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21.
Animesh K. Ojha Sunil K. Srivastava B. P. Asthana Ranjan K. Singh 《Journal of Raman spectroscopy : JRS》2007,38(2):159-165
The isotropic and anisotropic parts of the Raman spectra of NH2 bending and ν(CO) stretching modes of HCONH2 in a hydrogen‐bonding solvent, methanol, at different concentrations have been analyzed carefully in order to study the noncoincidence effect (NCE). In neat HCONH2, the experimentally measured values of noncoincidence Δνnc are ∼11 and ∼18 cm−1 for the NH2 bending and ν(CO) stretching modes, which reduce to 0.45 and 1.14 cm−1, respectively at the concentration of HCONH2 in mole fraction, χm = 0.1. The experimental results have been explained on the basis of two models, namely, the microscopic prediction of Logan and the macroscopic model of Mirone and Fini. The relative success of the two models in explaining the experimental data for both the modes have been discussed. It has been observed that in case of the ν(CO) stretching vibrational mode the Logan model can reproduce the experimental data rather precisely, whereas in the case of the NH2 bending mode, Mirone and Fini model yields more accurate results. Copyright © 2006 John Wiley & Sons, Ltd. 相似文献
22.
Animesh K. Ojha Sunil K. Srivastava S. Schlücker W. Kiefer B. P. Asthana Ranjan K. Singh 《Journal of Raman spectroscopy : JRS》2007,38(12):1656-1664
A concentration‐dependent Raman study of the ν(C Br) stretching and trigonal bending modes of 2‐ and 3‐Br‐pyridine (2Br‐p and 3Br‐p) in CH3OH was performed at different mole fractions of the reference molecule, 2Br‐p/3Br‐p, from 0.1 to 0.9 in order to understand the origin of blue/red wavenumber shifts of the vibrational modes due to hydrogen‐bond formation. The appearance of additional Raman bands in these binary systems at ∼617 cm−1in the case of 2Br‐p and at ∼618 cm−1 in the case of 3Br‐p compared to neat bromopyridine derivatives were attributed to specific hydrogen‐bonded complexes formed in the mixtures. The interpretation of experimental results is supported by density functional calculations on optimized geometries and vibrational wavenumbers of 2Br‐p and 3Br‐p and a series of hydrogen‐bonded complexes with methanol. The parameters obtained from these calculations were used for a qualitative explanation of the blue/red shifts. The wavenumber shifts and linewidth changes for the ν(C Br) stretching and trigonal bending modes as a function of concentration reveal that the caging effects leading to motional narrowing and diffusion‐causing line broadening are simultaneously operative, in addition to the blue shift caused due to hydrogen bonding. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
23.
Stimulated Brillouin Scattering has been investigated in a two-electron-temperature plasma and it is found that the growth rate can be controlled by injecting hot electrons in the plasma. For typical values of the magnetosphere plasmas the values of growth rates for different concentrations of hot to cold alectrons are calculated. 相似文献
24.
The LSD (Logic for Structure Determination) program gener-ates organic molecular structures from 1D and 2D NMR data without resorting to chemical shift databases. Its use in the res-olution of natural product structure determination problems has been already reported in the literature. This paper describes how data and structures are internally represented and pro-cessed by LSD to build solution structures. 相似文献
25.
The Nishijima-Mandelstam formula for the transition amplitude of radiative weak decay of baryons is derived within the Bethe-Salpeter formalism in a manner parallel to the Lehmann-Synanzik-Zimmermann reduction procedure. Feynaman rules for bound quarks are discussed. Employing a Gaussian Bethe-Salpeter amplitude for baryons used by other authors, the transition amplitude for + p has been calculated. Due to the use of a phenomenological Bethe-Salpeter wave function, the resulting amplitude turns out to be non-gauge invariant. Gauge invariance is imposed by hand and the asymmetry parameter calculated. Normalization of the decay amplitude and calculation of the absolute rate is not attempted. Two serious problems remain in this calculation: First, the lack of gauge invariance, and, second, the calculated amplitudes turn out to be complex. 相似文献
26.
Using hydrodynamical model of the two-electron-temperatere plasma, the analytical investigation of parametric instability of electron-acoustic wave has been made. It is found that the growth rate decreases with increasing concentration ratio of the hot to the total electrons nh0/n0. The growth rate is found to be more for 相似文献
27.
