Investigation of collisional quenching of CCl2( 1B1 and ã 3B1) by some inorganic molecules

CCl2 free radicals were produced by a pulsed dc discharge of CCl4 in Ar. The radicals were electronically excited from the ground electronic state to the Ã 1B1 (0,4,0) state with Nd:YAG laser pumped dye laser at 541.52 nm in the rR subband. Experimental quenching data of CCl2(Ã 1B1) and CCl2(ã 3B1) by O2, N2, NO, NH3, H2O, CO2, CS2, SO2, and SF6 molecules were monitored by observing the time-resolved total fluorescence signals of the excited CCl2 in a cell where the total pressure was 200 Pa. The observed profiles showed a superposition of two exponential decay components in the presence of the quencher. The quenching rate constants kA of CCl2(Ã) and ka of CCl2(ã) were derived by analyzing the experimental data according to a proposed three-level-model to deal with the CCl2( 1A1, Ã 1B1, ã 3B1) system. The order of magnitude for the rate constant of the quenching of the à state (kA) is 10−10 cm3 s−1, while for the quenching rate constant of the ã state (ka) is 30–50% of kA. By changing the excitation wavelength, the radicals of the ground electronic state CCl2() were electronically excited to a different vibronic state, i.e. (0,3,0), (0,4,0), (1,3,0), (0,6,0), (1,4,0) and (2,2,0), of CCl2(Ã 1B1). We studied the kinetics of the collisional quenching by H2O and NH3 molecules of CCl2(Ã 1B1) in different vibronic states. It is found that the total quenching rate constant kA is little dependent on the vibronic state. It is possible that the reaction between the quencher molecule and CCl2(Ã 1B1) undergoes a process without a barrier. An explanation for the measured quenching data using the complex model based on attractive forces between the collision partners is presented.