R.J. Kshirsagar

Intensities of lines in the bands ν2 and ν4 and the transition dipole moments of PH3

Abstract The absolute intensities of 57 vibration-rotational spectral lines of transitions to the vibrational states v 2 = 1 and v 4 = 1 of PH 3 have been measured with a diode laser. With account being taken of the mixing of the wavefunctions of both vibrational states, the values of the vibrational transition moments and their relative signs were determined by a least-squares fit to the experimental data: 〈0, 0 0 ∥ μ z ∥1, 0 0 〉 = (0.23913 ± 0.00093) × 10 −30 C m and 〈0, 0 0 ∥ μ x ∥0, 1 ±1 〉 = −(0.14060 ± 0.00137) × 10 −30 C m.

Density functional study of α-amino acids: structural, energetic and vibrational properties

The structural, energetic and vibrational properties of the 20 standard α-amino acids, in each of several different low-energy conformations, have been investigated using all-electron density-functional theory. The Becke–Perdew exchange-correlation potential within the generalized gradient corrections to the local density approximation exchange and correlation energy was used, along with a Slater-type expansion of the Kohn–Sham orbitals. The structures and bond lengths, conformation energies, and infrared vibrational spectra of the stable conformers of these molecules have been predicted and various features, including those arising due to intramolecular hydrogen bonding, identified. The results of our accurate ab initio study, the most comprehensive to date, are in good agreement with the few earlier gas-phase experimental and theoretical results available from the literature, and provide a benchmark for further experiments and for obtaining a deeper understanding of this vital class of biomolecules.

Fourier-transform spectroscopic study of the rotational intensity distribution in the first positive B3Πg–A3Σu+ band system of the nitrogen molecule

Abstract In the present work we have studied the rotational intensity distribution in the 0–0, 0–1 and 1–3 bands of the B3Πg–A3Σu+ system of N2 recorded on a Fourier transform spectrometer. The effective Hamiltonian used by Roux et al. (J. Mol. Spectrosc. 97 (1983) 253) for reduction of the experimental line position data to molecular parameters, is found to be adequate in reproducing the observed line intensities. To enhance the accuracy of the theoretical line intensity calculations, it proved necessary to use rotation-dependent Frank–Condon factor. Using the calculated intensities, it was possible to identify certain rotational lines belonging to the weakest branches Q13 and Q31, not reported before.

Thermally Grown Oxide Layer on Aluminized Superalloy 690 Substrate and its Stability in Nitrate-Based Environment

Aluminides were formed on Ni-Cr-Fe based superalloy 690 substrates using pack aluminization process at 1273 K in controlled atmosphere. Thermal oxidation of aluminized specimens was carried out at 1273 K for a total period of 4 hours in air. The thermally grown oxide layer was examined using X-ray diffraction (XRD) studies on top surface and scanning electron microscopy (SEM) with energy dispersive spectroscopy (EDS) analysis along the cross-section of the sample. The oxide layer developed on aluminized superalloy 690 substrate consisted of Al2O3 layer with a thickness of about 2 μm. The oxidized specimens were exposed in nitrate-based environment (simulated high-level nuclear liquid waste) at 373 K for a total period of 216 hours. A good adherence of aluminide coatings was noticed even after prolonged exposure in nitrate-based solution with a little amount of material dissolution from the edges of the specimens. XRD studies on exposed specimen indicated existence of Al2O3 layer on the top surface, which is believed to have resulted in good adherence of aluminide coatings.

How universal are hydrogen bond correlations? A density functional study of intramolecular hydrogen bonding in low-energy conformers of α-amino acids

Hydrogen bonding is one of the most important and ubiquitous interactions present in Nature. Several studies have attempted to characterise and understand the nature of this very basic interaction. These include both experimental and theoretical investigations of different types of chemical compounds, as well as systems subjected to high pressure. The O–H..O bond is of course the best studied hydrogen bond, and most studies have concentrated on intermolecular hydrogen bonding in solids and liquids. In this paper, we analyse and characterise normal hydrogen bonding of the general type, D–H...A, in intramolecular hydrogen bonding interactions. Using a first-principles density functional theory approach, we investigate low energy conformers of the twenty α-amino acids. Within these conformers, several different types of intramolecular hydrogen bonds are identified. The hydrogen bond within a given conformer occurs between two molecular groups, either both within the backbone itself, or one in the backbone and one in the side chain. In a few conformers, more than one (type of) hydrogen bond is seen to occur. Interestingly, the strength of the hydrogen bonds in the amino acids spans quite a large range, from weak to strong. The signature of hydrogen bonding in these molecules, as reflected in their theoretical vibrational spectra, is analysed. With the new first-principles data from 51 hydrogen bonds, various parameters relating to the hydrogen bond, such as hydrogen bond length, hydrogen bond angle, bond length and vibrational frequencies are studied. Interestingly, the correlation between these parameters in these bonds is found to be in consonance with those obtained in earlier experimental studies of normal hydrogen bonds on vastly different systems. Our study provides some of the most detailed first-principles support, and the first involving vibrational frequencies, for the universality of hydrogen bond correlations in materials.