The collisional quenching of CCl2(A 1B1 and a 3B1) by substituted methane molecules Original Research Article

CCl2 free radical was produced by a pulsed dc discharge of CCl4 (in Ar). Ground electronic state CCl2(X) radical was electronically excited to A 1B1(0,4,0) vibronic state with Nd:YAG laser pumped dye laser at 541.52 nm. Experimental quenching data of excited CCl2(A 1B1 and a 3B1) by CH4, CH3NO2, CH3OH, and halomethanes were obtained by observing time-resolved total fluorescence signal of the excited CCl2 radical in a cell, which shows a superposition of two exponential decay components under the presence of a quencher. The quenching rate constants KA of CCl2 (A) state and Ka of CCl2 (a) state were derived by analyzing the experimental data according to a proposed three-level model to deal with the CCl2(X 1A1, A 1B1, a 3B1) system. KA and Ka increase on the whole with increasing the number of C–Cl bonds in chloromethane molecules. The formation cross sections of complexes between CCl2(A 1B1) radicals and CH4, CH3Cl, CH3OH and CH3NO2 molecules were calculated by means of a collision complex model.