Time-resolved kinetic studies on quenching of C₂ (d ³Π_g) by alkanes and substituted methane molecules

C₂ free radicals were produced by photolysis of selected precursors (C₂Cl₄) with the focused output from the fourth harmonic of a Nd: YAG laser at 266 nm. The generated C₂ (a ³Π_u) radicals were then electronically excited to the d³Π_g state with a Nd: YAG laser pumped dye laser at 516.5 nm in the (0,0) band of the C₂ (d³Π_g ← a³Π_u) transition. The rate constants k _q and averaged collision cross sections σ_q for collision quenching of C₂ (d³Π_g) by n-C _nH_2n+2 (n = 1-8) and CH_4-nCl_n (n = 2-4) were measured at room temperature (298 K) by time-resolved laser-induced fluorescence in cell at total pressure of about 15 Torr. Formation cross sections of complexes for the C₂ (d³Π_g) and quenchers were calculated by means of a collision complex model. It was shown that the quenching rates of C₂ (d³Π_g) by alkane molecules increase with the number of C-H bonds of the molecules, which is in agree with that of the measured quenching cross sections.