LABORATORY SYNTHESIS OF MOLECULAR-HYDROGEN ON SURFACES OF ASTROPHYSICAL INTEREST

We report on the first results of experiments to measure the recombina tion rate of hydrogen on surfaces of astrophysical interest. Our measu rements give lower values for the recombination efficiency (sticking p robability S times the probability of recombination upon H-H encounter , gamma) than model-based estimates. We propose that our results can b e reconciled with average estimates of the recombination rate [(1/2)n( H)n(g)v(H)AS gamma] from astronomical observations, if the actual surf ace of an average grain is rougher, and its area bigger, than the one considered in models.