Utilizing different ratios of para to ortho H(2) in normal and para enriched hydrogen, we varied the population of para-H(3)(+) in an H(3)(+) dominated plasma at 77 K. Absorption spectroscopy was used to measure the densities of the two lowest rotational states of H(3)(+).
Monitoring plasma decays at different populations of para-H(3)(+) allowed us to determine the rate coefficients for binary recombination of para-H(3)(+) and ortho-H(3)(+) ions: (p)alpha(bin)(77K) = (1.9 +/- 0.4) x 10(-7) cm(3) s(-1) and (o)alpha(bin)(77K) = (0.2 +/- 0.2) x 10(-7) cm(3) s(-1).