Ram A. Lal Sanjesh Choudhury Aziz Ahmed Rosmita Borthakur Mrityunjaya Asthana Arvind Kumar 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2010,75(1):212-224
The diamagnetic dioxomolybdenum(VI) complex [(MoO2)2(CH2L)(H2O)2]H2O (1) has been isolated in solid state from reaction of MoO2(acac)2 with bis(2-hydroxy-1-naphthaldehyde)malonoyldihydrazone (CH2LH4) in 3:1 molar ratio in ethanol at higher temperature. The reaction of the complex (1) with electron donor bases gives diamagnetic molybdenum(VI) complexes having composition [Mo2O5(CH2LH2)]·2A·2H2O (where A = pyridine (py, 2), 2-picoline (2-pic, 3), 3-picoline (3-pic, 4), 4-picoline (4-pic, 5)). Further, when the complex (1) is allowed to react with protonic bases such as isonicotinoylhydrazine (inhH3) and salicyloylhydrazine (slhH3), reduction of molybdenum(VI) centre occurs leading to isolation of homobimetallic molybdenum(V) complexes [Mo2(CH2L)(inh)2(H2O)2] (6) and [Mo2(CH2L)(slh)2] (7), respectively. The composition of the complexes has been established by analytical, thermo-analytical and molecular weight data. The structure of the molybdenum(VI) complexes (1)–(5) has been established by electronic, IR, 1H NMR and 13C NMR spectral studies while those of the complexes (6) and (7) by magnetic moment, electronic, IR and EPR spectral studies. The dihydrazone is coordinated to the metal centres in staggered configuration in complex (1) while in anti-cis configuration in complexes (2)–(7). The complexes (6) and (7) possess magnetic moment of 2.95 and 3.06 BM, respectively, indicating presence of two magnetic centre in the complexes per molecule each with one unpaired electron on each metal centre without any metal–metal interaction. The electronic spectra of the complexes are dominated by strong charge transfer bands. All of the complexes involve six coordinated molybdenum centre with octahedral arrangement of donor atoms except in the complex (6), in which the molybdenum centre has rhombic arrangement of ligand donor atoms. The probable mechanism for generation of oxo-group in the complexes (2)–(5) involving coordinated water molecule has been proposed. 相似文献
28.
K. Vikram Nicolae Tarcea S. K. Srivastava B. P. Asthana J. Popp Ranjan K. Singh 《Journal of Raman spectroscopy : JRS》2010,41(9):1067-1075
Raman spectra of 3CHBT in unoriented form were recorded at 14 different temperature measurements in the range 25–55 °C, which covers the crystal → nematic (N) phase transition, and the Raman signatures of the phase transition were identified. The wavenumber shifts and linewidth changes of Raman marker bands with varying temperature were determined. The assignments of important vibrational modes of 3CHBT were also made using the experimentally observed Raman and infrared spectra, calculated wavenumbers, and potential energy distribution. The DFT calculations using the B3LYP method employing 6‐31G functional were performed for geometry optimization and vibrational spectra of monomer and dimer of 3CHBT. The analysis of the vibrational bands, especially the variation of their peak position as a function of temperature in two different spectral regions, 1150–1275 cm−1 and 1950–2300 cm−1, is discussed in detail. Both the linewidth and peak position of the ( C H ) in‐plane bending and ν(NCS) modes, which give Raman signatures of the crystal → N phase transition, are discussed in detail. The molecular dynamics of this transition has also been discussed. We propose the co‐existence of two types of dimers, one in parallel and the other in antiparallel arrangement, while going to the nematic phase. The structure of the nematic phase in bulk has also been proposed in terms of these dimers. The red shift of the ν(NCS) band and blue shift of almost all other ring modes show increased intermolecular interaction between the aromatic rings and decreased intermolecular interaction between two NCS groups in the nematic phase. Copyright © 2009 John Wiley & Sons, Ltd. 相似文献
29.
Studies on azotetrazolate based high nitrogen content high energy materials potential additives for rocket propellants 总被引:5,自引:0,他引:5
R.?Sivabalan M.?B.?TalawarEmail author N.?Senthilkumar B.?Kavitha S.?N.?Asthana 《Journal of Thermal Analysis and Calorimetry》2004,78(3):781-792
This paper reports the synthesis, characterisation and thermolysis studies of a series of azotetrazolate salts, viz., ammonium/guanidinium/triaminoguanidinium [azotetrazolate]. TG-DTA and DSC results of these compounds exhibited their thermal stability up to 180°C. DSC indicated the highest heat release (2804 J g–1) for guanidinium azotetrazolate salt during exothermic decomposition. FTIR of the decomposition products of azotetrazolate salts showed bands at 3264 and 2358 cm–1 which may be attributed to gaseous species such as NH3 and HCN or NH2CN. The sensitivity data suggests low vulnerability of ammonium and guanidinium salts. In cyclic voltammetric studies all the salts showed similar response in reduction reactions. Triamino guanidinium azotetrazolate (TAGAZ) was incorporated into solid propellant formulations in order to establish the compatibility of this class of compounds. DSC results revealed that it does not have adverse effect on thermal stability of double base matrix. The burning rate data obtained indicated that TAGAZ acts as an efficient energetic additive in composite modified double base (CMDB) propellant formulations in high-pressure region.The authors are grateful to Dr. Haridwar Singh, Outstanding Scientist and Director, HEMRL for constant encouragement to carry out this work. Authors also thankful to Dr. R. S. Satpute, Dr. A. N. Nazare and Dr. C. N. Divekar for their assistance in propellant processing. 相似文献
30.
A R Shukla C M Pathak N G Dongre B P Asthana Jacob Shamir 《Journal of Chemical Sciences》1986,97(1):97-115
The infrared spectra of 2,4 dimethylaniline have been recorded in the region 3600-100 cm−1. The Raman spectra with polarization measurements have been recorded and investigated for the first time in the region 3500-100
cm−1. New frequency assignments have been proposed assuming the molecule to possess an approximateC
2 symmetry. Fifty normal modes of the molecule, out of a possible fifty four modes, have actually been observed and assigned
including twenty seven hitherto unreported frequencies. The observed spectral changes give evidence of the presence of an
intermolecular hydrogen bonding of an N−H...N type, and suggest a solid-solid phase transition between 223 and 123 K in the
molecule. 相似文献