Two-photon excitation spectrum of benzonitrile vapour

The two-photon excitation spectrum of benzonitrile in the gas phase at about 1 torr has been recorded and analysed in the total energy region of 36300 to 40500 cm⁻¹ using both linearly and circularly polarised light from a Nd-YAG pumped dye laser. The two-photon spectrum consists of strong Franck Condon (fc) transitions bearing a good resemblance to the one-photon spectrum and also vibronic coupling (vc) transitions essentially arising out of the analogue of the benzeneν ₁₄. By a comparative study of thetp spectra of various other monosubstituted benzenes, it has been inferred that the strongtp spectrum of benzonitrile should be ascribed to a considerableπ charge delocalization over the phenyl and nitrile groups.     

Axiomatic restrictions on scattering amplitudes of hadrons

Problems of expsrimental verification of the quantum field theoretical principles by experimental test of any one of physical corollaries of the axiomatic quantum field theory are shortly discussed. A selective review of available axiomatic restrictions on scattering amplitudes of hadrons is given.The author is very indebted to E. P.Sabad, I. Yu.Krivsky, V. I.Kelemen, and Yu. A.Xaveri for the help offered to him during the preparation of this review. The author is especially indebted to Academician N. N.Bogolyubov for his approval of Theorem XXVIII before publishing it in Ref. [67], as well as to Prof. M. I.Podgoretsky (Dubna) and Prof. V. Ya.Fajnberg (Moscow) for numerous discussions of this theorem and Prof. Yu. M.Shirokov (Moscow) for a preciseful stimulating remark.     

Superconductivity in ordering systems

We analyse the behaviour of 2-order parameter systems (where one subsystem is superconducting) in constant external ordering fields and find the spatial distribution of the order parameters.The authors would like to thank Prof. B. T.Matthias and Prof. T. L.Birman for useful discussions.     

Fluctuations and the magnetic equation of state

The influence of inhomogeneity of magnetization on the equation of state for a magnetic system has been considered in the approximation of homogeneous fluctuations of magnetic moment. The fluctuations have been described in the molecular field approximation. It has been shown that taking into account the fluctuations of magnetic moment at the derivation of the equation of state changes the relation among the variablesM, H andT, the temperature dependence of the spontaneous magnetization near the critical point, and shifts the critical temperature.The author would like to thank Prof. J.Kocinski and Prof. L.Wojtczak for their interest in the subject of the paper and for numerous elucidating discussions. The author is indebted to Prof. L.Valenta for his helpful remarks concerning this paper.     

Spectroscopic studies of Ni2+ in calcium tartrate tetrahydrate

The optical absorption spectrum of a single crystal of calcium tartrate tetrahydrate, doped with Ni²⁺ ions, is investigated at laboratory and liquid nitrogen temperatures. From the analysis of the unpolarised and polarised spectra, the site symmetry of the Ni²⁺ ion is attributed to an elongated octahedron with a small tetragonal (C_4v) distortion.The analysis results in the following crystal field parametersB=875 cm^–1,C=3980 cm^–1,Dq=900 cm^–1, Dt=32cm^–1.The authors wish to express their thanks to the Head of the Department of Physics, I.I.T., Madras for providing the facilities to conduct experiments on a Cary-14 spectrophotometer. They wish to express their thanks to Prof. S.Radhakrishna (I.I.T., Madras) and Prof. S.V. J.Lakshman (S.V. University) for thier interest in the work. The authors are grateful to the U.G.C. (India) for financial assistance.     

Canonical realizations of classical lie algebras

We construct sets of canonical realizations for all classical Lie algebras (A _n ,B _n ,C _n ,D _n ). These realizations depend ond parameters,d=1, 2, 3,...,n; all Casimir operators are realized by multiples of identity. For most of the real forms of these algebras we give sets of realizations which are, moreover, in well-defined sense skew-Hermitian. Further we study extremal cases of the presented realizations. The realizations with minimal numbers of canonical pairs are discussed from the point of view of general results concerning minimal realizations. On the other hand, a connection is found between our maximal realizations ofA _n and the Gel'fand-Kirillov Conjecture.The authors would like to thank Prof. A.Uhlmann for his kind interest in this work. They are very grateful to Prof. A. A.Kirillov and Prof. D. P.Zhelobenko for helpful discussions and to Prof. J.Dixmier for his informative letter concerning the problem mentioned in Sect. 5.One of the authors (W. L.) thanks Prof. I.Úlehla for the hospitality at the Nuclear Center of the Charles University, Praha.     

