Transfer of Electronic Energy between a Metastable Argon Atom and a Nitrogen Molecule

Abstract

A detailed study has been made of the mechanism of electronic energy transfer between a metastable argon atom and a nitrogen molecule. The transition involves the excitation of nitrogen to the C3Π state. The metastable energy of argon is sufficient to excite the v′ = 2 level of the C3Π state if the nitrogen is originally in its v″ = 0 vibrational level of the X1Σ state. It was found that (1) the v′ = 3 level was not excited, (2) the population of the v′ = 0 level was greatly enhanced with the excess energy going into rotational energy of the N2 molecule, (3) the relative intensities of the v′ = 0, 1, and 2 levels could not be predicted on the basis of the Franck—Condon factors, and (4) the collision cross section for the observed energy transfer is about 100 times greater than the argon—argon de-excitation cross section. It is shown that the enhanced rotational structure of the v′ = 0 level of the C3Π state can be explained from the viewpoint of a minimum amount of initial internal energy transferring to relative kinetic energy of the particles. The v′ = 1 and 2 levels did not show enhanced rotational structure. From a consideration of the carbon monoxide—argon system, it is shown that the Wigner spin-conservation rule governs the efficiency of the electronic energy transfer during collision. This condition applies regardless of whether or not the transitions are optically allowed.