Collisional quenching of electronically excited carbon atoms, C[2p2(1S0)]

Abstract

Electronically excited carbon atoms in the 2p²(¹S₀) state, 2.684 eV above the 2p²(³P₀) ground state, have been monitored in the time-resolved mode by resonance line absorption at λ= 247.9 nm [3s(¹P⁰₁)â†� 2p²(¹S₀)] following the irradiation of CCl₄ in the gas phase. The experimental arrangement, including low-energy repetitive pulsing on a flow system kinetically equivalent to a static system, pre-trigger photomultiplier gating, signal averaging and computerised analysis of the photoelectric decay signals, has been employed to study the removal of this optically metastable species by a range of added gases. Absolute rate data for the collisional quenching of C(2¹S₀) are reported for the species He, Xe, N₂, Cl₂, CO, CO₂, H₂O, CH₄, CCl₄, C₂H₂ and C₃H₆. The resulting second-order rate constants obtained by this technique are compared with those reported hitherto, principally from “single-shot” mode high-energy photolysis pulse experiments. Rate data for all the atomic states of carbon in the 2p² configuration (³P_J, ¹D₂, ¹S₀) are discussed, where appropriate, within the context of the symmetry of the potential surfaces involved in collision on the basis of the weak spin–orbit coupling approximation. The rate data for C[2p²(¹S₀)] are also compared with the analogous data for Si[3p²(¹S₀)].