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Core vacancies created on opposite sides of a molecule operate against each other in polarizing the environment between them. Consequently, the relaxation energy associated with the simultaneous creation of these two core holes turns out to be smaller than the sum of the relaxation energies associated with each individual single core vacancy created independently. The corresponding residual, termed interatomic relaxation energy, is sensitive to the environment. In the present paper we explore how the interatomic relaxation energy depends on the length and type of carbon chains bridging two core ionized nitrile groups (-C≡N). We have uncovered several trends and discuss them with the help of simple electrostatic and quantum mechanical models. Namely, the absolute value of the interatomic relaxation energy depends strongly on the orbital hybridization in carbons being noticeably larger in conjugated chains (sp and sp2 hybridizations) possessing highly mobile electrons in delocalized π-type orbitals than in saturated chains (sp3 hybridization) where only σ bonds are available. The interatomic relaxation energy decreases monotonically with increasing chain length. The corresponding descent is determined by the energetics of the molecular bridge, in particular, by the HOMO-LUMO gap. The smallest HOMO-LUMO gap is found in molecules with the sp2-hybridized backbone. Here, the interatomic relaxation energy decreases slowest with the chain length. [ABSTRACT FROM AUTHOR]

Predissociation of H[sub 3] Rydberg states was investigated using the effective Hamiltonian which describes the vibronic transitions among the Rydberg states as well as the predissociation through the vibrationally excited 2s states. The motion of a Rydberg electron and the vibrations of the H[sup +][sub 3] ion core was treated simultaneously without assuming the Born-Oppenheimer approximation. We developed the effective potential for a Rydberg electron, which contains the Coulomb potential and the exchange effect. The energies and predissociation lifetimes of H[sub 3] Rydberg states were obtained by analyzing the effective Hamiltonian and compared with the available experimental values. The s and p Rydberg states with lower vibrational excitation have lifetimes between a few ps to 1 ns and show an irregular lifetime distribution with respect to the principal quantum number. In contrast, d and ƒ Rydberg states have longer lifetime, 10 ns for example. The energy level spacings of the Rydberg states obey the distribution close to the Poisson one and thus indicates these states being regular. The route of predissociation was investigated by propagating a wave packet as well as analyzing the eigenvectors of the effective Hamiltonian. We found that the energy level matching between nearby states play an important role for efficient predissociation. The present results suggest that the predissociation of the H[sub 3] molecule and the dissociative recombination of the H[sup +][sub 3] ion might be efficient under rotational excitation through inclusion of additional energy levels. [ABSTRACT FROM AUTHOR]

We present the results of an experimental and theoretical investigation of vibrationally resolved valence shell photoionization of BF3 leading to the [image omitted] state of [image omitted], where vibronic coupling and shape resonances are known to be important. The experimental vibrational branching ratios for multiple quantum excitations of the symmetric stretching mode of the ion [image omitted] as well as for the single vibrational excitation of the asymmetric stretching mode [image omitted] are compared with the predictions of single-channel Schwinger variational calculations performed within the Chase adiabatic approximation to obtain vibrational-state specific cross sections. The presence of a shape resonance in the continuum of [image omitted] symmetry is seen to lead to significant non-Franck-Condon intrachannel vibronic coupling effects. The breakdown in the Franck-Condon approximation is due to the sensitivity to the asymmetric stretching mode of the energy of the resonance and the magnitude of the transition moment for exciting the resonance. However, there are indications that interchannel vibronic coupling effects may also be significant in this system. [ABSTRACT FROM AUTHOR]