Kinetics of Excited - State Ti ( a 5 F ) Depletion by NO , 02 , N 20 , and N 2

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, 0 2 , 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, 0 2 , 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, 0 2 , 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, 0 2 , and N2O are considered.