The low translational energy dependence of the reaction Ar+(2P3/2,1/2)+H2(D2)

We report the measurement of the spin–orbit state specific rate coefficients for the reactions Ar+(2P3/2,1/2)+H2(D2) at translational temperatures from 0.5 to 3 K in a free jet flow reactor. The measured rate coefficient for Ar+(2P3/2) with either H2 or D2 shows a slow monotonic increase with increasing collision energy from 4×10−5 to 10 eV. The observed kinetic isotope effect at low energy is consistent with the simple mass-dependent change in the collision frequency. Below 3 K, excitation into the 2P1/2 state is found to enhance the total reaction rate by a factor of 2.7 for the reaction with H2 and by 1.6 for the reaction with D2. The full range of energy-dependent experimental results are compared to current reaction models.