular structure, vibration spectra of Acetone Thiosemicarbazone (C4H9N3S) were studied The FT-IR and FT-Raman spectra was recorded. The molecular geometry and vibrational frequencies of the ground state were calculated by using Hartee-Fock and Density functional methods (B3LYP) with6-311, 6-311++G(d,p)basis sets. Comparison of the observed fundamental vibrational frequencies of Acetone Thiosemicarbazone by HF and DFT method. The electric dipole moment (?) and the first hyperpolarizability (?) values of the investigated molecule were also computed.

The FT-IR, FT-Raman spectra of 1(4-nitrophenyl)ethanone (NPE) were recorded in the region 4000-400 cm-1 and 4000-100 cm-1 and analyzed. Optimized molecular structure, vibrational wavenumbers, corresponding assignments regarding NPE has become screened tentatively as well as hypothetically using Gaussian 09 program package. The geometrical parameters of the title compound are in agreement with the experimental data. Natural bonding orbital (NBO) assessment has been completed with a reason to clarify charge transfer or conjugative interaction, the intramolecular re-hybridization and delocalization of electron density within the molecule. From the MEP analysis, it is clear that the negative electrostatic potential regions are mainly localized over carbonyl group and phenyl ring are possible sites for electrophilic attack and the positive regions are localized at all the hydrogen atoms, indicating possible sites for nucleophilic attack. Local reactivity properties have been investigated using quantum chemical parameters and Fukui function analysis. The first and second-order hyperpolarizabilities were calculated. The calculated first order hyperpolarizability is commensurate with the documented worth of very similar derivatives and could be an interesting object for more experiment on nonlinear optics. The HOMO and LUMO energies also confirm that charge transfer occurs within the molecule. The NMR spectral assessment had been made choosing structure-property relationship by chemical shifts along with the magnetic shielding effects regarding the title compound. The magnetic susceptibility and thermodynamic property of the title compound for various temperatures also be discussed.

The FT-IR and FT-Raman spectra of 3-hydroxy benzylidyne trifluoride(3HBT) have been recorded in the range of 4000–400 cm-1 and 3500–50 cm-1 respectively. The molecular geometry and vibrational frequencies in the ground state are calculated using the B3LYP method with 6-311+G(d, p) and 6-311++G (d, p) basis sets. The computed values of frequencies are scaled using a suitable scale factor to yield good coherence with the observed values. Most of the modes have wave numbers in the expected range. The calculated HOMO–LUMO energy gap shows that charge transfer occur within the molecule. NBO analysis has been performed in order to elucidate charge transfers or conjugative interaction, the intra-molecule hybridization and delocalization of electron density within the molecule. The total energy distribution (TED) has also been calculated for each mode of the vibration of the molecule. Key words : FTIR, FT Raman, 3HBT, DFT, HOMO-LUMO, NBO.

The mineralogical analysis of five pottery shards from the Kottapuram site, Kerala using interdisciplinary analytical techniques such as Fourier Transform Infrared (FT-IR), XRD, thermal analysis and porosity has been carried out. The above techniques show the clear presence of inclusions of clay minerals were used for the study of characteristic reactions, associated with the course of heating. The evidence for the decomposition of calcite and kaolinite in some of the samples were found so that the earthenware may be produced the high temperature ceramics.

This work deals with the vibrational spectroscopy of 4-Fluoro-2-Nitroanisole by means of quantum chemical calculations. The FTIR and FT-Raman spectra were measured in the condensed state. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) with the standard B3LYP / 6-311+G** basis set combinations, and was scaled using various scale factors which yields a good agreement between observed and calculated frequencies. The vibrational spectra were interpreted with the aid of normal coordinate analysis based on scaled quantum mechanical force field. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra.

The FTIR and FT-Raman spectra of 2-Chloro-1-Fluoro-4-Nitrobenzene (CFNB) and 2,4-Dibromo-1-Fluorobenzene (DBFB) have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1, respectively. The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional theory (DFT) employing B3LYP 6-311++G and 6-311++G(d,p) basis set. The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibration were assigned on the basis of total energy distribution (TED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method.

The FTIR and FT-Raman spectra of 5-bromo-o-anisaldehyde (BOA) and 3-fluoro-p-anisaldehyde (FPA)have been recorded in the region 4000-400 cm-1 and 3500-50 cm-1, respectively.The structural and spectroscopic data of the molecule in the ground state were calculated by using density functional theory (DFT) employing B3LYP 6-31+G(d,p) basis set.The geometry of the molecule was fully optimized, vibrational spectra were calculated and fundamental vibration were assigned on the basis of potential energy distribution (TED) of the vibrational modes calculated with scaled quantum mechanical (SQM) method.

The molecular vibrations of 3,5-dimethylpyridine (35DMP) were investigated at room temperature by Fourier transform infrared (FTIR) and FT-Raman spectroscopy. The spectra of the above compounds have been recorded in the region 4000-400, 4000–100 cm-1, respectively. They were interpreted with the aid of normal coordinate analysis following full structure optimization and force field calculations based on density functional theory (DFT) using B3LYP /6-31G* and B3LYP/6-311+G** methods and basis set combinations. The results of the calculations were applied to simulated infrared and Raman spectra of the title compound, which showed excellent agreement with the observed spectra. The vibrational force constants were also performed by using DFT calculations. The difference between the observed and scaled wavenumber values of most of the fundamentals is very small. The values of the total dipole moment (µ) and the first-order hyperpolarizability (?) of the investigated compound were computed using DFT calculations. The calculated results also show that the 35DMP might have microscopic nonlinear optical (NLO) behavior with non-zero values. A detailed interpretation of the infrared and Raman spectra of 35DMP is also reported based on total energy distribution (TED). Electronic excitation energies, oscillator strength and nature of the respective excited states were calculated by the closed-shell singlet calculation method were also calculated for the molecule.

In this work, the vibrational spectral analysis is carried out using FTIR and FT Raman spectroscopy in the range 400-4000cm-1 and 50-3500 cm-1, respectively, for the molecule 2-6-dichlorobenzyl chloride. The molecular structure, fundamental vibrational frequencies and intensity of the vibrational bands are interpreted with the aid of structure optimizations and normal coordinate force field calculations based on HF and DFT methods with 3-21 + G basis set. The complete vibrational assignment for different normal modes of the molecule is done. Mulliken population analysis, charge distributions, thermodynamic properties and HOMO-LUMO are also discussed. With the help of specific scaling procedure, an excellent agreement between observed and calculated frequencies has been made.