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Showing papers by "Indian Association for the Cultivation of Science published in 1980"



Journal ArticleDOI
TL;DR: In this article, a time-resolved study of the emission from benzil and naphthyl in semi-solid glasses (e.g., alcoholic glass near the melting point) using a pulsed N2-laser as an excitation source is reported.

44 citations


Journal ArticleDOI
TL;DR: In this article, the effect of heat treatment in air on dark and photoconductivity of CdS films has been studied, and the results for Hall mobility and carrier concentration have been found to be primarily due to high carrier concentration.
Abstract: Thin films of highly purified CdS have been prepared by the vacuum evaporation method. The source has been maintained at 850°C and a semi-closed system has been used for evaporation. The following properties of the films have been studied, viz: (1) dark and photoconductivity as functions of temperature and thickness of the films (2) Hall mobility and carrier concentration at room temperature (3) optical absorption and spectral response and (4) structural studies by X-ray diffraction. The resistivity of the films varies from 0.15 to 3.7 Ωcm as the thickness of the films decreases from 13600 to 1200 A. The transmittance of the films has been found to be 80-90%. The results for Hall mobility and carrier concentration show that the comparatively low resistivity of CdS films obtained by us is primarily due to high carrier concentration. The photoconductive gain increases with a decrease in film thickness. The effect of heat treatment in air on dark and photoconductivity has been studied.

41 citations


Journal ArticleDOI
TL;DR: In this article, the magnetic susceptibility in the three principal crystallographic directions, and the electrical conductivity and thermoelectric power parallel and perpendicular to the basal plane of Sb 2 Se 3 single crystals, have been measured over the temperature range 100-550 K. The different results obtained from the magnetic and electric studies have been accounted for on the basis of non-stoichiometry of the compound and localized lone electrons.

38 citations


Journal ArticleDOI
TL;DR: In this article, the superexchange mechanism has been investigated and it is shown that the O bridge can bring about considerable antiferromagnetic interaction and the lower limit of the exchange integral ∣J∣ is set at ∼350 cm−1.

35 citations


Journal ArticleDOI
TL;DR: In this article, the authors apply linear response function theory in a coupled-cluster framework and show that linear response functions can be applied to a variety of problems in a wide range of applications.
Abstract: (1980). Application of linear response function theory in a coupled-cluster framework. Molecular Physics: Vol. 39, No. 2, pp. 519-524.

26 citations


Journal ArticleDOI
Abstract: In this paper we evaluate some higher-order terms in the eikonal expansion of the $T$ matrix for potential scattering. We calculate eikonal correction terms which are of second order in potential strength ${V}_{0}$ through seventh order in inverse momentum ${K}^{\ensuremath{-}1}$, which leads us to conjecture two plausible formulas for general eikonal correction terms of $O({K}^{\ensuremath{-}2n}{{V}_{0}}^{2})$ and of $O({K}^{\ensuremath{-}2n\ensuremath{-}1}{{V}_{0}}^{2})$. This may enable us to obtain an eikonal expansion of the second Born amplitude for any type of potential. We further evaluate eikonal correction terms which are of third order in potential strength and fourth and fifth order in ${K}^{\ensuremath{-}}$. With the help of eikonal corrections evaluated in this paper, a general formula based on a WKB phase function, and a relation existing between the amplitude term and the eikonal phase of the impact-parameter representation of the scattering $T$ matrix, we are able to determine the $T$ matrix completely through fourth order in inverse momentum. We may also note that the formula for the eikonal correction term of $O({K}^{\ensuremath{-}2n\ensuremath{-}1}{{V}_{0}}^{2})$ when generalized in a suitable manner surprisingly yields the expression for the explicitly evaluated eikonal correction term of $O({K}^{\ensuremath{-}5}{{V}_{0}}^{3})$. It is further shown in this paper that the previously mentioned conjectured formula for the general eikonal phase correction term of $O({K}^{\ensuremath{-}2n\ensuremath{-}1}{{V}_{0}}^{2})$ is somewhat supported by the form of the corresponding correction term to the usual WKB phase-shift result. All the higher-order eikonal correction terms evaluated in this paper vanish for the Coulomb interaction.

25 citations


Journal ArticleDOI
TL;DR: In this article, the anomeric configurations of different sugar residues in the whole-gum polysaccharide were determined by chromium trioxide oxidation of the acetylated polysacchide.

