Singletndash;triplet surface crossings and lowhyphen;temperature rate enhancement for O(3P)+H2rarr;OH+H

摘要

Lowhyphen;temperature curvature in Arrhenius plots of Hhyphen;atom transfer reactions is usually attributed to tunneling. This paper investigates the feasibility of an alternative mechanism involving nonadiabatic transitions to enhance the lowhyphen;Trate of O(3P)+H2rarr;OH+H.3APrime; and1Aprime; potential surfaces are calculated for the configuration OHH over a range of bond angles. Theab initiosurface calculations use two basis sets: doublehyphen;zeta + polarization (DZP), and DZP augmented by bond functions and Rydberg orbitals (BF), followed by extensive configuration interaction. The CI data points are fitted by a rotated Morse curvehyphen;cubic spline functional form. The surface crossing is analyzed in detail. The singlet surface crosses the triplet surface near 120deg; at an energy which is slightly above (2 kcal/mol) the energy of the lowest triplet barrier (13.2 kcal/mol for the linear geometry). The implications for lowhyphen;temperature kinetics are discussed.