Browsing by Author "S.N. Thakur"
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PublicationLetter A dc laser pump results in an ac photoacoustic signal(1989) V.N. Rai; B.N. Singh; S.N. Thakur[No abstract available]PublicationArticle A high resolution investigation of the near ultraviolet absorption spectrum of p-fluorochlorobenzene(1969) S.N. Thakur; K.N. UpadhyaThe intense b ands in the near ultraviolet absorption spectrum of p-fluoro-chlorobenzene show regular rotational features under high resolution. Band contour analysis confirms the electronic transition to be 1B2 ← 1A1. The rotational lines have been interpreted by a prolate symmetric rotor model for the molecule. The observed rotational constants indicate that the size of the phenyl ring increases on electronic excitation. © 1969.PublicationArticle A simple laser power meter dependent on photoacoustic effect(1987) V.N. Rai; S.N. Thakur; D.K. RaiThe 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.PublicationArticle A3Π1u ← X1Σg + laser photoacoustic spectroscopy of Br2 vapor in the extreme red wavelength region 665-720 nm(2004) Ramesh C. Sharma; S.N. Thakur; K.C. LinThe A3Π1u ← X 1Σg+ photoacoustic spectrum of Br 2 vapor has been studied and vibronic analysis performed using earlier data available for this system of bands from optical spectroscopy in the region 665-720nm. The vibronic levels involved in these transitions are 4≦v′≦21 and 1≦v″≦4. The relative photoacoustic intensities of the vibronic bands have been used in estimating the non-radiative relaxation rate from vibrational levels of A3Π1u state. The non-radiative relaxation is found to be a nonlinear function of the upper state vibrational quantum number. The radiative rate constants for the A3Π1u state vibrational levels have been compared with the corresponding non-radiative constants obtained from present work. Non-radiative decay rate constants for the vibrational levels of A 3Π1u state have been experimentally determined for the first time from photoacoustic spectrum of Br2 vapor in the extreme red region. © 2003 Published by Elsevier B.V.PublicationBook Chapter PublicationArticle CO2 laser photoacoustic spectra and vibrational modes of heroin, morphine and narcotine(Indian Academy of Sciences, 2002) R.L. Prasad; S.N. Thakur; G.C. BharHeroin, morphine and narcotine are very large molecules having 50, 40 and 53 atoms respectively. Moderately high resolution photoacoustic (PA) spectra have been recorded in 9.6 μm and 10.6 μm regions of CO2 laser. It is very difficult to assign the modes of vibrations for PA bands by comparison with conventional low resolution IR spectra. The ab initio quantum chemical calculations were used for determining the molecular geometries and normal mode frequencies of vibrations of these molecules for assignments of PA spectra.PublicationArticle Compositional study of gallbladder stone using photoacoustic spectroscopy(Elsevier Ltd, 2019) Zainab Gazali; S.N. Thakur; A.K. RaiMolecular composition of gallbladder stone has been investigated for the first time by means of photoacoustic spectroscopy (PAS). The presence of cholesterol, calcium carbonate and bile acid, in the photoacoustic spectrum, have been established and compared with the UV–Visible absorption spectrum of acetone solution of powdered gallstone. The results of this investigation show that PAS is better suited to detect the presence of different chemical compounds in gallstones as compared to conventional absorption spectroscopy. Moreover, PAS does not require elaborate biomaterial's sample preparation. Laser induced breakdown spectroscopy (LIBS) has been applied to reveal presence of atomic species in gallstone, that are involved in the molecular constituents revealed by PAS. © 2018PublicationArticle Contaminant concentration in environmental samples using LIBS and CF-LIBS(2010) S. Pandhija; N.K. Rai; A.K. Rai; S.N. ThakurThe present paper deals with the detection and quantification of toxic heavy metals like Cd, Co, Pb, Zn, Cr, etc. in environmental samples by using the technique of laser-induced breakdown spectroscopy (LIBS) and calibration-free LIBS (CF-LIBS). A MATLABTM program has been developed based on the CF-LIBS algorithm given by earlier workers and concentrations of pollutants present in industrial area soil have been determined. LIBS spectra of a number of certified reference soil samples with varying concentrations of toxic elements (Cd, Zn) have been recorded to obtain calibration curves. The concentrations of Cd and Zn in soil samples from the Jajmau area, Kanpur (India) have been determined by using these calibration curves and also by the CF-LIBS approach. Our results clearly demonstrate that the combination of LIBS and CF-LIBS is very useful for the study of pollutants in the environment. Some of the results have also been found to be in good agreement with those of ICP-OES. © 2009 Springer-Verlag.PublicationArticle Effect of dc voltage on the laser optogalvanic spectrum of iodine molecule(1987) A.K. Rai; S.B. Rai; S.N. Thakur; D.K. RaiThe Doppler-limited laser optogalvanic spectrum of the B-X system of I2 molecule has been recorded in the 570-630 nm region. It is found that the discrete spectrum of the B-X system is superposed over a weak continuum extending throughout this region. Upon increasing the applied voltage, the signal corresponding to some of the discrete bands in the lower wavelength region changes sign (from positive to negative). The continuum signal in the region 570-605 nm changes from positive to negative while the other part is much less affected by a change of voltage. © 1987.PublicationArticle Effect of substitution on the electronic spectra of benzaldehyde(1979) M.K. Haque; S.N. ThakurThe effects of substitution of a ring hydrogen atom of benzaldehyde by a fluorine or chlorine atom have been explored by studying the (n, π*) triplet-singlet and singlet-singlet electronic transitions in the three isomeric fluoro- and chlorobenzaldehydes. The changes due to electronic excitation in a number of vibrational frequencies have been used to determine qualitative changes in the molecular geometry of these molecules in going from ground to excited states. © 1979.PublicationArticle