A joint experimental and theoretical study of A 2Π→X 2Σ+ electronic energy transfer in the CN molecule induced by collisions with helium

In this paper, we report an experimental and theoretical reinvestigation of the electronic quenching of CN(A 2Π) induced by collisions with He, concentrating on transitions from individual rotational-fine-structure levels of the vA=7 manifold into individual levels of the energetically nearby vX=11 manifold. Experimental cross sections are obtained by an optical–optical double resonance (OODR) technique. Simultaneously, for the first time, the small non-Born–Oppenheimer mixing between the A 2Π and X 2Σ+ states of the isolated CN molecule is included in the quantum scattering calculations. The presence of these terms results in a significant enhancement in the electronically inelastic cross sections, but only in the vicinity of the electronic ‘‘gateways,’’ where the perturbational mixing is largest. There is reasonable agreement between the experimental and calculated final state distributions.