Computational Physics

ABSTRACT The FT-IR and FT Raman spectra of 3,4-dichlorobenzaldehyde (DCB) and 4-methoxy- 3-methyl benzaldehyde (MMB) molecules have been recorded in the region 4000-400cm-1 and 3500-50cm-1 respectively. Optimized geometrical parameters, harmonic vibrational frequencies and depolarization ratio have been computed by density functional theory (DFT) using B3LYP/6-311+G(d,p) and B3LYP/6-311++G(d,p) method and basis sets. The observed FT-IR and FT-Raman vibrational frequencies are analysed and compared with theoretically predicted vibrational frequencies. The geometries and normal modes of vibration obtained from DFT method are in good agreement with the experimental data. The first-order hyperpolarizability (?0) of the investigated molecule were computed using DFT calculations. The calculated HOMO and LUMO energies shows that charge transfer occur within molecule. Unambiguous vibrational assignments of all the fundamentals was made using the total energy distribution (TED). Keywords: DCB,MMB, FT-IR, FT- Raman, HOMO-LUMO, DFT , NLO Corresponding author: mobile: +91 9442959222. E-mail address: jjmarivu@yahoo.co.in (M. Arivazhagan)

Fourier transform infrared and Fourier transform Raman spectra of 3, 5 dihydroxynaphthalene-2-carboxylicacid were recorded in the regions 4000–450 cm?1 and 3500–100 cm?1, respectively in the solid phase. The vibrational frequencies were calculated by density functional B3LYP methods with ccPVDZ and 6-31+G(d) basis sets, using Gaussian 09W program package. A detailed interpretation of the infrared and Raman spectra of 3, 5 dihydroxynaphthalene-2-carboxylicacid is reported. The thermodynamic functions of the title compound were also studied by the above methods and the basis set. The stability of the molecule arising from hyper conjugative interactions and accompanying charge delocalization has been analyzed using natural bond orbital (NBO) analysis. The HOMO and LUMO energy gap reflects the chemical activity of the molecule. The observed and calculated wave numbers are found to be in good agreement.

The FT-IR and FT-Raman spectra of 3-amino-2-bromo pyridine(ABP) were recorded in the regions 4000-400 cm-1 and 4000-100 cm-1. The fundamental vibrational frequencies and intensity of vibrational bands were evaluated using density functional theory (DFT) and standard B3LYP/6-311+G** basis set combination. The vibrational spectra were interpreted, with the aid of normal coordinate analysis based on a scaled quantum mechanical (SQM) force field. The Infrared and Raman spectra were also predicted from the calculated intensities. Comparison of simulated spectra with the experimental spectra provides important information about the ability of the computational method to describe the vibrational modes. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).

In this work, the experimental and theoretical study on vibrational spectra of 2,5-Dichloroaniline (25DCA) were studied. 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 density functional theory (DFT) using B3LYP method with 6-311+G** basis set combination. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FT-IR and FT Raman data. Simulated FTIR and FT Raman spectra for 25DCA showed good agreement with the observed spectra. Mulliken analysis of atomic charges is also calculated. The calculated HOMO–LUMO energies shows that charge transfer occur within the molecule. The dipole moment (?) and First-order hyperpolarizability (?0) of the molecule have been reported. Electronic excitation energies, oscillator strength and nature of the respective excited states were calculated by the closed-shell singlet calculation method for the molecule.

The Fourier transform Infrared (FT-IR) and FT-Raman spectra of 2-Methoxynaphthalene (2MN) have been measured. The molecular geometry, vibrational frequencies, Infrared intensities and Raman activities have been calculated by using density functional theory calculation (B3LYP) with 6-311+G** basis set. Complete vibrational assignment and analysis of the fundamental modes of the compound were carried out using the observed FT-IR and FT-Raman. Simulated FT-IR and FT-Raman spectra for 2MN showed good agreement with the observed spectra. The stability of the molecule arising from hyper conjugative interactions and the charge delocalization has been analyzed using natural bond (NBO) analysis. Further, density functional theory (DFT) combined with quantum chemical calculations to determine the first-order hyperpolarizability. The calculated HOMO and LUMO energies show that charge transfer occurs within the molecule. 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.