Rate Coefficients for D(1s) + H^+ <--> D^+ + H(1s) Charge Transfer and Some Astrophysical Implications

Abstract

We have calculated the rate coefficients for D(1s) + H^+ <--> D^+ + H(1s) using recently published theoretical cross sections. We present results for temperatures T from 1 K to 2x10^5 K and provide fits to our data for use in plasma modeling. Our calculations are in good agreement with previously published rate coefficients for 25 <= T <= 300 K, which covers most of the limited range for which those results were given. Our new rate coefficients for T >~ 100 K are significantly larger than the values most commonly used for modeling the chemistry of the early universe and of molecular clouds. This may have important implications for the predicted HD abundance in these environments. Using our results, we have modeled the ionization balance in high redshift QSO absorbers. We find that the new rate coefficients decrease the inferred D/H ratio by <~ 0.4%. This is a factor of >~ 25 smaller than the current >~ 10% uncertainties in QSO absorber D/H measurements.