Dissociative recombination coefficients for H3(+), HCO(+), N2H(+), and CH5(+) at low temperature - Interstellar implications

The results obtained from a recent laboratory study of the dissociative recombination coefficients, alpha, at 95 and 300 K for the important interstellar ions H3(+), HCO(+), N2H(+) and CH5(+). The most important result of the study is that alpha-H3(+) is much smaller than previous studies had indicated, so small that it was only possible to obtain an upper limit value at both temperatures. However, the values of alpha-HCO(+), alpha-N2H(+) and alpha-CH5(+) have been determined at both temperatures, and they are in accordance with expectations based on previous laboratory data. The smaller alpha-H3(+) implies a larger fractional ionization of dense interstellar clouds than previous estimates had indicated. Some possible consequences of a higher ionization density to the physics and chemistry of dense clouds are mentioned.