Sundara Ramaprabhu

Resonance radiation trapping effects in copper and manganese pure metals and their halides as laser materials have been investigated using Holstein's theory of resonance radiation trapping. Theoretical calculations have been performed for determining the laser-starting and optimum temperatures, and dissociation levels in the metal halides. The results are found to be in excellent agreement with the reported experimental values. A detailed discussion of the results has been presented.

Pure nuclear quadrupole resonance of 127I in H5IO6 has been reported to occur at 44.976 MHz (m = ± 3 2⇌m = ± 1 2 transition) and 83.960 MHz (m = ± 5 2⇌ m = ± 3 2 transition) at 296 K (ref. 1). Using an externally quenched frequency modulated super regenerative spectrometer Zeeman studies have been performed at 296 K on single crystals of H5IO6 growm from aqueous solution by observation of the ± sol3 2⇌± 1 2 transition. The zero-splitting locus method has been employed for the determination of the EFG parameters. The data show that there are two physically inequivalent sites, having average asymmetry parameters, η, of 0.25, located in the unit cell. The maximum field gradient is found to lie along the short bond I-O(2) as suggested by Rama Rao and Weiss (ref. 1). The EFG parameters obtained by detailed molecular orbital calculations (CNDO/2 and INDO method) are compared with the experimental results. © 1983.

The Zeeman effect of the nuclear quadrupole resonance (NQR) lower transition (± 3/2 ↔ 1/2) spectrum for I= 5/2 in crystalline powder has been studied and the frequency splittings of the ±3/2 ↔ ± 1/2 transition line have been plotted as a function of the asymmetry parameter η and the external magnetic field H. The experimental Zeeman frequency splittings of the 127I lower transition line in crystalline powder of H5IO6 have been compared with the theoretical values in order to evaluate η. The present value of n agrees with the earlier values reported from the two transition frequencies and also from a single crystal Zeeman study on the ± 3/2 ↔ ± 1/2 transition line. © 1985, Walter de Gruyter. All rights reserved.

One can not apply the conventional point charge model to evaluate the EFG parameters at the halogen site in chlorates, bromates and iodates since, in XO-3 ions (XCl,Br,I), the halogen atom is covalently bonded to the oxygens of the group and the effect of the cation on EFG is negligible. Therefore molecular orbital calculations by both CNDO/2 and INDO methods have been attempted to evaluate the EFG parameters. The currently available program (ref.1) for CNDO/2 and INDO methods has been extended to III and IV row elements using Hase and Schweig (ref.2) and Deb and Coulson (ref.3) parameters. The EFG parameters obtained from population density matrix (ref.4) from these two methods have been compared with the experimental data wherever available. It has been concluded that CNDO/2 method is better suited for the determination of EFG parameters in XO-3 ions compared to INDO method. The reason for this is discussed. © 1983.

The79Br quadrupole resonance in cadmium, strontium, barium, zinc, magnesium and nickel bromates is studied in the range 77 to 305 K. The temperature dependence of the resonance frequencies in these systems has been analysed on the basis of the torsional motion of the BrO 3 - groups. The torsional frequency and its temperature behaviour have been analysed. © 1984 Indian Academy of Sciences.

Molecular Orbital calculations using the CNDO/2 method have been performed on the BrO2 radicals formed by the γ-irradiation of the single crystals of Zn(BrO3)2 ·6H2O, Cd(BrO3)2 ·2H2O and Sr(BrO3)2 H2O at 300 K in order to evaluate the electric field gradients at the 79Br site. The geometry of the BrO2 radicals in these crystals was obtained from the results of electron spin resonance (ESR) studies at 300 K. The theoretical results are in good agreement with the experimental values deduced from the ESR studies at 300 K on single crystals. © 1985.