Browsing by Author "D.K. Rai"

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2S1 excitation of the helium atom
(1983) C.S. Singh; R. Srivastava; D.K. Rai
The variable-charge Coulomb-projected Born approximation proposed by Schaub-Shaver and Stauffer is used to analyze the electron-impact excitation of the 2S1 state of helium. Differential and integrated cross sections for the transition are calculated and compared with the other available theoretical calculations and experimental measurements. © 1983 The American Physical Society.
A new band system in the emission spectrum of diatomic bismuth
(1971) Jagadigh Singh; K.P.R. Nair; D.K. Rai
Several new bands lying in the region 6200A-6500A have been observed in an electrodeless discharge through BiCl3 mixed with Argon. These have been assigned to a new band system of the Bi2 molecule. The bands can be represented by the expression. [formula omitted]. © 1971, Taylor & Francis Group, LLC. All rights reserved.
A simple laser power meter dependent on photoacoustic effect
(1987) V.N. Rai; S.N. Thakur; D.K. Rai
The design and fabrication of a simple laser power meter dependent on the photoacoustic effect is described. This power meter has a sensitivity of 1 mV/3.5 mW laser power and the microphone has a sensitivity of 10 mV/Pa. It can be used in any wavelength region and its calibration is easy.
A two step optical double resonance study of a Fe-Ne hollow cathode discharge using optogalvanic detection
(1991) G. Ullas; S.B. Rai; D.K. Rai
Optogalvanic double resonance spectrum of Ne has been studied using a helium-neon laser and Ar+ laser pumped dye laser. Double resonance signals could be indentified as due to two step excitation with the same or different intermediate levels. Variation of LOG signal with the laser power, discharge voltage, discharge current and chopping frequencies has been studied. © 1991.
Ab-initio and density functional study of l- and d-forms of alanine and serine in gas phase and bulk aqueous medium
(Elsevier, 2007) D.M. Upadhyay; Amareshwar Kumar Rai; D.K. Rai; A.N. Singh; Anup Kumar
The molecular geometry of l and d-forms of alanine and serine in gas phase have been studied by using ab-initio quantum chemical calculations at the restricted Hartree-Fock (RHF) level by employing 6-31G and 6-311++G** basis sets. Subsequently, for considering the electron correlations, Density functional Calculations at the Becke3LYP (B3LYP) and Moller-Plesset second order (MP2) level of calculations have been carried out with the same basis sets for these optimized geometries. Effect of solvation in water on the optimized geometries was studied using the polarized continuum model of the self-consistent reaction field (SCRF) theory. The dipole moment, energy, polarizabilities and vibrational frequencies have been calculated in all cases. Frequency analysis was carried out to ensure that optimized geometry corresponds to a total energy minimum. © 2006 Elsevier B.V. All rights reserved.
All Valence Electron Molecular Orbital Study of Electronic Structure and Spectra of the three Isomeric Xylenes
(1972) J.S. Yadav; P.C. Mishra; D.K. Rai
The modified method of Del Bene and Jaffe1 (CNDO-CI) has been applied to study the electronic structure and spectra of the three isomeric xylenes taking a three dimensional geometry for the CH3 group. The spectral transition energies and the corresponding oscillator strengths have been computed and the results are compared with x-electron calculations and experimental results. Quite satisfactory results have been obtained. Ionization potentials have also been computed by the INDO and extended Huckel methods. © 1972 by Marcel Dekker, Inc. All Rights Reserved.
Analysis of some bands of the β system of PO
(1972) S.B. Rai; D.K. Rai; K.N. Upadhya
The rotational analysis of some bands of the beta band system of the PO molecule has been revised and some new bands, for example (1,2), (3,2), (3,4), (4,3), (4,5) and (7,8) of the subsystem B2 Sigma +-x 2 Pi 3/2 and (4,3), (5,4), (5,5) and (6,7) of the subsystem B2 Sigma +-x2 Pi 1/2 have been analysed. Perturbation in the 6th and 7th vibrational levels of the upper excited state have been investigated.