21 citations


Journal ArticleDOI
TL;DR: In this paper, the validity of the compensation rule is studied for some polyene semiconductors namely, β-apo-8′-carotenal, astacene, and methyl bixin.
Abstract: The validity of the compensation rule is studied for some polyene semiconductors namely, β-apo-8′-carotenal, astacene, and methyl bixin. The value of the activation energy (E) of these semiconductors is varied by adsorbing different vapours and also different amounts of a particular vapour. The adsorbed vapours increase the semiconduction currents of these polyenes by several orders of magnitude with a simultaneous increase in the semiconduction activation energies (E). Such change depends on the chemical nature and also on the amount of a vapour adsorbed. It is observed that these polyene semiconductors follow a three-parameter equation σ(T) = σ0' exp (E/2kT0) exp (–E/2kT) where σ0' and T0, the characteristic or compensation temperature, are constants for a substance. Various methods used for evaluating the semiconduction parameters T0 and σ'0 yield consistent results suggesting a physical basis for the compensation effect. The compensation temperature is found to play an important role in the dark conduction process in these polyene semiconductors. Die Gultigkeit der Kompensationsregel wird fur einige Polyen-Halbleiter wie β-Apo-8′-carotenal, Astazen und Methylbixin untersucht. Der Wert der Aktivierungsenergie (E) dieser Halbleiter wird durch Adsorption verschiedener Dampfe sowie unterschiedlicher Mengen eines speziellen Dampfes geandert. Die adsorbierten Dampfe erhohen den Halbleiterstrom in diesen Polyenen um einige Grosenordnungen bei gleichzeitigem Anwachsen der Aktivierungsenergie (E) der Halbleitung. Diese Anderung hangt von der chemischen Natur und auch von der Menge des adsorbierten Dampfes ab. Es wird beobachtet, das diese Polyen-Halbleiter eine dreiparametrige Gleichung σ(T) = σ'0 exp (E/2kT) befolgen, wo σ'0 und T0, die charakteristische oder Kompensationstemperatur, Konstanten fur eine Substanz sind. Verschiedene Methoden, die zur Berechnung der Halbleiterparameter T0 und σ'0 benutzt werden, ergeben konsistente Ergebnisse, die auf eine physikalische Grundlage fur den Kompensationseffekt hinweisen. Es wird gefunden, das die Kompensationstemperatur eine wesentliche Rolle bei der Dunkelleitung in diesen Polyen-Halbleitern spielt.

17 citations


Journal ArticleDOI
TL;DR: In this article, the detection of fluorescence from unrelaxed S 1 state of benzil using boxcar gating technique is reported, which exhibits mirror image relationship with absorption and blue shift in hydroxylic solvent.

17 citations


Journal ArticleDOI
TL;DR: Five oligosaccharides were isolated in pure state from the lipopolysaccharide of Vibrio cholera, Inaba 569 B, and the their structures were elucidated.

Journal ArticleDOI
TL;DR: In this article, statistical Green's function theory has been successfully applied to study the ferroelectric phase transitions in the Rochelle Salt and its deuterated form with two sub-lattice pseudo-spin model containing spin-phonon interaction terms.
Abstract: Statistical Green's function theory has been successfully applied to study the ferroelectric phase transitions in the Rochelle Salt and its deuterated form with two sub-lattice pseudo-spin model containing spin-phonon interaction terms. The Blinc-de Gennes model parameters have been calculated for both of the salts. A phenomenological explanation of the isotope and the impurity dependence of the transition temperatures has also been sought from our calculations. The origin of non-logarithmic behaviour of the heat capacity has been attributed to the strong proton-phonon and anharmonic interactions. Finally, renormalized phonon frequency and the temperature dependence of the soft mode frequency have been studied theoretically. The present study suggests that phase transitions for the Rochelle Salt and its deuterated variety can be understood by a displacive mechanism.

Journal ArticleDOI
TL;DR: In this paper, the Hall effect in copper-nickel films was measured at temperatures in the range 30-150 °C as a function of the magnetic field and the ordinary and extraordinary terms of the Hall coefficient were determined from the observed experimental data.