Measurements of the dependence of sonoluminescence on acoustic pressure of ultrasonic field and measurements of the acoustic spectrum of cavitation noise

Time-averaged values of the sonoluminescence in dependence on the acoustic pressure of ultrasonic field were measured in distilled water, exposed to ultrasonic field of frequency 43·40 kHz at temperatures of 5, 15, 25, 35 and 45 ° C in ambient atmospheric pressure. Average values of the sonoluminescence were measured with the aid of a photomultiplier — as a voltage drop on its working resistance. Effective acoustic pressure of ultrasonic field was measured with a piezoelectric s ensor coupled to a high-frequency millivoltmeter. The acoustic spectrum of cavitation noise (from 0·3 up to 2·0 MHz) in water was measured at temperatures of 5, 15, 25, 35 and 45 °C for various mean values of the sonoluminescence. Piezoelectric sensor was employed in detecting the spectrum of cavitation noise. The voltage signal on the sensor was measured by means of a heterodyne voltmeter. Sonoluminescence flashes were detected with a photomultiplier, amplified and displayed on an oscillograph screen together with the intensity of ultrasonic field in the liquid. Theoretical arguments are outlined explaining the occurrence of maxima in the acoustic spectrum of the cavitation noise.The authors express their thanks to Prof. RNDr. M.Brdika for his constant interest in their work and useful hints.     

A Mössbauer and X-ray diffraction study of nonstoichiometry in magnetite

The paper deals with the applicability of Mössbauer spectroscopy and X-ray diffraction methods for the determination of the deviation of magnetite from stoichiometry. The results show that among the data obtainable by both methods, the ratio of intensities of two partial spectra composing the Mössbauer spectrum of magnetite enables to evaluate the deviation of magnetite from stoichiometry quantitatively.The authors express their gratitude to Prof. Dr. Ing. J.Cirák who enabled them to perform all measurements of Mössbauer spectra at the Department of Nuclear Physics and Technics, Slovak Technical University, Bratislava. The authors are also indebted to Ing. P.Holba (Institute of Solid State Physics, Czechoslovak Academy of Sciences) and to Ing. Z.Drbálek (Research Institute of Sound and Picture) for the preparation of magnetite samples, and to Mr. P.Chaloupek (Faculty of Mathematics and Physics, Charles University, Praha) for computer calculation of lattice constants. The aid provided by members of the G. V. Akimov State Research Institute for the Protection of Materials, Dipl. Chem. K.Jendelová who carried out chemical analysis of the samples and Ing. K.Turecká who took part in X-ray diffraction measurements, is gratefully acknowledged.     

Study of magnetic interactions of the Fe2+ ions and the protons of crystallization water in FeSO4.n H2O hydrates

The paper deals with a study of interactions of protons in crystallization water of paramagnetic hydrates FeSO₄.n H₂O (wheren=1, 4, 5 and 7). The interaction of protons and paramagnetic ions Fe²⁺ and the nuclear dipole-dipole interaction of protons have been studied by means of the parameters expressing the dependence of the second moment of the proton nuclear magnetic resonance (NMR) spectrum on the external magnetic field, by means of the volume magnetic susceptibilities and the relaxation timesT ₁ of the investigated series of hydrates.We are grateful to Prof. Dr. hab. Z.Pajak, director of Department of Radiospectroscopy IF UAM in Poznan, and to his coworkers Dr. J.Kapturczak, Dr. K.Jurga, Dr. S.Glowinkowski and Mgr. F.Brych for facilitating our measurements mentioned in the paper as well as for a valuable discussion.     

