Electronic fine structure transitions and rotational energy transfer of NO(<i>X</i> 2Π) in collisions with He: A counterpropagating beam study

Abstract

The collision dynamics of NO(X 2Π) with He is investigated at a collision energy of 147 meV using the method of counterpropagating pulsed molecular beam scattering. One-dimensional product velocity distributions are determined through ion time-of-flight analysis. State specific detection of NO is achieved through (2+1) resonance enhanced multiphoton ionization detection via the E 2Σ+ intermediate state. Calculated frequencies and line strength factors for the two-photon transition enable the extraction of state resolved degeneracy averaged integral and differential cross sections. The overall behavior of the integral cross sections for fine structure conserving and changing transitions, weighted by the degeneracy of the final state, is well described by two different exponential energy gap laws. Differential cross sections for both types of transitions exhibit very different rotational rainbow structures. For the multiplet changing transition, the scaling law suggests an increased energy transfer efficiency while the rotational rainbow structure indicates a larger effective anisotropy. Therefore, the dynamics at the probed collision energy is clearly dominated by fine structure changing collisions when magnetic sublevel specific cross sections for a specified energy transfer are compared.