Kinetics of excited-state titanium(a5F) depletion by nitric oxide, oxygen, nitrous oxide, and nitrogen

Abstract

The kinetics of depletion of ground-state Ti(a3F) and excited-state Ti(a5F) upon interactions with NO, 02, NzO, and N2 are studied in a fast-flow reactor at a He pressure of 0.70 Torr. The technique is analogous to one introduced previously (J. Phys. Chem. 1989, 93, 1576) to study reaction of Ti(a3F) with NO, 02, and N2O and uses a direct current discharge source to product Ti atoms and laser-induced fluorescence detection. Our results confirm that Ti(a3F) depletion by NO, 02, and NzO is inefficient and give 300 K effective bimolecular rate constants of (7.3 f 0.8) X (1.6 f 0.2) X 10-12, and (0.7 f 0.2) X 10-12 cm3 s-l, respectively, in agreement with previous work. In contrast to the Ti(a3F) system, depletion of excited-state Ti(a5F) upon interaction with NO, 02, and NzO is very efficient, and our measured effective bimolecular rate constants are (146 f 17) X 10-12, (135 f 29) X 10-12, and 2190 X 10-12 cm3 s-l, respectively. We also report the effective bimolecular rate constant for quenching of Ti(aSF) by NZ at 300 K to be (6.5 f 2.2) X 10-l2 cm3 s-l. Reactive differences of Ti(a3F) and Ti(aSF) with these gases are discussed, and the implications of the present results on previously proposed mechanisms for oxidation of Ti by NO, 02, and N2O are considered.