Magnetic properties of crystalline boron

Magnetic properties of -rhombohedral boron are investigated measuring the temperature dependence of magnetic susceptibility. It was found that this dependence is similar to that of semiconducting glasses. An explanation of the dependence found is given and the concentration of dangling bonds is checked using thermodynamic consideration.The author thanks Prof. T.Niemyski for supplying the boron samples, Prof. L.Sosnowski and Dr. A.Zarba for valuable discussions and Mr. M.Klígl for technical assistance.     

On the spectrum of the F-centres in the neighbourhood of charged dislocations

Upon deformation of alkali halide crystals an electrical voltage can be observed between suitably placed electrodes due to the movement of charged dislocations. When the specimen is coloured, light induces electrical relaxation, the dislocation photoconduction. We analysed the spectrum of dislocation photoconduction as a spectrum of F-centres situated in the neigh-bourhood of charged dislocations. It is difficult to segregate the two competing effects on the F-spectrum, namely the electric and the strain field of the dislocation, so when we discussed our experimental data we had to assume that the change was caused by either the strain or the electric field. In this paper we discuss this problem theoretically by means of the method of moments. Comparing the expressions of the changes of the first and second moments for the strain field with the analogous ones for the Coulomb field of a charged dislocation jog we see that for every reasonable distance between the dislocation and the F-centre the effect of the strain field is the dominant one. The change of moments can be fitted to experimental data.The authors express their gratitude to I.Tarján and R.Voszka for their interest in this work and I.Gaál for his constructive criticism, he also directed our attention to the dislocation quadrupole field as to a possible third effect.     

Electronic spectrum of Cu2+ in rubidium magnesium sulphate hexahydrate

The single crystal electronic spectrum of Cu²⁺ in rubidium magnesium sulphate hexahydrate is interpreted in terms of the crystal field ofD _2h symmetry. From the EPR spectrum of the polycrystalline sample theg andA-values and hence the bonding parameter ( ²) are evaluated. Orbital reduction parameters are calculated by correlating the optical and EPR data.The authors wish to express their thanks to Prof. S. V. J. Lakshman for his interest in the work, and to UGC (India) for financial assistance.     

Hysteresis phenomena of the parametric oscillations

Parametric amplifiers have been described which are based on the magnetoelastic interaction of the oscillation of a torsional pendulum and an electrical circuit. When the inverting amplifier is driven overcritically, selfexcitation of the pendulum occurs. Because of the nonlinear magnetoelastic damping, it may happen that the pendulum oscillates only in a certain range of amplitudes. Varying the intensity of the magnetic pumping field, hysteresis effects of the oscillation appear which can be explained by damping measurements. Oscillation measurements of other authors can now be understood.The author thanks Prof. Dr. G.Dietz for many valuable remarks to this paper and Prof. Dr. H.Happ in whose institute the experiments were performed.     

Vavilov-Cherenkov radiation in the biaxial triglycine sulphate crystal

Some properties of the Vavilov-Cherenkov radiation in the biaxial triglycine sulphate crystal have been analysed. The radiation properties have been studied for the cases of protons moving along the main three dielectric axes. The measurements were performed with the 660 MeV proton beam.A quantitative agreement of experiment with Muziká's theoretical calculations on the directional properties was observed. In all the cases a qualitative agreement concerning azimuthal distribution of the radiation intensity of the extraordinary waves of both polarities as well as concerning the polarization properties predicted by Obdrálek's formulae has been obtained.Dedicated to the Memory of Professor . Muziká.On leave from Department of Nuclear Physics, Comenius University, Bratislava, Czechoslovakia.The authors are grateful to Prof. V. P.Dzhelepov, Director of the Laboratory of Nuclear Problems, to Prof. L. I.Lapidus for support of the experiment as well as to Prof. L. M.Belyaev and I. V.Gavrilova (the Institute of Crystallography of the USSR Academy of Sciences) for supplying triglycine sulphate crystals, to J.Obdrálek (Charles University, Prague) for fruitful discussions and helpful advice, to Dr. R.Pose for assistance in obtaining negative colour film, to E.Janikova and R.Janik for great assistance in the experiment.     

