Investigation of lattice dynamics by means of vibronic spectra

Electronic transitions at a foreign probe ion in a lattice exhibit vibrational sidebands. They may be used as a new tool to investigate lattice dynamics. To make this too effective the theory of vibronic spectra has been refined. The principal refinement is that of a partial Born-Oppenheimer approximation which establishes a rigid coupling of the electronic wavefunctions of the foreign ion to its own nucleus. The structural form of the one-phonon sideband is given as a projection of the classical Greens' function (imaginary part) onto single multipole-fields in lattice space. Employing a variety of electronic transitions and by careful group-theoretical analysis a complete irreducible sequence of projections can be extracted from the experiments. These functional forms depend sensibly on the eigenvectors of the lattice modes, whence they contain information, which cannot be received from neutron scattering. Moreover, the spectra related to the higher multipoles give insight into the disturbed (local) dynamics, whereas the lower type spectra concern the undisturbed (ideal) one. Systems, where the foreign probe ion has high symmetry, are most suitable for the new method. For systems of low local symmetry approximations are suggested by the low-frequency behaviour of the measured one-phonon band. Because of the high resolution of optical measurements, the information from vibronic spectra is comparable or even superior in detailed richness to neutron scattering data.     

Dynamical treatment of quenching-factors (Ham-factors) for the linear E-e Jahn-teller problem

The quenching factors for the linear E-e Jahn-Teller system are calculated by use of the exponential transformation method. In the extremal coupling cases the results are identical with those of Ham [1] and others [2]. For intermediate interactions, however, the factors p and q do not exhibit a monotonic overall decrease with increasing coupling strength, as suggested by Ham. Instead, both p and q have a minimum. In addition, p crosses the zero axis for λ ≌ 0.66.     

Zum Nachweis von 8-Oxychinolin im Bauch

Ohne Zusammenfassung     

Azotometrische Bestimmung von Penicillin

Ohne Zusammenfassung     

Ein neues Verfahren zur Bestimmung kleiner Mengen von quatern?ren Ammoniumverbindungen

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Soft modes in semiconducting SrTiO3

The temperature and concentration dependence of the soft zone boundary mode in heavily reduced SrTiO₃ was studied by means of inelastic neutron scattering. It was found that the 105 K structural phase transition is suppressed completely for about 2% oxygen vacancies. The results are discussed in terms of recent models.