Application of classical collision theory to electron impact double ionization of atoms
(1973) B.N. Roy; D.K. Rai
The classical binary encounter theory in its symmetrical form has been applied to the double ionization of He and Li+. Process of double ionization has been assumed to proceed via double encounter. In both encounters correct quantum mechanical velocity distributions for the bound electron have been used. The results are compared with experimental observations and earlier calculations by Gryzinski's method. It is concluded that the single encounter model suggested by Mittleman (1966) is not entirely correct and substantial contributions are made by double encounter process.
Approximate SCF CI calculation of excited state geometries of phenol, aniline, para-fluorophenol and para-fluoroaniline
(1975) J.S. Yadav; P.C. Mishra; D.K. Rai
The CNDO/s method has been used to study the electronic structure, spectra, geometry and rotational constants in the ground and the first excited singlet states of phenol, aniline, para-fluorophenol and para-fluoroaniline. The ground state geometry has also been studied using CNDO/2 and INDO methods. Calculated bond length changes following the electronic excitation have been compared with experimental results and ambiguities present in the latter have been resolved. © 1974.
Ayurvedic medicine: Standardization difficulties
(2012) D.K. Rai; A.N. Singh
[No abstract available]
Binding energy of lithium halide molecules
(1975) S.B. Rai; D.K. Rai
A semi-empirical open shell model of sigma bonded systems has been employed to calculate the binding energies for diatomic lithium halides. The repulsion between the atomic cores is taken as the Coulomb repulsion term 1 R12 modified by the presence of electronic cores. This modification has been estimated from the repulsion term in the Rittner potential function. The agreement with the experimental values is quite satisfactory but the extension of the same method to alkali hydrides results in gross discrepancies. The results are discussed in the light of other results. © 1975.
Bond order–bond length relationship in all-valence-electron molecular orbital theory
(1972) P.C. Mishra; D.K. Rai
[No abstract available]
Calculation of molecular dipole moments using CNDO and INDO methods
(1972) J.S. Yadav; P.C. Mishra; D.K. Rai
[No abstract available]
Capture of hydrogen atom from HCl by a fast proton
(1987) H. Karki; C.S. Singh; D.K. Rai
Using the quantum theoretical version of the Thomas double-scattering model given by Shakeshaft and Spruch, we have obtained the collision cross sections for the reaction H++HClH2 ++Cl. © 1987 The American Physical Society.
CNDO CI study of electronic structure and geometry in ground and excited states. ortho- and meta- difluorobenzenes
(1973) J.S. Yadav; P.C. Mishra; D.K. Rai
The modified CNDO/2 method (CNDO/s) has been applied to study the electronic structure and geometry of ortho- and meta-difluorobenzenes in their ground and first excited singlet states. Calculated density matrices have been transformed into σ- and π-bond orders by the technique suggested earlier. Bond lengths have been calculated using the Coulson bond-orderbond-length relationship and the bond angles were assumed to the 120° in both states of these molecules. The calculated rotational constants are in very good agreement with the experimental measurements recently reported by Hartford and Lombardi. © 1973.
Cndo-ci study of electronic structure and molecular geometry in ground and excited states i. Monofluorobenzene and para-difluorobenzene
(1973) J.S. Yadav; P.C. Mishra; D.K. Rai
The modified CNDO method of Del Bene and Jaffe (CNDO/s) and the CNDO/2 and INDO methods due to Pople have been used to study the electronic structure and geometry of mono- and p-difluorobenzenes in the ground and the first excited singlet states. Bond orders, hybrid populations and transition energies together with the corresponding oscillator strengths have been given. Ground and excited state rotational constants and changes in bond lengths in the excited state as compared to the ground state have also been presented and discussed in the light of experimental observations. © 1973 Taylor & Francis Group, LLC.
