Knowledge Bank

We have developed a highly sensitive detection scheme for weak vibrational overtone $transitions1$. After overtone excitation of a light atom stretch, we use $CO2$ laser multiphoton excitation to dissociate only the vibrationally excited molecules. The overtone transition is then monitored by detecting the dissociation fragments by LIF. By scanning the overtone excitation laser and using LIF to monitor the dissociation fragments, we obtain an excitation spectrum that is identical to the vibrational overtone absorption spectrum. The sensitivity of this new detection scheme is sufficient to observe vibrational overtone transitions in collisionless environments such as low pressure gas cells and free jet expansions. This new detection scheme and vibrational overtone spectra of jet cooled methanol and methanol-$d3$ will be presented.