Propensities for collision induced electronic transitions in a diatomic molecule

Abstract

An optical–optical double resonance (OODR) technique is used to determine propensities for collision induced electronic relaxation by helium atoms from a specific A 2Πui (v=4, J) rotational level to the X 2Σ+g (v=7) manifold of N+2. The propensities for collisional transfer from this specific level to the nearly degenerate (∼0.04 cm−1 separation) spin components of the X(v=7) state are resolved by scanning the probe laser through the B 2Σ+u –X 2Σ+g (5,7) band whose upper state is perturbed. Although ΔJ≈0 transfers are preferred, the results show the propensities to be quite different and strongly dependent on the A(v=4,J) level initially populated by the pump laser. The observation of these propensities for collisional electronic energy transfer through a large energy gap of approximately 1760 cm−1 demonstrates the remarkable fact that this process occurs as fast or faster than rotational energy transfer through gaps of ∼10 cm−1. These results are found to be in qualitative agreement with theoretical relative cross sections derived by Alexander and Corey for inelastic collision induced transitions between 2Π and 2Σ electronic states of a diatomic molecule.