MOLECULAR-BEAM STUDY OF THE NE-ASTERISK(3S3P2,0)+O2(X3-SIGMA-G(-) REACTION - ABSOLUTE QUENCHING AND O-ASTERISK(3P5P,3P3P) PRODUCT CROSS-SECTIONS

Emission lines from O*(3p5P) and O*(3p3P) products of the reaction of Ne*(P-3(2,0)) and O2 are observed in a beam-scattering gas apparatus. The quenching cross section sigma(Q), as measured by the self-monitor method, is 31 +/- 2 A2 for average collision energies of 54 and 140 meV. The product cross sections sigma* for O*(5P) and O*(3P) are 1.8 and 1.6 angstrom2, respectively. If cross sections are assumed to reflect predominantly the P-3(2) component of the metastable beam, then the results obtained are in good agreement with beam experiments in which ion products and electron spectra are measured. To resolve an apparent inconsistency between our cross section and the most precisely measured rate constant value in the literature, we propose that the quenching cross section rises quickly from a threshold energy of approximately 16 meV to a nearly constant value at collision energies between 54 and 140 meV. The rate constant derived from this energy-dependent cross section is in excellent agreement with values measured in stationary afterglow experiments. Differences between ionization branching fractions measured directly in a flowing afterglow experiment and those determined from afterglow rate constants and crossed-beam ionization cross sections are also resolved.