Papers by vipin bahadur singh
Journal of Molecular Modeling, 2009
The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized mo... more The FTIR spectrum of 2-nitroaniline was recorded in the regions 4000-400 cm(-1). The optimized molecular geometry, bond orders, atomic charges, harmonic vibrational wave numbers and intensities of vibrational bands of 2-nitroaniline and its cation were calculated at DFT levels invoking two different basis sets 6-31G and 6-31+G using Gaussian 03W program. The X-ray geometry and FTIR vibrational frequencies were compared with the results of DFT calculations. The thermal stability of 2NA is studied by the thermo gravimetric analysis (TGA). Experimental degradation process of 2-nitroaniline was interpreted with the bond order analysis. The Mulliken atomic charge analysis was also made in the present study. Based on the molecular geometry and Mulliken charge analysis, intra molecular hydrogen bonding was identified.
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Nature Human Behavior, 2021
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Journal of Physical and Chemical Reference Data, 2005
An extensive study of the available spectroscopic information on four gallium monohalides has bee... more An extensive study of the available spectroscopic information on four gallium monohalides has been conducted. The literature survey extends to early 2003 and the experimental and theoretical data on the molecular constants for the ground state, as well as for the excited states of these molecules, is presented. A brief discussion on the spectroscopic properties of different electronic states, ionization potentials, ground state dissociation energies, and percentage ionic character are given. The Rydberg–Klein–Rees potentials for the electronic states and centrifugal distortion constants for the observed vibrational levels for the electronic states of GaX (X=F, Cl, Br, and I) are also presented.
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Journal of Molecular Structure: THEOCHEM, 2009
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2013
Vibrational spectra and molecular structure of anhydrous caffeine have been systematically invest... more Vibrational spectra and molecular structure of anhydrous caffeine have been systematically investigated by second order Moller-Plesset (MP2) perturbation theory and density functional theory (DFT) calculations. Vibrational assignments have been made and many previous ambiguous assignments in IR and Raman spectra are amended. The calculated DFT frequencies and intensities at B3LYP/6-311++G(2d,2p) level, were found to be in better agreement with the experimental values. It was found that DFT with B3LYP functional predicts harmonic vibrational wave numbers more close to experimentally observed value when it was performed on MP2 optimized geometry rather than DFT geometry. The calculated TD-DFT vertical excitation electronic energies of the valence excited states of anhydrous caffeine are found to be in consonance to the experimental absorption peaks.
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2006
FTIR and Raman spectra of a rubber vulcanization accelerator, 2-mercaptobenzothiazole (MBT), were... more FTIR and Raman spectra of a rubber vulcanization accelerator, 2-mercaptobenzothiazole (MBT), were recorded in the solid phase. The harmonic vibrational wavenumbers, for both the toutomeric forms of MBT, as well as for its dimeric complex, have been calculated, using ab initio RHF and density functional B3LYP methods invoking different basis sets upto RHF/6-31G** and B3LYP/6-31G** and the results were compared with the experimental values. Conformational studies have been also carried out regarding its toutomeric monomer forms and its dimer form. With all the basis sets the thione form of MBT (II) is predicted to be more stable than thiol form (I) and dimeric conformation (III) is predicted to be more stable with monomeric conformations (I) and (II). Vibrational assignments have been made, and it has been found that the calculated normal mode frequencies of dimeric conformation (III) are required for the analysis of IR and Raman bands of the MBT. The predicted shift in NH- stretching vibration towards the lower wave number side with the B3LYP/6-31G** calculations for the most stable dimer form (III), is in better agreement with experimental results. The intermolecular sulfur-nitrogen distance in N-H...S hydrogen bond was found to be 3.35 angstroms from these calculations, is also in agreement to the experimental value.
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Journal of Physical and Chemical Reference Data, 2004
Page 1. Spectroscopic Studies of Diatomic Indium Halides SK Mishra, Raj KS Yadav, and VB Singha
... more Page 1. Spectroscopic Studies of Diatomic Indium Halides SK Mishra, Raj KS Yadav, and VB Singha
Department of Physics, Udai Pratap Autonomous College, Varanasi 221002, India SB Rai Department of Physics, Banaras Hindu University, Varanasi 221005, India ...
