OH A  2∑+→ X  2Π chemiluminescence measurements of N+2, Ar++H2O hydrogen-atom-transfer reactions at suprathermal energies

Chemiluminescence attributable to OH A 2∑+→X 2Π emission is observed in hydrogen-atom transfer reactions of N+2 and Ar+ with H2O. High-resolution OH A→X spectra [0.5 nm full width at half maximum (FWHM)] are presented as a function of collision energy in the range Ec.m.=5–20 eV. The spectra clearly show an increase in rotational broadening with collision energy. To reasonably fit the spectral data, simulations require contributions from two Boltzmann distributions with different rotational temperatures. It is proposed that the OH A state is formed via two channels. In the dominant channel, A state OH is formed in both v′=0 and v′=1, with a collision energy-dependent rotational temperature ranging from 1000 K at Ec.m.=6 eV to 3400 K at Ec.m.=19 eV. The rotationally excited products are proposed to be formed in a two-step reaction involving charge transfer, followed by the transfer of a proton to the ‘‘primary’’ species. The second channel is characterized by formation of A state OH primarily in the v′=0 vibrational level with a rotational temperature of 300 K. Comparison of low-resolution (14 nm FWHM) OH A→X and H2O+ Ã 2A1→X̃ 2B1 emissions provides an estimate for the OH A state cross sections of σ