Molecular-beam study of the collisional intramolecular coupling of N2(<i>B</i> 3Π<i>g</i>) with the N2(<i>A</i> 3Σ+<i>u</i>) and N2(<i>W</i> 3Δ<i>u</i>) states

Abstract

Collision-induced intramolecular energy transfer between N2 triplet states has been investigated for the first time under single-collision conditions. A beam containing N2 molecules in the long-lived N2(A 3Σ+u) and N2(W 3Δu) states interacted with target particles (H2, N2, NO, and all rare gases) either in a collision cell or in a secondary, pulsed molecular beam. From the collision region N2(B 3Πg) emission was observed with a linear dependence on the target-gas density. It is due to collision-induced intramolecular energy transfer (‘‘collisional coupling’’) N2(W→B) and N2(A→B). These two contributions were differentiated by means of data taken at different distances from the beam source, using the known radiative rate decay of N2(W). The spectra (40 Å full width at half maximum) show clearly the importance of energy resonance between reactant and product vibrational levels, with an exponentially decreasing dependence of the cross section on the energy mismatch. Relative cross sections were obtained for all collision partners and the B-state vibrational levels v′=3–10. For the W→B collisional coupling, absolute cross sections were derived by relating the intensity of the collision-induced luminescence to that of the collisionless beam afterglow, which is also due to the N2(W) species and was studied previously.