Electret microphone for use in photoacoustic spectrometer and photoacoustic spectrum of some rare earth oxide powders(Springer India, 1982) V.N. Rai; L.B. Tiwari; S.N. Thakur; D.K. RaiWe describe a new method for the polarization of an electret foil which has proved very convenient and yields a foil having very good performance in a microphone. The variations in the charge accumulation on the electret foil and its decay with time as well as the variation of the microphone sensitivity with different microphone parameters e.g. different thicknesses of the electret foil, different back plates and different polarization techniques has been investigated. The sensitivity of the home-made microphone is estimated as 1 mV/μbar. The working of this type of microphone and its comparison with a commercial microphone as used in a (laboratory made) single beam photoacoustic spectrometer is discussed. A brief description of the photoacoustic spectrometer including microphone biasing and the photoacoustic cell is given. The photoacoustic spectra of some rare earth oxides in the form of powders have been recorded. It is seen that the atomic levels of triplyionized rare earths which are not fluorescent appear very prominently in the photoacoustic spectrum. The spectra for terbium and praseodymium oxides do not show clear peaks probably due to the presence of different stoichiometric forms. © 1982 Indian Academy of Sciences.PublicationArticle Electronic emission spectra of o- and m-fluorobenzaldehyde vapours(Springer India, 1981) M.K. Haque; S.N. ThakurThe high resolution nπ* electronic emission spectra of o- and m-fluoro-benzaldehyde vapours in the region 365-560 nm excited in a discharge are reported for the first time. The spectra of both the compounds consist of the A 1 A″ -X 1 A′ fluorescence as well as the a 3 A″ -X 1 A′ phosphorescence bands. In the case of o-isomer, all the eleven out-of-plane vibrations have been observed in the fluorescence and the phosphorescence, though weakly in the latter, whereas in the case of m-isomer, only ten have been observed in the fluorescence and nine in the phosphorescence. It is found that the most intense bands in both the fluorescence and the phosphorescence spectra of these molecules belong to the trans-O rotamer. © 1993 Indian Academy of Sciences.PublicationArticle Electronic emission spectrum of p-fluorobenzaldehyde vapour(1978) M.K. Haque; S.N. ThakurThe high resolution electronic emission spectrum of p-fluorobenzaldehyde vapour excited in a discharge is reported for the first time. The spectrum consists of both the ã3A″-X̃1A′ phosphorescence and the Ã1A″-X̃1A′ fluorescence bands. Whereas all the eleven out-of-plane vibrations appear in the fluorescence spectrum, only the φ-CHO torsional vibration and the φ-CHO wagging vibration appear in the phosphorescence. A total of thirty ground state vibrational frequencies out of the thirty-six possible fundamentals have been obtained from the emission bands. Both the fluorescence and the phosphorescence emission spectra of p-fluorobenzaldehyde are very similar to those of benzaldehyde itself. This shows that the electronic transitions are not very sensitive to the substitution of fluorine at the para position of benzaldehyde. © 1978.PublicationArticle Electronic transition moments in the spectra of substituted naphthalenes(Kluwer Academic Publishers-Plenum Publishers, 1981) R.A. Singh; S.N. Thakur[No abstract available]PublicationArticle Excited state normal vibrations and force field of ethynylbenzene(1997) K.M. Singh; R.A. Singh; S.N. ThakurAccurate vibrational frequencies of ethynylbenzene and three of its deuterated isomers in first excited state (1B2) have been used in the determination of intramolecular force constants and the assignments of vibrational frequencies have been discussed in the light of calculated potential energy distributions. The vibrational modes corresponding to normal frequencies ν30 and ν31 exhibit mode scrambling on ring deuteration. Evidence of Duschinsky mixing in going from ground to the excited state has been found in the vibrational modes ν6, ν13, ν31 and ν34 which are active in one photon absorption and also in ν30 which is active in two photon excitation spectrum.PublicationArticle Force constants and mean amplitudes for some anions of MX6 type (X=F, Cl, Br)(1970) D.V.R.A. Rao; S.N. Thakur; D.K. RaiForce constants of the Urey Bradley type for twelve MX6n- ions of Oh symmetry have been reported. Generalized mean square amplitudes and mean amplitudes of vibration for bonded and non-bonded distances have also been calculated. Thermodynamic quantities for these molecules have been calculated at various temperatures from 50° K to 1600° K using a rigid rotator, harmonic oscillator approximation. © 1970 Indian Academy of Sciences.PublicationArticle Force constants of metal hexafluorides(1966) S.N. Thakur; D.K. RaiThe simple and modified UBFF have been applied to thirteen octahedral metal hexafluorides. The force constants have been adjusted by a least squares method. The force constants show certain regularities. The covalent character of the metal fluoride, metal chloride and metal bromide bonds has been discussed. © 1966.PublicationArticle Force constants of molecules with strongly coupled vibrations(1970) S.N. Thakur; S.N. Rai[No abstract available]PublicationArticle Force constants of SF6 from isotopic substitution(1971) S.N. ThakurThe intramolecular force constants governing the F1u vibrational species of the SF6 molecule have been calculated from a knowledge of the isotopic shift of the bending vibration. The effects of anharmonicity on both frequencies of this species are found to be very small and the force constants are nearly as accurate as those obtained from the use of Coriolis coupling constants. A comparison with other force field calculations on this molecule suggests that the ovff model is a good approximation to the true force field. The bond dipole moment and bond moment derivative have also been calculated using the force constants obtained in this work. © 1971.PublicationBook Chapter Fundamentals of Laser Induced Breakdown Spectroscopy(Elsevier, 2007) S.N. Thakur; J.P. Singh[No abstract available]