Quantum scattering study of collisional energy transfer in He+NO2: The importance of the vibronic mixing

Abstract

We present the results of a quantum scattering study of collisional energy transfer in the title reaction, considering energies up to 14000 cm-1 above the NO2 zero point energy. The collisions are described using the VCC-IOS (vibrational-coupled-channel infinite-order-sudden) quantum scattering method, with two coupled potential surfaces and as many as 329 total states in the basis expansion. The intramolecular potentials describe the X2A′(2A1) and A2A′(2B2) states of NO2, and their coupling through a conical intersection. The intermolecular potential is based on empirical sums of atom-atom potentials. We find that vibronic mixing between the X and A states of NO2 strongly enhances collisional energy transfer and, as a result, there is a noticeable change in the energy transfer efficiency as vibronic energy in NO2 is increased above the threshold for A state excitation. This change in efficiency occurs even if the same intermolecular potential is used for both NO2 electronic states. Many transitions are enhanced because the energy gaps between vibronically mixed and unmixed states are smaller. Energy transfer is also enhanced between states which are both vibronically mixed, whenever a significant component of each state involves the same zeroth order level of the excited electronic state. The calculated results are in good agreement with recent measurements. © 2000 American Institute of Physics.