Analogue of oscillation theorem for nonadiabatic diatomic states: application to the A (1)Sigma(+) and b (3)Pi states of KCs.

Relative intensity measurements in the high resolution A (1)Sigma(+) approximately b (3)Pi--> X (1)Sigma(+) laser induced fluorescence spectra of the KCs molecule highlighted a breakdown of the conventional one-dimensional oscillation theorem (L. D. Landau and E. M. Lifshitz, Quantum Mechanics, Pergamon, New York, 1965). For strongly spin-orbit coupled A (1)Sigma(+) and b (3)Pi states the number of nodes n(A) and n(b) of the non-adiabatic vibrational eigenfunctions phi and phi corresponding to the v-th eigenstate differs essentially from their adiabatic counterparts. It is found, however, that in the general case of two-component states with wavefunctions phi and phi coupled by the sign-constant potential operator V(12) not equal 0: (1) the lowest state v = 0 is not degenerate; and (2) the arithmetic mean of the number of nodes n(1) and n(2) of phi and phi never exceeds the ordering number v of eigenstate: (n(1) + n(2))/2

Structure and dynamics of acrolein in (1,3)(pi,pi*) excited electronic states: a quantum-chemical study.

The geometrical structure, conformer energy differences, and conformational and vibrational dynamics of acrolein in (1,3)(pi,pi(*)) electronic states were investigated using a number of single- and multi-reference quantum-chemical methods. Peculiarities of acrolein in the (1)(pi,pi(*)) state were described with both conformers being significantly non-planar. A Valence Focal-Point Analysis of the conformer energy difference in the (3)(pi,pi(*)) state was performed. The coupling of the internal rotation about C-C and C=C bonds with large amplitude molecular motions, such as non-planar distortions of carbonyl, methylene, and methyne fragments was also investigated. The corresponding two-dimensional PES sections were constructed.

Vibrational spectra and ab initio analysis of tert-butyl, trimethylsilyl, trimethylgermyl, trimethylstannyl, and trimethylplumbyl derivatives of 3,3-dimethylcyclopropene X. Some regularities.

The changes in the vibrational frequencies of 1-tert-butyl and 1,2-di-tert-butyl derivatives of 3,3-dimethylcyclopropene brought about by substitution of the central carbon atom (X) of the tert-butyl moieties by Si, Ge, Sn, or Pb atoms are examined. The most important decrease in the vibrational frequencies implicating the X(CH(3))(3) moieties is noted for substitution of X=C by Si. The substitutions of Si by Ge or Ge by Sn or Sn by Pb are not accompanied by the pronounced frequency shifts observed for the C-->Si transition. An explanation is given for trends in these vibrational frequencies for the transitions X=C-->Si-->Ge-->Sn-->Pb. It is concluded that there are lower limiting values of the vibrational frequencies of a molecular moiety which are approached when the mass of its isovalent atom is increased. This leads to the formation of cluster regions in the vibrational spectra for the frequencies of the SnC(3) and PbC(3) moieties.