High Resolution Spectroscopy of Ti2 and AlY at Near-Infrared Frequencies

High resolution jet-cooled molecular beam spectroscopy has been effective in revealing the bonding between transition metals. One periodic trend that has developed during the study of small transition metal molecules is the relatively weak bond strength in the early 3d transition metals (Sc2, Ti2 in comparison to middle (V2, Cr2) or late (Ni2, Cu2) members of the 3d series. This trend of bond strengths in early transition metals is not so pronounced in the 4d and 5d metals where d-bonding is a major contributor to molecular stability. Low bond strengths in molecules, whether due to poor d overlap or high s ← d promotion energy, provides a challenge to the spectroscopist. It has been shown that diatomic systems with a large density of electronic states, as is usually the case for open d-subshell molecules, undergo a rapid predissociation (τ < 5 ns) when excited above the lowest dissociation limit.1 The extreme density of states responsible for predissociation also precludes isolation of single rovibronic states suitable for high resolution spectroscopy at energies near the dissociation limit of these molecules. The spectroscopist interested in investigating species with low bond strengths and high densities of electronic states, as in our investigation of Ti2 and AlY, is forced to search the low energy near-infrared region for isolated electronic states that are not hopelessly perturbed. In the present near-infrared investigation of Ti2 and AlY we have employed resonant two photon ionization (R2PI) as the detection strategy for obtaining optical spectra in a jet-cooled molecular beam.