Kinetic studies on the collisional quenching of CCl2((A)over-tilde(1)B(1) and (a)over-tilde(3)B(1)) by ketones

CCl2 free radicals were produced by a pulsed dc discharge of CCl4 (in Ar). The ground electronic state CCl2 (X) radical was electronically excited to the (A) over tilde B-1(1) (040) vibronic state with a Nd:YAG laser pumped d ye laser at 541.52 run. Experimental quenching data of excited CCl2 ((A) ov er tilde B-1(1) and (a) over tilde B-3(1)) by ketone molecules were obtaine d by observing time-resolved total fluorescence signal of the excited CCl2 radical, which showed a superposition of two exponential decay components u nder the presence of quencher. The quenching rate constants K-A of CCl2 (A) state and K-a of CCl2 (a) state were derived by analyzing the experimental data according to a proposed three-level-model involving (X) over tilde (1 )A(1), (A) over tilde B-1(1), and (a) over tilde B-3(1) states. On the whol e, K-A and K-a increase with increasing the number of C-H bonds in ketone m olecules. (C) 2001 Elsevier Science B.V. All rights reserved.