Collisional deactivation of the isoelectronic 15N+2 A 2Πui (v=3) and CO+ A 2Πi (v=3 and 4) levels by helium atoms

Abstract

An optical–optical double resonance (OODR) technique is used to selectively populate rotational levels of the 15N+2 A 2Πui (v=3) state and monitor collision induced electronic transitions (CIET) to the X 2Σ+g (v=6 and 7) vibronic manifolds. The branching ratio from the A (v=3) state to the X (v=6 and 7) levels is determined experimentally and used in a phenomenological model based on past results. This ratio is used to determine the state specific collisional quenching rates from observed double exponential decay curves of the A (v=3) level. Similar results are obtained for CIET from the CO+ A 2Π (v=4) level to the X 2Σ+ (v=12 and 13) levels. In this case, the branching ratio from the A (v=4) level to the X (v=12 and 13) levels is not as accurate as for the 15N+2 case, but the result agrees with the empirical model, and state specific quenching rates are also determined from double exponential decay curves. In addition, the deactivation rate is determined for the CO+ A (v=3) level from its observed single exponential laser induced fluorescence curves. These new data for quenching of the CO+ A (v=3 and 4) states continues the trend of increasing quenching cross sections with increasing vibrational quantum number observed in previously published values for the A (v=0, 1, and 2) levels. A comparison is also made between rotational relaxation within the A (v=4) state and the abovementioned electronic deactivation in CO+. These results show that CIET in CO+ compares favorably to analogous experiments with its isoelectronic partners N+2 and CN, including energy gap and Franck–Condon factor dependencies. The collider in all cases is helium.