Symmetries, propensity rules, and alternation intensity in the rotational spectrum of N2 (C 3Πu) excited by metastables Ar(3P0,2)

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Abstract
We have obtained high resolution spectra N2(C 3Πu→B 3Πg) afterglow fluorescence resulting from excitation transfer from state selected Ar metastable 3P0 or 3P2. This was achieved by selective depopulation of one metastable by optical pumping using a tunable c.w. dye laser. Relative probabilities of excitation of well defined rotational, spin, and parity molecular Λ doublet substates were obtained for reaction of 14N2 and isotopic 15N2 with Ar*(3P2) and Ar*(3P0). A semiclassical model is proposed and found in fairly good agreement with the observed relative yields. The physical bases of the model are justified and imply that (a) spin–orbit interactions are effective during the collision, (b) the plane of rotation of the excited N2 molecule is a plane of symmetry, (c) Λ doublet c states are preferentially populated in the excitation transfer process.