Nuclear spin state-resolved cavity ring-down spectroscopy diagnostics of a low-temperature -dominated plasma

Abstract

We have applied a continuous-wave near-infrared cavity ring-down spectroscopy method to study the parameters of a -dominated plasma at temperatures in the range 77–200 K. We monitor populations of three rotational states of the ground vibrational state corresponding to para and ortho nuclear spin states in the discharge and the afterglow plasma in time and conclude that abundances of para and ortho states and rotational temperatures are well defined and stable. The non-trivial dependence of a relative population of para- on a relative population of para-H2 in a source H2 gas is described. The results described in this paper are valuable for studies of state-selective dissociative recombination of ions with electrons in the afterglow plasma and for the design of sources of ions in a specific nuclear spin state.