ROTATIONAL SPECTROSCOPY OF MOLECULAR IONS IN A SUPERSONIC FREE JET

Abstract

We have recently succeeded in observing the rotational transitions of molecular ions in a supersonic free jet. The spectra have been measured by a Fourier-transform microwave spectrometer combined with a pulsed discharge nozzle (PDN), which has been proved to be powerful for studies of highly reactive neutral species, such as free radicals and carbens. So far, two protonated molecular ions, $HOCO^{+}$ and $HOCS^{+}$, have been examined, according to the previous studies in the millimeter-$wave^{1}$ and the $infrared^{2}$ regions. They were produced by pulsed discharges of a trace amount of $CO_{2}$ or OCS diluted in a $H_{2}:Ar - 1:1$ mixture. Molar fractions more than $10^{-4}$ have been achieved for those ions relative to the parent molecules, demonstrating the effective formation of ionic species using the PDN. Effects of external electric or magnetic field will be discussed in connection with controlling spacial and velocity distributions of charged species in the supersonic free jet.