Radiative and radiationless vibronic deactivation rates in selectively excited CO+

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Abstract
A tunable dye laser has been used to selectively excite particular (v=0–3) vibrational levels of A 2Π CO+. The CO+ is produced in a He bath by Penning ionization of CO by He metastables. By studying the time resolved emission of CO+ from selected vibrational levels as a function of He pressure, values have been obtained for the radiative decay rates and the velocity averaged cross-sections for CO+ vibrational relaxation upon He collision. The cross sections are all rather large (≳0.1 Å2) and increase considerably with increasing v. Time resolved spectra of the vibrationally relaxed emission require the postulation of a three-level system to fit their form. It is proposed that both of these effects are consistent with a vibrational relaxation mechanism wherein the A 2Π CO+ vibrational levels relax via intermediate, highly excited, vibrational levels of the ground X 2Σ state of CO+.