Knowledge Bank

A slit-jet discharge nozzle has been constructed to investigate jet-cooled molecular ions with direct absorption infrared spectroscopy. As a first test of the discharge source rovibrational spectra of two protonated ions, $H3O+$ and $HN^{+}$42, generated in a pulsed slit-jet expansion have been studied using a narrow band (2 MHz) IR difference frequency laser in the 3 $\mu$m region. Extensive cooling of the nascent molecular ions is produced by the supersonic expansion as demonstrated by a 25 K rotational Boltzmann plot for $HN2+$ in a Ne expansion. The low temperature and ""collision free"" environment provided by the supersonic expansion has two desired effects: (I) it serves to stabilize the gas-phase molecular ions and (ii) it increases the sensitivity of the technique by significantly narrowing the transition lineshape. Worke is currently aimed at exploiting the dynamics of ion formation at very low temperatures to study small molecular ions and molecular ion clusters; the most recent results will be presented.