Ion imaging study of reaction dynamics in the N ~+ + CH _4 system

摘要

The velocity map ion imaging method is applied to the ion-molecule reactions of N with CH _4. The velocity space images are collected at collision energies of 0.5 and 1.8 eV, providing both product kinetic energy and angular distributions for the reaction products CH _4, CH _3, and HCNH. The charge transfer process is energy resonant and occurs by long-range electron transfer that results in minimal deflection of the products. The formation of the most abundant product, CH _3, proceeds by dissociative charge transfer rather than hydride transfer, as reported in earlier publications. The formation of HCNH by C-N bond formation appears to proceed by two different routes. The triplet state intermediates CH _3NH and CH _2NH _2 that are formed as N(~3P) approaches CH _4 may undergo sequential loss of two hydrogen atoms to form ground state HCNH products on a spin-allowed pathway. However, the kinetic energy distributions for formation of HCNH extend past the thermochemical limit to form HCNH 2H, implying that HCNH may also be formed in concert with molecular hydrogen, and requiring that intersystem crossing to the singlet manifold must occur in a significant (～25) fraction of reactive collisions. We also report GAUSSIAN G2 calculations of the energies and structures of important singlet and triplet CNH _4 complexes that serve as precursors to product formation.