Computational Physics

The solid phase FT-IR and FT-Raman spectra of pyridine-2,6-dicarbonyl dichloride (PDD) have been recorded in the regions 4000-400 cm^-1 and 3500-100 cm^-1, respectively. Geometry and vibrational wavenumbers are calculated using ab-initio Hartree-Fock (HF) and Density Functional Theory (DFT) methods employing the 6-311+G (d,p) basis set. The observed FT-IR and FT-Raman vibrational frequencies have been analyzed and assigned to different normal modes of the molecule. Using PEDs, the contributions are determined for different modes to each wavenumber.

The molecular vibrations of O-Bromobenzoyl chloride (OBBC) were investigated in polycrystalline sample, at room temperature, by Fourier transform infrared (FT-IR) and FT-Raman spectroscopies. In parallel, ab initio and various density functional (DFT) methods were used to determine the geometrical, energetic and vibrational characteristics of OBBC. On the basis of B3LYP/6-31G* and B3LYP/6-311+G** methods and basis set combinations, a normal mode analysis was performed to assign the various fundamental frequencies according to the total energy distribution (TED). Simulation of Infrared and Raman spectra, utilizing the results of these calculations led to excellent overall agreement with observed spectral patterns. The scaled quantum mechanical (SQM) approach applying selective scaling of the DFT force fields was shown to be superior to the scaling method in its ability to ensure correct band assignments and successful simulation of IR and Raman spectra including band polarizations and intensity patterns.

In the present study, the FT-IR and FT-Raman spectra of 2,4-dimethoxybenzonitrile have been recorded in the region 4000–400 cm_1 and 3500–50 cm_1, respectively. The fundamental modes of vibrational frequencies of (24DMBN) are assigned. Theoretical information on the optimized geometry, harmonic vibrational frequencies, infrared and Raman intensities were obtained by means of ab initio Hartree–Fock (HF) and density functional theory (DFT) gradient calculations with complete relaxation in the potential energy surface using 6-311++G(d,p)) basis set. The vibrational frequencies which were determined experimentally from the spectral data are compared with those obtained theoretically from ab initio and DFT calculations. A close agreement was achieved between the observed and calculated frequencies by refinement of the scale factors. The infrared and Raman spectra were also predicted from the calculated intensities. Thermodynamic properties like entropy, heat capacity, zero point energy, have been calculated for the molecule. The calculated HOMO–LUMO energy gap reveals that charge transfer occurs within the molecule. Unambiguous vibrational assignment of all the fundamentals was made using the total energy distribution (TED).

The simple 4D- hyperchaotic dynamics of an autonomous oscillator circuit was studied by measuring its responsible in the form of phase-portrait, power spectrum and hyperchaotic time series. The circuit consists of just four linear elements (two capacitors and two inductors), one linear negative conductance and two ideal diodes. The power spectrums are presented to confirm the strong hyperchaotic nature of the oscillations of the circuit. The performance of the circuit is investigated by means of experimental and numerical confirmation of the appropriate differential equations. The features of the obtained results are respected for various engineering system such as chaos based secure communication systems with robustness against various interferences.

The vibrational spectroscopy of 2-Hydroxy-6-methyl-5-Nitropyridine (HMNP) by means of quantum chemical calculation has been studied. The FT-Raman and FT-IR spectra of HMNP have been recorded in the region 3500-50cm-1 and 4000-400cm-1 respectively. The fundamental vibrational frequencies and intensity of vibrational bands have been evaluated using density functional theory (DFT) with standard B3LYP/6-311+G (d,p) basis set combinations for optimized geometries. The observed FT-IR and FT-Raman vibrational frequencies have been anlaysed and compared with theoretically predicted vibrational frequencies. The assignments of bands to various normal modes of molecule have also been carried out. The electric dipole moment (?) and the first hyper polarazibility (?) values of the investigated molecule have been computed using DFT calculations. The calculated HOMO and LUMO energies show that charge transfer occur with in the molecule.

The simple third-order chaotic dynamics of a new autonomous oscillator circuit was studied by measuring its responsible in the form of phase-portrait, power spectrum and chaotic time series. The circuit consists of just three linear elements (two capacitors and one inductor), one linear negative conductance and cubic nonlinearity exhibiting the symmetrical piecewise-linear v-i characteristics. The power spectrums are presented to confirm the lower dimensions of strong chaotic nature of the oscillations of the circuit. The performance of the circuit is investigated by means of experimental and numerical confirmation of the appropriate differential equations. The features of the obtained results are respected for various engineering system such as chaos communication systems with robustness against various interferences.

The FT-IR and FT-Raman spectra of P-Chloroaniline (PCA) have been recorded and analyzed. The optimized geometry, and harmonic vibrational wave numbers of PCA have been investigated with the help of B3LYP scaled quantum mechanical (SQM) method supplemented with 6-311++G** basis set. The infrared and Raman spectra were predicted theoretically from the calculated intensities. The observed and simulated spectra were found to be well comparable. In the investigation, we adopted density functional theory (DFT) combined with quantum chemical calculations to determine the first-order hyperpolarizability.

This work presents the quantum chemical calculations and spectral techniques of 4, 5- Diphenylimidazole (DPI). The spectroscopic properties were investigated by FT-IR and FT-Raman. The FT-IR spectrum (4000–400 cm?1) and FT-Raman spectrum (3500–100 cm?1) in solid phase was recorded for DPI. The optimised geometry, harmonic vibrational frequencies have been investigated by DFT/B3LYP method with 6-31G (d) and 6-311G (d, p) basis sets. The difference between the observed and scaled wave number values of most of the fundamental is very small. Stability of the molecule arising from hyper conjugative interactions, charge delocalization has been analyzed using natural bond orbital (NBO) analysis. HOMO and LOMO energies were measured. The electric dipole moment (?D) and first hyperpolarizability (?tot) values of the investigated molecule were computed using ab initio quantum mechanical calculations. The calculated results also show that the DPI molecule may have microscopic nonlinear optics (NLO) behavior. Finally molecular electrostatic potential (MEP) also performed.

Primarily, the vibrational spectroscopic signature of 4-chloro-3-(trifluoromethyl)aniline has been studied experimentally by means of FT-IR and FT-Raman techniques. The electron donating and electron withdrawing effects on the structure of aniline and effects of substituent positions on the vibrational spectra of the title molecule in comparison with similar kind of molecules have also been illustrated. The details about hyperconjugative interactions, HOMO-LUMO energy gap, and molecular electrostatic potential (MEP) surface analysis have been predicted with the help of theoretical density functional theory computations.

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)