Conformational search for zwitterionic leucine and hydrated conformers of both the canonical and zwitterionic leucine using the DFT-CPCM model
(2011) Amareshwar Kumar Rai; Xuee Xu; Zijing Lin; D.K. Rai
The stable conformations for zwitterionic leucine have been searched for in solution as well as in gas phase. A total of 54 trial structures were generated by considering possible combinations of single bond rotamers. It is observed that zwitterions are not stable in gas phase. In order to investigate the zwitterions of leucine in solution, the calculations for all trial structures of zwitterions were performed initially at the PM3 level and 14 the lowest energy structures were reoptimized at the B3LYP/6-311G(d) level using the CPCM model. Seven of these conformers of zwitterionic leucine were found to be stable in solution. The five most stable conformers were then reoptimized at the B3LYP/6-311++G(d, p) level. The energy ordering of the canonical leucine(neutral) conformers were also considered on the basis of single point energy calculations at the B3LYP/6-311++G(d, p) level using the CPCM model. The chemical hardness, chemical potential, vertical ionization energy and vertical electron affinity were calculated for a few of the most stable canonical leucine and its zwitterions in solution. The effects of explicit addition of water molecules (microsolvation) on the structure and the energy of both canonical and zwitterionic conformers of leucine were investigated. It is noted that in gas phase, the singly and doubly hydrated canonical (neutral) forms are more stable than their zwitterionic counterparts. The solvated zwitterions and canonical structures of leucine were further investigated using the discrete/SCRF model with zero, one and two water molecules. In solution, the continuum solvent model shows that the bare zwitterionic form is more stable than the bare canonical form by 1.6 kcal/mol. This energy separation is increased to 3.8 and 4.8 kcal/mol with inclusion of one and two water molecules, respectively. The optimized structural parameters for the most stable zwitterionic leucine with zero, one and two water molecules in solution were compared with those reported for l-leucine crystal, which shows a close agreement between the optimized geometrical parameters of the zwitterionic leucine with two water molecules in solution with the experimental geometrical parameters for l-leucine crystal. It is also observed that when the structures of zwitterions with one and two explicit water molecules are optimized in solution, the geometrical parameters and their relative energies are found to be appreciably modified. We have also calculated the vibrational spectra of the most stable solvated zwitterionic leucine as well as for the most stable structure of zwitterionic leucine with one and two water molecules in solution. © 2010 Elsevier B.V. All rights reserved.
Conformational studies of bacterial peptidoglycan: structure and stereochemistry of N-acetyl-β-d-glucosamine and N-acetyl-β-d-muramic acid
(1989) P.N.S. Yadav; D.K. Rai; J.S. Yadav
The energies of various conformations of N-acetyl-β-d-glucosamine (NAG) and its 3-O-d-lactic acid derivative N-acetyl-β-d-muramic acid (NAM) have been calculated by geometry optimization using the molecular mechanics program MM2. The geometries of these systems have been analyzed in the light of ring torsion, bond lengths, bond angles and conformational states of side groups of the pyranosyl ring and compared with available experimental data of similar pyranose derivatives. The present study indicates the presence of hydrogen bonds to stabilize the side group conformations. Discrepancies with experimental data that are seen in a few cases are ascribed to the nature of the side groups and their geometry. © 1989.
Cross section for double lonization by electron impact: Li+, Na-1, K+
(1971) D.N. Tripathi; D.K. Rai
The cross sections for double ionization by electronic impact on Li +, Na+, and K+ ions have been calculated using the Grysinski's semiclassical formula. Good agreement is obtained between calculated results and experiment in case of Li+, and it is expected that the results for Na+ and K+ would also be reliable. The ratio (σ+/σ++) (single ionization/double ionization) is also calculated and compared with the experimental results and theoretical predictions.
Cross sections for ionization of ions by electron impact
(1971) D.N. Tripathi; D.K. Rai
Cross sections for ionization of ions by electron impact have been calculated using various classical and empirical methods. Empirical modifications have been suggested in few known empirical formulae to improve the results. Calculated cross sections have been compared with other theoretical calculations and observed cross sections. The dependence of the ionization cross sections on ionic charge (Z) is also discussed. © 1971.