15min:
THE ASYMPTOTIC REGIONS OF THE POTENTIAL ENERGY SURFACES RELEVANT FOR THE O(3P) + O2(X3 Sigma-g) ^\rightharpoonup_\leftharpoondown O3, O(3P) + SO(X3 Sigma-) ^\rightharpoonup_\leftharpoondown SO2 REACTIONS.

ISABELLE NAVIZET AND PAVEL ROSMUS, Laboratoire de Chimie Théorique, Université de Marne la Vallée, F 77454 - Champs sur Marne, France.

The photodissociation dynamics and formation of sulfur dioxide and ozone, important trace species in the atmosphere, have been subjected to many studies over the past decades. The long range potential energy functions including spin-orbit couplings for all states correlating with the lowest asymptote of the reactions O(3P) + X ( X stays for O2(X3 Sigma-g) or SO(X3 Sigma-) have been calculated using highly correlated electronic wavefunctions. While the cluster of Sigma states lie above the Pi states for linear ozone, it is more complicated for linear SO2. The two orientations SO...O and O...SO lead to different reaction profiles. For SO...O orientation, the potential energy surfaces (PES's) resemble to O...O2 approach, the Sigma states lie above the Pi states for large R_(SO...O) distances. In the O...SO approach, Pi states lie above the Sigma states at the asymptote and crossings occur at small distances.

For bent geometries, the Pi states split into Renner-Teller components with A' and A" symmetry, respectively. For ozone, the different Pi spin multiplets cross for valence angles around 160o and the 1A' component leading to X1A1 state becomes the lowest one. The calculations of the matrix elements of the spin-orbit operator show that for valence angles around 160o and close to 90o the mixing among the singlet, triplet and quintet states is strong and the electron spin quantum number is no longer a good quantum number. The potential energy functions of SO2 are much more complex than previously reported due to similar couplings. This implies that the reaction dynamics for both reactions can not be treated by using a single adiabatic PES.