[en] A striking feature of recent measurements of the photoionization of H₂(C¹Pi/sub u/) is that the distribution of final vibrational states of H₂⁺ differs significantly from the predictions of the Franck-Condon approximation. A theory is presented that accounts for these measurements. The essential physical mechanism is photoexcitation of the dissociating, autoionizing ¹Pi/sub g/ electronic state of H₂, followed by competition between dissociation of the nuclei (leading to H/sup */+H) and electronic autoionization (leading to H₂⁺+e)

[en] Some aspects of the unified Franck-Condon approximation to the line shape theory are discussed. Recent attempts to interpret the behaviour of profiles in the line wings are reviewed

[en] Similarities between the Franck-Condon effect and the concept of Squeezed States have been advanced as a conjecture in the past, or noticed as a marginal fact, without giving a full explanation of how these two important concepts are connected. In this work the authors outline a unifying formulation that contains as special cases both phenomena. The power of the new approach is shown in a general formula from which all particular cases can be derived

No abstract available

[en] Franck-Condon factors govern intensity or product distributions in many radiation- or collision-induced phenomena. The subject of this paper is the range and nature of the Franck-Condon distribution. Mainly the electronic transitions in diatomic molecules are considered. It is concluded that the primitive semiclassical treatment of Franck-Condon overlap integrals unifies the classical and quantum version of the Franck-Condon Principle. The stationary phase approximation tells us that these integrals accumulate mainly around the classical transition points. The difference potential is important in modern classical methods to be used for the approximate calculation of electronic spectra of polyatomic molecules, and leads to a simplification of tedious calculations through near-exact sum rules. (G.Q.)

No abstract available

[en] Compete text of publication follows. Proton collision with the CH radical is interesting as a benchmark system to check approximations that can be applied to collisions with larger molecules, which are relevant in radiation damage of biological systems. The aim of the present work was to check the validity of several approximations. In particular calculation at the Franck-Condon (FC) level was compared with more accurate calculations that employ the sudden approximation for rotation and vibration. We also discussed the extension of the calculation to energies below 50 eV. The ab initio study of ion-molecule collisions at low and intermediate energies is carried out by employing a molecular expansion. This method requires the calculation of potential energy surfaces and dynamical couplings of the supermolecule formed during the collision, which was carried out by means of quantum chemistry techniques implemented in MOLPRO. We have calculated total charge transfer cross sections with a fixed molecular orientation (θ = 60 deg)¹ and a 2-state basis (3²A', 4²A'). The eikonal calculation included both radial and rotational couplings, while only the radial coupling was included in the quantum mechanical calculation. Our results point out that the eikonal treatment is appropriate in the energy of this work. Besides, the approximation of neglecting the rotational coupling does not significantly modifies the total cross section. While the change of the cross section with p is relatively small for v > 0.1 a.u. (E ∼ 250 eV), at lower velocities the energy difference becomes critical and we obtain very large cross sections for p < 1.9 a.u. where the two states are quasidegenerate in the limit R → ∞. Although for v < 0.1 a.u. the results of FC and sudden vibrational approximation agree, the strong dependence of the cross section on p indicates that the approximation is probably not accurate. In this respect, the decrease of the cross section at low velocities, which was also found in H₃⁺, might be a consequence of the neglect of a vibronic resonant mechanism similar to that found in Ref. [5]. In practice, the extension of the present calculation to E < 250 eV would require the use of regularized states and the use of a vibronic expansion. Acknowledgements. This work was supported by the Hungarian OTKA Grant No.K73703.

[en] Resonant Raman response of impurity molecules in nonmetallic solid matrix is solved exactly. The model embodies the nonradiative interaction between impurity molecule and the nearest-neighbour molecules in the solid. The interatomic vibration of the excited electronic level of the molecule is modelled by harmonic and anharmonic potential. Frank-Condom and anharmonic effects are discussed by selected numerical examples

[en] We introduce a set of conditions to be satisfied by natural collision coordinates in order to enable the nonseparable multidimensional bound-continuum Franck--Condon integrals, arising in the quantum theory of collinear polyatomic dissociation processes, to be reduced to one-dimensional integrals. Because these conditions are not satisfied by available natural collision coordinate schemes, we investigate, in detail, the nature of one set of coordinates which satisfies these conditions. It is demonstrated that these coordinates can be chosen to faithfully represent the asymptotic motions of the fragments as well as the motion of the fragments in the Franck--Condon region on the repulsive electronic surface. The kinetic energy operator is displayed as an explicit function of the repulsive surface coordinates. The half-collision boundary conditions are described in a fashion to enable numerical computations of the continuum functions along the reaction coordinate

No abstract available