Articles written in Proceedings – Section A
Volume 25 Issue 2 February 1947 pp 119-132
The wavelengths of the maxima of all the diffuse bands from 4800 to 2680 A are given. The bands occur in different groups which involve frequency differences of the order of 165 cm.−1, 215 cm.−1 and 360 cm.−1 among the component bands. Five groups of bands with frequency difference of 165 cm.−1 are explained in Paper I. In this paper five groups with frequency differences of 215 cm.−1 and another five groups with frequency differences of 360 cm.−1 among the component bands are discussed. It is shown that they arise in a transition from two initial stable states with frequencies of 215 cm.−1 and 360 cm.−1 to a common set of five different final states which are all unstable. These final states are identified with just those states which are the only theoretically possible ones. The well-known continuum at 3416 A which occurs in emission and in absorption at high temperature is attributed to the transition 1
Volume 25 Issue 2 February 1947 pp 133-137
The three broad bands at 4747·2, 4662·1 and 4575·2 A are explained as due to transitions from a single stable state 1
Volume 25 Issue 2 February 1947 pp 138-150
A large number of new diffuse bands in the emission spectrum of bromine are recorded. The wavelengths of all the diffuse bands of bromine in the region 4200–2000 A are given together with the experimental details. The bands occur in different sets of groups which involve frequency differences of the order of 330, 220 and 480 cm.−1 among the component bands. These are explained, as in the case of iodine, as arising in three initial states 1
Volume 25 Issue 3 March 1947 pp 1- Erratum
Volume 26 Issue 1 July 1947 pp 22-30
Wavelengths of the maxima of continuous bands of chlorine in the ultra-violet obtained with uncondensed transformer discharge, are given. These are practically the same as were previously recorded by other observers. The chlorine spectrum is shown to be apparently similar to that of iodine and bromine. The bands are conveniently arranged in three sets which are shown to be respectively arising in the three states
Volume 44 Issue 2 August 1956 pp 72-82
The overlap factors for bond electrons in various diatomic halides are calculated making use of a simple relation where the overlap factor is an inverse exponential function of the difference between the two atomic radii of the molecule concerned. These overlap factors together with the hybridization values of 15 percent for Cl, and 10 percent for Br and I are used to calculate the ionic characters for various diatomic molecules from the values of the nuclear quadrupole coupling constants obtained by earlier workers. These ionic characters are then plotted against electronegativity differences and the points are found to be fairly well represented by a smooth curve. It is shown that this curve can in general be used for the determination of the ionic characters in the halogen containing single bonds of certain polyatomic molecules. The quadrupole coupling constants are calculated from the ionic characters obtained from the curve and are compared with those observed. The effects of the distortion of the closed shells and of the neighbouring ions on
Volume 46 Issue 4 October 1957 pp 251-264
Bromine was excited by an uncondensed transformer discharge in the presence of argon. The spectrum obtained was found to be different from what one gets without the presence of a foreign gas and consists of (1) a short discrete band system in the region 3150–2970 Å, (2) an extensive discrete band system in the region 2950–2670 Å, (3) a short and weak discrete system in the region 2660–2590 Å and a set of diffuse bands in the region 3340–3190 Å. The wavelengths and wave numbers of the band heads of the system 2950–2670 Å, as obtained from the measurements of the plates taken on the first order 21-ft. grating spectrograph, are given along with the vibrational analysis. This system is shown to be due to a transition from an upper electronic state at 51802 cm.-1 with ω′e = 150·5 cm.-1 and ω′e
Volume 46 Issue 6 December 1957 pp 416-421
The wavelengths and wavenumbers of the band heads of the system 3150–2970 Å as obtained from the plates taken on the first order 21′ grating spectrograph are given along with the vibrational analysis. This system is shown to be due to a transition from an upper electronic state at Te = 48516 cm.-1 with ω′
Volume 47 Issue 3 March 1958 pp 150-160
IBr vapour was excited in the presence of argon by an uncondensed transformer discharge. Four band systems were obtained in the regions 5425–5360 Å, 4520–4415 Å, 4120–4010 Å and 3915–3540 Å of which the first three are discussed in this paper. The wavelengths and wavenumbers of the band heads in three systems as measured from the plates obtained with a 3-prism Steinheil glass spectrograph are given along with their visually estimated relative intensities. The three band systems, which are new, are analysed and the following vibrational constants expressed in cm.−1 are obtained:
The lower state of the first two systems has been identified with the (O+) state at 16814 cm.−1 reported earlier by Brown from a study of the absorption bands in the visible region.