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Journal of Chemical Sciences, 2007
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Proceedings of the 71st International Symposium on Molecular Spectroscopy, 2016
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ACS chemical neuroscience, 2021
The precise determination of the neurotransmitter dopamine's conformational preferences in aq... more The precise determination of the neurotransmitter dopamine's conformational preferences in aqueous solution is crucial for understanding its neurobiological function. The first principle Møller-Plesset perturbation theory (MP2) and dispersion corrected density functional theory (DFT-D3) methods, employing the basis set aug-cc-pVDZ(/pVTZ), are used to reinvestigate the nine lowest-energy (isolated) structures of protonated dopamine (DAH+) in both gas and aqueous phases. DAH+ trans isomer t1 is found higher in energy than lowest-energy gauche isomer g+1 (g + 1) by 6.4 and 5.7 kJ mol-1, at the MP2 and B3LYP-D3 levels of theory, respectively, in the aqueous environment within the polarizable continuum model (PCM). We found that the solvated cation, NH3+, retains its attractive character, which supports the previous report that agonist DAH+ can be involved in cation (NH3+)-π interaction in the active states of the D2 dopamine receptor. The dispersion corrected DFT evaluation of anhar...
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Nature Human Behaviour
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Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy, 2006
The vibrational spectra of benzofuran and some of its derivatives have been systematically invest... more The vibrational spectra of benzofuran and some of its derivatives have been systematically investigated by ab initio and density functional B3LYP methods. The harmonic vibrational wavenumbers and intensity of vibrational bands were calculated at ab initio and DFT levels invoking different basis sets up to 6-311++g**. Vibrational assignments have been made and it has been found that the calculated DFT frequencies agree well in most cases with the observed frequencies for each molecule. Conformational studies have also been carried out and it is evident from ab initio calculations that 2(3H) benzofuranone is more stable than 3(2H) benzofuranone in support to our earlier semiempirical results.
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Ab initio potential energy surface for the gorund and first excited states of the Xe+OH complex w... more Ab initio potential energy surface for the gorund and first excited states of the Xe+OH complex were calculated using the state-averaged complete active space MCSCF (CASSCF) and multi reference Cl methods as implemented in MOLPRO 2006 program. A large one-electron basis consisting of the augmented-correlation consistent polarized valence five zeta (aug-cc-pV5Z) set is used. Interaction energies were obtained as the
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The structure, stability and vibrational characteristics of Isatin-(Water)_n clusters with n=1=3 ... more The structure, stability and vibrational characteristics of Isatin-(Water)_n clusters with n=1=3 have been investigated using second order Moller-Plesset (MP2) perturbation tehory and Density Functional Theory (with B3LYP) methods employing the basis set 6-31+G(d). The vertical excitation energies for these complexes have been also computed using the time-dependent density functional theory. The three stable conformational isomers, each for Isatin-(Water)_1 and Isatin-(Water)_2
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RSC Adv., 2015
Optimized geometry of newly characterized theophylline dimer Form IV at MP2/6-311++G(d,p) level.
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RSC Adv., 2014
Blue and red shift of the VEE of the S1 (1ππ*) state of caffeine after forming complex with water... more Blue and red shift of the VEE of the S1 (1ππ*) state of caffeine after forming complex with water at isolated and conjugated carbonyl site.
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Pramana, 1998
Fluorescence spectrum of Dy3+, Dy3+-Ho3+, Tb3+ and Tb3+-Er3+ doped in calibo glass have been stud... more Fluorescence spectrum of Dy3+, Dy3+-Ho3+, Tb3+ and Tb3+-Er3+ doped in calibo glass have been studied using Ar+ and excimer lasers. Non-radiative energy transfer from trivalent dysprosium and terbium (donors) to holmium and erbium (acceptors) respectively has been observed on the basis of decrease in the life time of the levels and reduction in fluorescence intensity of Dy3+ and Tb3+ on
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Spectrochimica Acta Part A: Molecular and Biomolecular Spectroscopy, 2002
The infrared spectrum of bilirubin has been recorded in the spectral region 200-4000 cm(-1). The ... more The infrared spectrum of bilirubin has been recorded in the spectral region 200-4000 cm(-1). The Raman spectrum has also been recorded using the second harmonic (530 nm) radiation of a 200 mW Nd-YAG laser. In order to confirm the vibrational assignment of the bands obtained from experimental observation, a normal coordinate analysis has been carried out using the semi-empirical AM1 method through MOPAC 5.1 computer program. Electronic absorption spectrum of bilirubin dissolved in CHCl3 has been recorded in the spectral region 300-600 nm. A broad spectrum is observed with peak maxima at 454.2 nm. The photoacoustic spectrum of this molecule (in the powder form) has also been recorded for the first time which shows certain discrete features.
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Physica B+C, 1987
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Papers by vipin bahadur singh