15min:
NUCLEAR SPIN DEPENDENCE OF THE REACTION OF H3+ WITH H2.

KYLE N. CRABTREE, BRIAN A. TOM, CARRIE A. KAUFFMAN, BENJAMIN J. MCCALL, Department of Chemistry, University of Illinois, Urbana, IL 61801.

The chemical reaction H3+ + H2 rightarrow H2 + H3+ is the simplest bimolecular reaction involving a polyatomic, and is possibly the most common such process occurring in the universe. Recent measurements of interstellar clouds have shown that the temperatures derived from the lowest rotational levels of H2 and H3+ do not agree, and it is expected that this reaction plays a key role in this deviation. To investigate this process, we have measured the ortho/para ratio of H3+ produced in this reaction by performing high resolution spectroscopy on its nu2 fundamental band in plasmas formed from various mixtures of ortho and para H2. These measurments have been performed in a supersonic expansion discharge source and in a cooled hollow cathode cell to probe the reaction at a variety of temperatures at and below 300 K. Our results provide experimental evidence that the population distribution of the lowest levels of H3+ is governed by the steady state of the H3+ + H2 rightarrow H2 + H3+ reaction, not by thermalization.