Volume 47 Issue 3 March 1958 pp 161-174
Wavelengths and wavenumbers of the band heads in the region 3915–3540 Å are recorded as obtained from the measurements of the plates taken on a first order 21-feet grating spectrograph. Earlier workers recently reported 40 bands of this system covering the region 3900–3800 Å. All the bands of this system obtained in the present experiments are analysed as involving the3
The probable electronic configurations and electronic terms for the different observed states of IBr are discussed.
Volume 47 Issue 4 April 1958 pp 263-263 Erratum
Volume 49 Issue 2 February 1959 pp 117-127
The spectrum of chlorine excited in the presence of argon has been photographed with a 21-ft. grating spectrograph in the first order. Two band systems in the region 2600–2390 Å and 2365–2239 Å are observed which appear to be respectively analogous to the 2950–2670 Å and 2660–2590 Å systems of bromine reported earlier by Venkateswarlu and Verma. The wavelengths and the wavenumbers of all the bands in the system 2600–2390 Å are given. The vibrational scheme along with the corresponding Franck-Condon parabola is also given. The analysis suggests that the lower state of the system is the 3π(O
Volume 50 Issue 4 October 1959 pp 254-258
The nuclear magnetic resonance shifts (chemical shifts) of Cl35 in aqueous solutions of alkali chlorides were determined using a High Resolution NMR Spectrometer. These small shifts probably represent the effect of the neighbouring atom even in the highly ionic state. A similarity of these results to the quadrupole coupling constants of the halogen atom in these molecules is pointed out.
Volume 51 Issue 1 January 1960 pp 14-27
Bismuth chloride has been excited in flowing condition with an uncondensed transformer discharge. About 390 bands are observed in the present experiments of which only 140 were recorded by earlier workers. The vibrational constants obtained are the same as those obtained by Morgan from obsorption experiments except for the addition of a cubic term for the upper state. It appears quite likely that the upper state of the system dissociates into Bi (4S3/2) + Cl (2P1/2) while the lower state, which is probably the ground state, dissociates into Bi (4S3/2) + Cl (2P3/2). The rough values of the dissociation energies obtained by extrapolations are D0′=3750 cm.−1 and D0″=24614 cm.−1
Volume 52 Issue 3 September 1960 pp 109-121
High resolution H1 and F19 nuclear magnetic resonance spectra of 1-fluoro, 2, 4-dinitrobenzene were obtained and analyzed to determine all the parameters involved. As the spectrum of one of the protons is well separated from that of the other two, the secular equation has been solved in the first approximation. The analysis gives the following spin-spin coupling constants: J0HH = 8.7 ± 0.3 cps., JmHH = 2.9 ± 0.2 cps., JpHH = 0.6 ± 0.3 cps., J0HH = 10.4 ± 0.2 cps., and the two meta H-F coupling constants were found to be considerably different being 6.5 ± 0.3 cps. and 3.8 ± 0.3 cps. It has been found that the
Volume 54 Issue 6 December 1961 pp 305-320
The ring proton resonance spectra of
Volume 62 Issue 5 November 1965 pp 249-251
Divalent ions when doped in alkali halide single crystals will go in alkali sites and form associate pairs with neighbouring cation vacancies or other impurity defects. As there will be sets of equivalent positions for such associated pairs, their energy levels will be degenerate. The reducible representations of these associated pairs involving first to sixth nearest neighbours have been reduced to the corresponding irreducible representations of the point group O
Volume 63 Issue 5 May 1966 pp 284-292
