Dynamics of the C2H2++ND3 reaction: A vibrational-mode-selective scattering study

The C2H2+ + ND3 reaction has been studied using mode-selective preparation of the C2H2+ reactant in conjunction with measurements of the product ion recoil velocity distributions. The only product channels observed over a collision energy range from 0.1 to 5 eV (CM) are ND3+, ND3H+, and ND2H+ No evidence for the formation of covalently bound intermediates is found, despite the existence of several strongly bound isomers of C2H5N+. Also not observed is H atom abstraction. The absence of these channels is surprising in light of their importance in the energetically similar C2H2+ + CH4 system. The ND3+ charge-transfer reaction is found to proceed at low collision energies via a weakly bound [C2H2:ND3](+) intermediate with lifetime around 1 ps. At high energies, charge transfer occurs mostly by long-range electron hopping. Proton transfer is direct at all energies, though the time scale of the collisions approaches 300 fs at low energies. Vibrational effects are mode-specific and change with collision energy and product channel. A collision energy and vibrational-mode-dependent reaction mechanism is proposed.