Collision induced electronic energy transfer between the A 2∏u i (v=4) and X 2∑+g (v=8) rotational manifolds of N+2

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Abstract
A two laser, optical–optical double resonance technique has been used as a direct probe of the electronic energy transfer process between the A 2∏ui (v=4) and X 2∑+g (v=8) rotational manifolds of 14N+2. For the first time collisional selection or propensity rules are obtained for a homonuclear molecule which has no perturbations or ‘‘gates’’ between the states involved. The selection rules s→s, a→a, and s⇄a are shown to apply for this electronic energy transfer process. The transfer rate is shown to be comparable to that for rotational energy transfer and in spite of the competition between these two mechanisms it is demonstrated that there is a propensity towards ΔJ≊0 rather than ΔE (energy gap) ≊0. These selection or propensity rules are optical‐like and appear to result from collision induced electric dipole transitions. Therefore, these are truly electronic energy transfer processes rather than a form of rotational energy transfer as occurs when the rotational levels are known to be perturbed in the free molecule.