Accurate quantum mechanical calculations of differential and integral cross sections and rate constant for the reaction using an ab initio potential energy surface

New ab initio studies of the OH(A(2)Σ(+))-Kr system reveal significantly deeper potential energy wells than previously believed, particularly for the linear configuration in which Kr is bound to the oxygen atom side of OH(A(2)Σ(+)). In spite of this difference with previous work, bound state calculations based on a new RCCSD(T) potential energy surface yield an energy level structure in reasonable accord with previous studies. However, the new calculations suggest the need for a reassignment of the vibrational levels of the electronically excited complex. Quantum mechanical and quasi-classical trajectory scattering calculations are also performed on the new potential energy surface. New experimental measurements of rotational inelastic scattering cross sections are reported, obtained using Zeeman quantum beat spectroscopy. The values of the rotational energy transfer cross sections measured experimentally are in good agreement with those derived from the dynamical calculations on the new adiabatic potential energy surface.

To assess the relative reactivity of the spin-orbit excited state of atomic Cl with molecular hydrogen, we have measured differential cross sections using an atomic Cl beam with a known concentration of the ground and excited spin-orbit states. These are compared with the first determination of the cross sections from quantum mechanical scattering calculations on a set of coupled ab initio potential energy surfaces. The comparison suggests that these surfaces may underestimate the degree of rotational excitation of the HCl products and that the excited spin-orbit state plays a minor role in the reaction.

It is proposed that the two Λ-doublet levels of linear molecules with nonzero electronic orbital angular momentum be labeled Λ(A′) and Λ(A″), e.g., Π(A′) and Π(A″) for Π states, etc., according to the following prescription: All series of levels in which the electronic wave function at high  J is symmetric with reflection of the spatial coordinates of the electrons in the plane of rotation will be designated Λ(A′) for all values of J, and all those for which the electronic wave function is antisymmetric with respect to reflection will be denoted Λ(A″). It is emphasized that this notation is meant to supplement, and not replace, the accepted spectroscopic e/f labeling and the parity quantum number. The utility of the Λ(A′)/Λ(A″) notation is that it is of most relevance in the mechanistic interpretation of reactive or photodissociative processes involving open-shell molecules.

Inelastic collisions of OH(X 2Π)+Ar at an energy of 746 cm−1 have been studied in a crossed molecular beam experiment. The OH(X 2Π) radicals were prepared in the v=0, Ω=32, J=32, f state by hexapole state selection. Parity-resolved integral state-to-state cross sections for rotational excitation have been determined up to the Ω=32, J=92 and Ω=12, J=52 states. A strong preference is found for spin–orbit manifold conserving transitions to final states of e symmetry. The experimental results are compared to quantum scattering calculations on ab initio potential energy surfaces developed by Degli-Esposti and Werner [J. Chem. Phys. 93, 3351 (1990)] and by Klos et al. [J. Chem. Phys. 112, 4952 (2000)]. The overall agreement between experiment and theory is very good; however, the calculated cross sections for spin–orbit changing transitions are a bit larger than the experimental values. The results are also compared to previous experiments at a collision energy of 451 cm−1.