Articles you may be interested inIon-pair dissociation dynamics of O2 in the range 17.2-17.5 eV studied by XUV laser and velocity map imaging method State-to-state photodissociation dynamics of OH radical via the A 2 Σ + state: Fine-structure distributions of the O ( 3 P J ) product Parallel and perpendicular components of the Herzberg I, II, and III transitions contribute to the photodissociation of O 2 in the Herzberg continuum. The photodissociation dynamics determines the O( 3 P j ), jϭ0,1, and 2 atomic fine-structure branching ratios and angular distributions, which were determined in ion imaging experiments at ϭ236, 226, and 204 nm by Buijsse et al. ͓J. Chem. Phys. 108, 7229 ͑1998͔͒. In the preceding paper we presented potential energy curves for all eight ungerade O 2 states that correlate with the O( 3 P)ϩO( 3 P) dissociation limit, and the R-dependent spin-orbit and the nonadiabatic radial derivative couplings between these states. Here, we employ these potentials and couplings in a semiclassical calculation of the fine-structure branching ratios, atomic polarizations, and fine-structure resolved anisotropy parameters. We discuss the adiabaticity of the dissociation by comparing the results with adiabatic and diabatic models. The O( 3 P j ) 2ϩ1 REMPI detection scheme used in the experiment is sensitive to the polarization of the atomic fragments. We predict an important effect of the polarization on the anisotropy of the jϭ1 and jϭ2 ion images at low energies ͑Ͼ236 nm͒. The agreement between the semiclassical calculations and experiment is reasonable, possible explanations for the remaining differences are discussed.
Ab initio theoretical studies of potential energy surfaces in the photodissociation of the vinyl radical. I. Ã state dissociationWe present ab initio complete active space self-consistent-field plus multireference configuration interaction ͑CASSCFϩMRCI͒ potential energy curves for the eight electronically excited ungerade states of oxygen (A ϩ ) that correlate with the O( 3 P)ϩO( 3 P) dissociation limit. We also report the R-dependent spin-orbit couplings between these states and the R-dependent radial derivative coupling matrix element ͗2 3 ⌺ uThe near degeneracy in the long range of the same-symmetry states 2 3 ⌺ u ϩ and A 3 ⌺ u ϩ may result in unphysical mixing of these states in a CASSCF calculation. We derive the correct asymptotic behavior of these states as dictated by the quadrupole-quadrupole interaction and we show how a correct long range description of these states can be achieved numerically by employing undistorted molecular orbitals. Bound state calculations using Herzberg I, II, and III potentials show excellent agreement with all available spectroscopic data. In the accompanying paper the potentials and couplings will be employed in a semiclassical study of the photodissociation of O 2 in the Herzberg continuum.
Vibrational Herzberg bands of the O 2 molecule just below its first O( 3 P)ϩO( 3 P) dissociation limit are since long-known to be perturbed. Jenouvrier et al. ͓J. Mol. Spectrosc. 198, 136 ͑1999͔͒ assigned the cause of the perturbations to five vibrational levels supported by the shallow minimum in the 1 3 ⌸ u potential energy curve around 5.5a 0 . Using ab initio potential energy curves and spin-orbit couplings from previous work ͓J. Chem. Phys. 116, 1954 ͑2002͔͒ we present a full quantum calculation of all ungerade rotation-vibration-electronic states of oxygen just below the dissociation threshold, through a total angular momentum quantum number of Jϭ19. This calculation shows that the original assignment, based on a Hund's case ͑a͒ model of a regular 1 3 ⌸ u multiplet was not correct. Based on our calculation we present a new assignment of the perturbing states: 1 3 ⌸ u,⍀ϭ2 (vϭ0͒, 1 3 ⌸ u,1 ͑0͒, 1 3 ⌸ u,2 ͑1͒, 1 3 ⌸ u,1 ͑1͒, and 1 3 ⌸ u,0 Ϫ͑0͒ in order of ascending term values. We show the new assignment to be consistent with experimental data and we also propose new spectroscopic parameters for the perturbing states.
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