DYNAMICS OF THE C2H2- A VIBRATIONAL-MODE-SELECTIVE SCATTERING STUDY(+ND3 REACTION )

The C2H2+ + ND3 reaction has been studied using mode-selective prepara tion of the C2H2+ reactant in conjunction with measurements of the pro duct ion recoil velocity distributions. The only product channels obse rved over a collision energy range from 0.1 to 5 eV (CM) are ND3+, ND3 H+, and ND2H+ No evidence for the formation of covalently bound interm ediates is found, despite the existence of several strongly bound isom ers of C2H5N+. Also not observed is H atom abstraction. The absence of these channels is surprising in light of their importance in the ener getically similar C2H2+ + CH4 system. The ND3+ charge-transfer reactio n is found to proceed at low collision energies via a weakly bound [C2 H2:ND3](+) intermediate with lifetime around 1 ps. At high energies, c harge transfer occurs mostly by long-range electron hopping. Proton tr ansfer is direct at all energies, though the time scale of the collisi ons approaches 300 fs at low energies. Vibrational effects are mode-sp ecific and change with collision energy and product channel. A collisi on energy and vibrational-mode-dependent reaction mechanism is propose d.