Ion imaging study of reaction dynamics in the N+ + CH4 system

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(3)NH(+) and CH(2)NH(2)(+) that are formed as N(+)((3)P) 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.