Nuclear spin effect on recombination of H₃⁺ ions with electrons at 77 K

Utilizing different ratios of para to ortho H₂ in normal and para enriched hydrogen, we varied the population of para-H₃⁺ in an H₃⁺ dominated plasma at 77 K. Absorption spectroscopy was used to measure the densities of the two lowest rotational states of H₃⁺. Monitoring plasma decays at different populations of para-H₃⁺ allowed us to determine the rate coefficients for binary recombination of para-H₃⁺ and ortho-H₃⁺ ions: (p)α(bin)(77 K) = (1.9 ± 0.4) × 10⁻⁷ cm³ s⁻¹ and (o)α(bin)(77 K) = (0.2 ± 0.2) × 10⁻⁷ cm³ s⁻¹.