The electron spin resonance spectra of Mn2+ in NaCl single crystals are investigated in detail. Seven different spectra (I, II, III1, III2, IV, V and VI) are observed. The spectra I–IV are the same as those observed by earlier workers, while the spectra V and VI are observed here for the first time. The local symmetry at the paramagnetic ion is orthorhombic for the spectra IV and V and tetragonal for the spectrum VI about the crystallographic  direction. The properties of the spectrum IV are explained in terms of an associated pair Mn2+: O22− with O22− molecular ion at the nearest neighbour anion site in the  direction with its internuclear axis in the (001) plane. The spectrum V is assigned to the associated pair Mn2+: O22− coupled with a nearby cation vacancy in the  direction and the spectrum VI to Mn2+ ion associated with OH− ion at the anion site in the  direction with a probable second neighbour cation vacancy. All the observed spectra are analysed in terms of the parameters of the usual spin-Hamiltonian.
Volume 63 Issue 5 May 1966 pp 311-315
Forbidden hyperfine transitions are observed in the electron spin resonance spectrum of divalent Mn55 ion in NaCl single crystal for a particular associated pair. From the measurements of the M = + 1/2 → −1/2, Δm = ± 1 transitions the parameters
Volume 64 Issue 1 July 1966 pp 9-12
Iodine when excited in the presence of argon shows three band systems in the regions 4420–4000 Å., 3,460–3015 Å. and 2785–2731 Å. all of which involve O
Volume 64 Issue 5 November 1966 pp 275-282
The electron paramagnetic resonance of Mn2+ in KNO3 single crystal is investigated over a temperature cycle through transition temperatures. The hyperfine coupling constant, A, half width,
Volume 64 Issue 6 December 1966 pp 321-326
Exchange of intensities among various spectra of Mn2+ in NaCl single crystal, corresponding to Mn+2 ion associated with various point defects, is described as a function of temperature and time. The variation of line width with temperature is discussed. The fine structure parameter D for a particular spectrum is measured with temperature and is shown to behave like D=D0 (1+
Volume 65 Issue 4 April 1967 pp 211-218
The Paramagnetic Resonance of Gd3+ in SmCl3·6H2O single crystals, grown from solution, is studied at room temperature. A six line spectrum for H//Z and a seven line spectrum for H//X corresponding to ΔM=± 1 transitions are observed. Their angular variation in ZX plane from
Volume 65 Issue 6 June 1967 pp 361-367
The paramagnetic resonance spectrum of Gd3+ in Pr(NO3)3·6H2O single crystals, is studied at room temperature. A seven line spectrum for H//Z as well as for H//X corresponding to ΔM=±1 transitions is observed along with a number of low field transitions (ΔM⩾2). The spin-Hamiltonian analyses is presented.
Volume 66 Issue 4 October 1967 pp 208-221
Electron Paramagnetic Resonance studies of Cu2+ doped in NH4Br single crystals have been carried out for the first time. The room temperature data reveal that Cu2+ ions go predominantly to interstitial sites having square planar co-ordination of four Br− ions. For this type of complexes the bromine: superhyperfine structure: is observed on the normal hyperfine structure lines of copper. Existence of other weak spectra indicates that a relatively few Cu++ ions go substitutionally to (NH4)+ ions, and are probably associated with a first or a second nearest neighbour cation vacancy, among the two, the latter being more predominant. However, the low temperature studies corresponding to the tetragonal phase of NH4Br indicate that a number of Cu2+ ions at interstitial sites get readjusted to the lattice sites after phase transformation. The spectra in both the phases are analysed by the usual spin Hamiltonian method.
