State-to-State Reaction Dynamics of ¹⁸O+³²O₂ Studied by a Time-Dependent Quantum Wavepacket Method

The title isotope exchange reaction was studied by converged time-dependent wave packet calculations, where an efficient 4th order split operator was applied to propagate the initial wave packet. State-to-state differential and integral cross sections up to the collision energy of 0.35 eV were obtained with ³² O ₂ in the hypothetical j ₀ = 0 state. It is discovered that the differential cross sections are largely forward biased in the studied collision energy range, due to the fact that there is a considerable part of the reaction occurring with large impact parameter and short lifetime relative to the rotational period of the intermediate complex. the oscillations of the forward scattering amplitude as a function of collision energy, which result from coherent contribution of adjacent resonances, may be a sensitive probe for examining the quality of the underlying potential energy surface. a good agreement between the theoretical and recent experimental integral and differential cross sections at collision energy of 7.3 kcal/mol is obtained. However, the theoretical results predict slightly too much forward scattering and colder rotational distributions than the experimental observations at collision energy of 5.7 kcal/mol.