Journal ArticleDOI
TL;DR: In this article, the polarized absorption spectra of Ni2+ doped in Cs2CdCl4 single crystals at 295 and 77 K in the range 5000 to 25000 cm−1.
Abstract: The polarized absorption spectra are reported of Ni2+ doped in Cs2CdCl4 single crystals at 295 and 77 K in the range 5000 to 25000 cm−1. Emission and excitation spectra are also reported in the range 11000 to 25000 cm−l. The Ni2+ ions occupy the Cd2+ sites in octahedral geometry and the spectra are satisfactorily interpreted in terms of a cubic ligand field model including spin-orbit coupling. The ligand field parameters evaluated to best fit the observed spectra are Dq = 600 cm−1, F2 = 1260 cm−1, F4 = 87 cm−l, und λ = 290 cm−l. No strong spectral evidence for tetragonal distortion is observed. Die Polarisations-Absorptions-Spektren von Ni2+ -dotierten Cs2CdCl2-Einkristallen werden bei 295 und 77 K im Bereich von 5000 bis 25000 cm−l sowie die Emissions- und Anregungsspektren im Bereich 11 000 bis 25000 cm−l untersucht. Die Ni2+-Ionen besetzen Cd2+-Platze in oktaedrischer Anordnung, und die Spektren werden befriedigend mit einem kubischen Ligandenfeldmodell unter Einschlus von Spin-Bahn-Kopplung interpretiert. Die Ligandenfeldparameter, die die beobachteten Spektren am besten anpassen, sind Dq = 600 cm−1, F2 = 1260 cm−1, F4 = 87 cm−1 und λ = 290 cm−1. Fur eine tetragonale Verzerrung wird aus den Spektren kein deutlicher Hinweis beobachtet.

Journal ArticleDOI
TL;DR: In this paper, the mixing of states induced by a high magnetic field was exploited to intensify and locate a forbidden A1 → A1 transition in Na3Pr(C4H4O5)3·2NaClO4·6H2O single crystal.

Journal ArticleDOI
TL;DR: In this article, an average holepotential method (AHP) for studying molecular electronic structures and properties in excited states is suggested, and the improved virtual orbitals (IVOs) are adapted to all possible transitions on the average.

Journal ArticleDOI
TL;DR: In this paper, the relaxations due to vacancies in copper have been calculated using lattice statics method using phonon dispersion relation of copper by Sinha and the elastic constants as constraints, the dynamical matrix is derived including interactions up to five neighbours.
Abstract: The relaxations due to vacancies in copper have been calculated using lattice statics method. Using the measured phonon dispersion relation of copper by Sinha and the elastic constants as constraints, the dynamical matrix is derived including interactions up to five neighbours. Unlike most of the previous calculations all the neighbours are found to relax towards the vacancy. Distortions are found to be large in close-packed directions as compared to the directions along the cube axes in the crystal. Die Relaxationen infolge von Leerstellen werden mit der statistischen Gittermethode berechnet. Mit der gemessenen Phononendispersionsbeziehung nach Sinha und den elastischen Konstanten wird die dynamische Matrix abgeleitet, die Wechselwirkungen bis zu funf Nachbarn einschliest. Im Gegensatz zu den meisten fruheren Berechnungen wird gefunden, das alle Nachbarn in Richtung der Leerstelle relaxieren. Es wird weiter gefunden, das die Verzerrungen in den dichtgepackten Richtungen gros sind, verglichen zu den Richtungen entlang der kubischen Achsen im Kristall.


Journal ArticleDOI
TL;DR: In this article, the complex energy-band structures of AgCd alloys have been determined by the alloy-Koringa-Kohn-Rostoker-Ziman (KKRZ) method for two different concentrations, and the optical properties estimated from these calculations have been compared with experiment.
Abstract: Complex energy-band structures of AgCd alloys have been determined by the alloy--Koringa-Kohn-Rostoker-Ziman (KKRZ) method for two different concentrations, and the optical properties estimated from these calculations have been compared with experiment. On the low-concentration side agreement with experiment is found to be excellent, whereas on the higher-concentration end a slight deviation is observed. This is probably due to the fact that the average-T-matrix approximation, which is the basis of the alloy--KKRZ method, is more suited for relatively lower concentrations of the alloying material. An effect of the charge transfer on the higher-concentration alloys has also been investigated. The results show that the disagreement with the experiment can also be accounted for by the charge-transfer effect.


Journal ArticleDOI
TL;DR: In this article, the method of calculating CNDO bonding parameters for transition metal atoms was extended to transition metal ions, and the results were compared with those obtained by conventional cNDO-MO calculation.
Abstract: The method of calculating CNDO bonding parameters developed recently is extended to transition metal atoms. It is shown that one of the approximations introduced earlier can also be deduced by a more complete treatment of the imbalance problem in CNDO-MO theory. The conventionally calibrated bonding parameters indirectly incorporate important contributions from two-particle interactions. The parameters developed are used to compute the coefficients of metal-to-ligand transfer of spin in many hexafluro metallate ions of transition metals. The results are compared with those obtained by conventional CNDO-MO calculation. Comparison of the computed bonding parameters with other available values is also made.