Volume 67 Issue 3 March 1968 pp 130-137
Electron paramagnetic resonance investigation of Mn2+ in (NH4)2SO4 single crystal is discussed both in paraelectric and ferroelectric phases of the crystal. Mn2+ is found to substitute one of the two possible types (
Volume 69 Issue 2 February 1969 pp 67-77
The electron paramagnetic resonance of Mn2+ in NaF single crystals is investigated at different temperatures from 573° K to 93° K. Four different spectra designated as I, II, III2 and III4 are observed. Spectrum I consists of a single broad resonance corresponding to precipitated Mn2+ ions. Spectrum II is isotropic and centred near
Volume 69 Issue 6 June 1969 pp 307-315
Electron paramagnetic resonance (EPR) of VO2+ radicals incorporated in face-centred single crystals of NaCl, KC1 and RbCl has been studied in the temperature range of 77° K to 330° K. At liquid nitrogen temperature, anisotropic spectra have been recorded in each case while spectra recorded at room and higher temperatures are isotropic suggesting the existence of a fast readjustment of VO2+ molecular ions in the crystals at higher temperature while this motion gets hindered at liquid nitrogen temperatures. Spin-Hamiltonian constants are calculated from the recorded isotropic and anisotropic spectra. The line widths in each case are found to obey a parabolic law originally proposed by Kivelson. The constants which give a close fit have been evaluated. The random orientation and readjustment of V-0 bond in these alkali chloride crystals is explained on the assumption that the medium exhibits a “liquid-like” nature for VO2+ molecular ion as far as the electron paramagnetic resonance absorption is concerned.
Volume 71 Issue 2 February 1970 pp 49-55
Electron paramagnetic resonance spectrum of the Cu2+ ion in CsCl is studied at different temperatures. The local symmetry at the Cu2+ site is found to be tetragonal. A model of substitutional Cu2+ ion associated with a first neighbour cation vacancy is proposed to explain the observed spectrum.
Volume 72 Issue 6 December 1970 pp 249-260
The absorption spectrum of Co2+ doped NH4Cl has been studied from the room temperature to the liquid nitrogen temperature. A sudden change in the spectrum is observed between 243° K and 233° K which is attributed to the phase transition in the crystal. From the observed spectrum it is suggested that Co2+ goes in interstitially as well as substitutionally. Both the types of centers exist at room temperature, but with decrease in temperature substitutional ions migrate to interstitial sites, the process being stimulated at the phase transformation point so that the 77° K spectrum seems to be mostly due to the interstitial centers. The 77° K spectrum is analyzed in the approximation of octahedral symmetry for interstitial ions and the band positions are fitted fairly well with B = 870 cm.−1 Dq = 850 cm.−1 and C = 4·4 B. A blue shift of about 100 cm.−1 is observed for4T1 (P) band at the phase transition which is attributed to the increase in Dq value with the anomalous lattice contraction at the phase transition. The decrease in the lattice parameter calculated from this blue shift is around 0·4% which is in good agreement with the results of X-ray measurements. Two possible models for the interstitial complex are examined and the one with fourfold chlorine coordination associated with two neutral water molecules at the first neighbour (NH4)+ site lying along < 100> direction is suggested to be more probable.
Volume 74 Issue 1 July 1971 pp 34-52
Electron paramagnetic resonance (EPR) of divalent manganese ion has been studied at 9.5 KMc/sec. These studies reveal that Mn2+ ion substitutes at a β-Cs+ site and gets associated with a vacancy at a neighbouring β-Cs+ site in the aft-plane. The
Volume 74 Issue 5 November 1971 pp 230-242
Raman spectrum of a Cs2SO2 single crystal has been recorded and measured using an Ar+ laser as a source of excitation. The polarization behaviour of the Raman lines under different crystal orientations has been studied. Symmetry co-ordinates of the Raman active lattice modes as worked out from group theoretical concepts are presented.