Estimates of N2 abundances in dense molecular clouds

Interstellar abundances toward 13 dark clouds and warm star-forming regions are derived from column densities measured for N2H+, under the assumption that the quiescent gas in the clouds has achieved a steady state chemistry. The N2 abundances were found to be about 4 x 10 exp -6 with a small dispersion about the mean. No significant differences were found between the amount of N2 in dark and in warm clouds, which suggests that interstellar grains may not play an important role in the N2 production or depletion in dense gas. The relatively high abundances found suggest that N2 is probably the dominant nitrogen-bearing species in dense clouds.