VIBRATIONAL RELAXATION IN THE $CO^{+}$ MOLECULAR ION

Abstract

Ground state $X^{2} \Sigma^{+}\; CO^{+}$ molecular ions have been produced in a thermal He bath by Penning ionization of CO by He metastables. Specific rovibronic levels of the $A^{2} \Pi$ state of $CO^{+}$ have been excited by a tunable dye laser. Observation of the time-resolved laser-induced fluorescence allows the determination of the upper level lifetime as a function of He pressure. Radiative lifetimes and cross-sections for radiationless relaxation via He-$CO^{+}$ collisions are deduced for the v = 0-3 levels. The cross-sections are surprisingly large. Observations of laser-induced fluorescence from levels other than that initially excited indicates that relaxation between adjacent vibrational levels of the $A^{2}\Pi$ state is not direct. It is postulated that it may involve high vibrational levels of the ground $X^{2} \Sigma^{+}$ state.