Journal ArticleDOI
TL;DR: In this paper, the static dipole quadrupole polarizabilities and shielding factors were calculated using the variation perturbation technique in a coupled Hartree-Fock scheme, and the results compare favorably with the existing values.
Abstract: The static dipole quadrupole polarizabilities and shielding factors of Mg, ${\mathrm{Al}}^{+}$, ${\mathrm{Si}}^{2+}$, ${\mathrm{P}}^{3+}$, ${\mathrm{S}}^{4+}$, ${\mathrm{Cl}}^{5+}$, and ${\mathrm{Ar}}^{6+}$ have been calculated using the variation perturbation technique in a coupled Hartree-Fock scheme. For the dipolar calculation the two innermost cores have been kept frozen, whereas for the quadrupolar calculation all the cores have been relaxed. The results compare favorably with the existing values. For the quadrupolar shielding factor in all cases an antishielding effect is noted. Systematic behavior is observed for the isoelectronic polarizability values.

Journal ArticleDOI
TL;DR: In this article, a nonperturbative iterative variational method has been applied to the bound polaron problem, where the electron-phonon Hamiltonian is reduced in successive orders resulting in a transformed electronic Hamiltonian which gets an attractive phonon-induced potential from each order of reduction.
Abstract: For pt.I see Phys. Lett. A, vol.71, p.385 (1979). A recently developed non-perturbative iterative variational method has been applied to the bound polaron problem. The electron-phonon Hamiltonian is reduced in successive orders resulting in a transformed electronic Hamiltonian which gets an attractive phonon-induced potential from each order of reduction. The transformed electronic Hamiltonian has been solved numerically for a series of values of the parameters alpha , beta . Relation to perturbative solutions is discussed. Interesting localisation criteria derived from the calculated wavefunctions are also discussed.

Journal ArticleDOI
TL;DR: In this article, it is shown that the arguments leading to such a conclusion are not entirely justified and that the inapplicability of the sign-change argument in perturbation theory is critically analysed.


Journal ArticleDOI
TL;DR: A stereoselective synthesis of the title compound (5) by a route which allows flexibility for an approach to trans -clerodane diterpenes and congeners, is described in this article.

Journal ArticleDOI
01 Aug 1980-Talanta
TL;DR: A simple method for the amperometric estimation of N-cyclohexyl-2-benzothiazole sulphenamide, N-dicyclo hexyl-1,2, and 2-(morpholinothio)benzothsiazole and N-tert.

Journal ArticleDOI
01 Dec 1980-Pramana
TL;DR: In this paper, an alternative definition of the superoperator resolvent for calculation of difference energy satisfying linked cluster theorem for a coupled-cluster choice of the ground-state function which may even be approximate.
Abstract: In this paper it is shown that (i) there exists an alternative definition of the superoperator resolvent for calculation of difference energy satisfying linked cluster theorem for a coupled-cluster choice of the ground-state function which may even be approximate; (ii) the pole-structure of this propagator-like function in superoperator form is shown to contain information similar to that contained in the conventional propagator. (iii) It is demonstrated that suitable “Killer conditions” and completeness of the “operator manifold”—essential for understanding the pole-structure of the propagator—can be established both for an exact and an approximate ground state function in a coupled-cluster form. (iv) It is also demonstrated that difference energies calculated with these propagator-like functions are identical to those obtained from a linear response theory in a coupled-cluster form put forward recently by Mukherjeeet al and Monkhorst.

Journal ArticleDOI
TL;DR: Using statistical Green's function technique exact expression for the transverse electrical susceptibility (x a ) for KDP type crsytals has been derived with the total pseudo-spin lattice coupled mode Hamiltonian as discussed by the authors.

Journal ArticleDOI
TL;DR: In this article, the electrochemical reduction characteristics of molybdenum(VI)-and molybenum(V)-ethylenediaminetetraacetate complexes, [(MoO3)2Y]4− and [Mo2O4Y]2− respectively have been investigated as a function of pH and free ligand concentration.
Abstract: The electrochemical reduction characteristics of the molyb-denum(VI)-and molybdenum(V)-ethylenediaminetetraacetate complexes, [(MoO3)2Y]4− and [Mo2O4Y]2− respectively have been investigated as a function of pH and free ligand concentration. The nature of chemical reduction of these two complexes with sodium borohydride and sodium dithionite have also been studied in acetate and borate buffers. The electroactive species undergoing electrode reductions have been ascertained by analysing polarograms of the complexes. A mechanism has been proposed to account for the differences observed in the reactivities of these two complexes.