KINETICS OF EXCITED-STATE TI(A5F) DEPLETION BY NO, O2, N2O, AND N2

The kinetics of depletion of ground-state Ti(a3F) and excited-state Ti (a5F) upon interactions with NO, O2, N2O, and N2 are studied in a fast -flow reactor at a He pressure of 0.70 Torr. The technique is analogou s to one introduced previously (J. Phys. Chem. 1989, 93, 1576) to stud y reaction of Ti(a3F) with NO, O2, and N2O and uses a direct current d ischarge source to product Ti atoms and laser-induced fluorescence det ection. Our results confirm that Ti(a3F) depletion by NO, O2, and N2O is inefficient and give 300 K effective bimolecular rate constants of (7.3 +/- 0.8) X 10(-12), (1.6 +/- 0.2) X 10(-12), and (0.7 +/- 0.2) x 10(-12) cm3 s-1, respectively, in agreement with previous work. In con trast to the Ti(a3F) system, depletion of excited-state Ti(a5F) upon i nteraction with NO, O2, and N2O is very efficient, and our measured ef fective bimolecular rate constants are (146 +/- 17) x 10(-12), (135 +/ - 29) x 10(-12), and greater-than-or-equal-to 190 x 10(-12) cm3 s-1, r espectively. We also report the effective bimolecular rate constant fo r quenching of Ti(a5F) by N2 at 300 K to be (6.5 +/- 2.2) x 10(-12) cm 3 s-1. Reactive differences of Ti(a3F) and Ti(a5F) with these gases ar e discussed, and the implications of the present results on previously proposed mechanisms for oxidation of Ti by NO, O2, and N2O are consid ered.