Reaction of N+ Ion with H2, HD, and D2 at Low Temperatures: Experimental Study of the Pathway to Deuterated Nitrogen-containing Molecules in the Interstellar Medium

This work is motivated by many observations of nitrogen hydrides including their isotopologues in the interstellar space. We studied the formation of NH+ and ND+ ions in the nearly thermoneutral hydrogen abstraction reactions of N+ ions with H-2, HD, and D-2 at temperatures from 300 K down to 15 K using a variable-temperature 22-pole radio frequency ion trap. For the reaction of N+ with HD, the branching ratios for production of ND+ and NH+ ions were also determined. The activation energies of all four reaction channels were determined from the temperature dependencies of the measured reaction rate coefficients. Under the assumption of no energy barriers on the reaction paths, we derive the vibrationless energy change (i.e., the difference of equilibrium Born-Oppenheimer potential energies of products and reactants) in the reactions as Delta E (e) = (103 +/- 3) meV.