Computational Physics

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.

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.