The role of effective two-nucleon potential in the electric monopole transition in C12 and O16

In the present paper the Shiff's model is used to explain the O⁺-transition mechanism in nuclei. In contrary to the Shiff's study more realistic effective potentials suggested bySiemens andSprung andBanerjee are applied. They give good results.The author would like to thank Prof. I.Úlehla and Z.Pluha for encouraging interest in this work.     

Very low temperature properties of bosons with repulsive core and attractive tails

The properties of a system of bosons interacting through a two body potential composed of a hard repulsive core followed by an attractive square well and having density of the order of that of liquid⁴He at the-point have been studied. The system is found to have a peculiar behaviour around 1 K and we assert that it may have undergone another phase transition around 1 K. Calculations on the effective mass show that them ^*/m values lie between 2 and 9 so that the interacting bosons may have a transition temperature below 1 K. We have also plottedE _k vs.k graph for temperatures below 1 K.The authors are thankful to Prof. F. C.Auluck, Dr. N. R.Ranganathan, Dr. H. G.Venkatesh and Dr. A. N.Phukan for helpful discussion. Authors thanks are due to Prof. B. R.Seth, D.Sc., F.N.A., Director, B.I.T., Mesra for constant encouragement. The authors thankfully acknowledge the financial assistance provided by the Indian National Science Academy, New Delhi.     

Electronic excitation spectrum of an antiferromagnetic semiconductor (EuTe)

We study the electronic quasiparticle spectrum of an antiferromagnetic semiconductor, with a special application to EuTe. By use of the commonly accepteds-f model it is shown that the conduction band splits into two quasiparticle subbands, where this splitting persists in the paramagnetic region (T>T _n ), too. Shape, width and degree of overlapping of the two subbands are strongly temperature dependent and quite different for different types off-spin arrangements.—We present furthermore a critical classification of mean field treatments (Zener model), which neglect all spin exchange processes between conduction electrons and localized moments. Within our many body approach the lower conduction band edge of EuTe does not shift significantly with temperature, in agreement with the experiment, while the Zener model predicts a drastic red shift upon cooling belowT _n .     

Thermodynamic theory of finite ferroelectric crystals with surface energy

The phenomenological Landau theory of phase transition is generalized to finite ferroelectric crystals with surface energy. Restrictions of the expansion imposed by the symmetry of the surface are considered, and further analysis is devoted to a special case. The solution in the approximation of constant polarization is discussed. Single domain states of a plate are analysed in greater detail.The authors are very grateful to Dr. V.Janovec and Dr. J.Fousek of the Czechoslovak Academy of Sciences for helpful discussions. Thanks are due to Prof. L.Valenta for the valuable discussions dealing with the magnetical analogical problem.     

Determination of electronic momentum densities and the Fermi surface of white tin by positron annihilation

Following the Mijnarends method, the momentum density distribution (p) of annihilation radiation in -Sn has been determined by unfolding the Mogensen and Trumpy experimental data. Some hypotheses concerning the shape of the -Sn Fermi surface as well as the characteristic structure of the strongly anisotropic enhancement factor are suggested.The authors wish to thank Dr. O.Mogensen and Prof. G.Trumpy for supplying their original experimental data. They are also grateful to Prof. S.Berko for many interesting and thoughtful remarks during the presentation of the work [9] at the Fourth Conference on Positron Annihilation.     

Present status of the experimental testing of the forward K+-p and pp, ¯pp dispersion relations

A brief survey of the present status of the experimental testing of the forward K^+-p and pp, pp dispersion relations is given. Some general questions concerning the experimental determination of the real part of the forward scattering amplitude are concerned. Recently developed forms of dispersion relations and of their substitutes are discussed.Presented by O.Dumbrajs at the Symposium on Hadron-Hadron Scattering at High Energies, Liblice, Czechoslovakia, June 16–21, 1975.On leave of absence from theInstitute of Nuclear Physics, Moscow State University, USSR We express our gratitude to the Organizing Committee of Symposium on Hadron Scattering at High Energies in Liblice, in particular to Prof. J.Fischer, for the oportunity to give this talk.We benefited very much from the creative atmosphere of the Symposium and from discussions, especially with Prof. G.Höhler.One of us (O.D.) acknowledges with gratitude the kind hospitality of the Warsaw University where these notes have been prepared.