OH Alpha 2Sigma(+) Yields Chi 2Pi Chemiluminescence Measurements of Nsub2(+), Ar(+) + Hsub2O Hydrogen-Atom-Transfer Reactions at Suprathermal Energies
PHILLIPS LAB HANSCOM AFB MA
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Chemiluminescence attributable to OH Alpha 2Sigma yields Chi 2Pi emission is observed in hydrogen-atom transfer reactions of Nsub2 and Ar with Hsub2O. High-resolution OH Alpha yields Chi spectra 0.5 nm full width at half maximum FWHM are presented as a function of collision energy in the range Esubc.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 Alpha state is formed via two channels. In the dominant channel, Alpha state OH is formed in both v0 and v1, with a collision energy-dependent rotational temperature ranging from 1000 K at Esubc.m. 6 eV to 3400 K at Esub c.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 Alpha state OH primarily in the v0 vibrational level with a rotational temperature of 300 K. Comparison of low-resolution 4 nm FWHM OH Alpha yields Chi and Hsub2O alpha2 Alphasub1 yields Chi2 Betasub1 emissions provides an estimate for the OH Alpha state cross sections of sigma 0.3 x 10 to the minus 16th cm sq for Nsub2 Hsub2O at Esubc.m. between 6 and 20 eV, representing less than 10 of the hydrogen atom pickup channel at these energies. For Ar Hsub2O at Esubc. m. between 11 and 32 eV, the estimated OH Alpha state cross section is sigma 0.5 A2, which may represent all of the hydrogen atom pickup channel at the higher energies.
- Radiation and Nuclear Chemistry
- Atomic and Molecular Physics and Spectroscopy
- Particle Accelerators