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

Abstract

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 k_A of CCl₂(Ã) and k_a 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 (k_A) is 10⁻¹⁰ cm³ s⁻¹, while for the quenching rate constant of the ã state (k_a) is 30–50% of k_A. 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 k_A 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.