Kinetic study of electronically excited carbon atoms C(21S0)

Abstract

A kinetic study of the collisional behaviour of the electronically excited optically metastable carbon atom, C[2p²(¹S₀)], 2.684 eV above the 2p²(³P₀) ground state, is presented. C(2¹S₀) was generated by the repetitive, pulsed irradiation of CCl₄ in a flow system and monitored photoelectrically in absorption by resonance line attenuation at λ= 247.9 nm [3s(¹P⁰₁)â†� 2p²(¹S₀)]. The experimental system, incorporating pre-trigger photomultiplier gating, signal averaging and computerised analysis of the atomic decays, yields considerably improved rate data for the ¹S₀ state compared with those reported hitherto from the results of “single-shot” measurements. Collisional rate data for all the states of atomic carbon and also silicon arising from the np² configuration, namely, C(2³P_J, 2¹D₂, 2¹S₀) and Si(3³P_J, 3¹D₂, 3¹S₀), are considered in general terms within the context of symmetry arguments on the nature of the potential surfaces involved using the weak spin–orbit coupling approximation. The data for C + H₂, O₂ and C₂H₄ are discussed in some detail. Correlation diagrams connecting the states of C + H₂ and CH + H via the state manifold of CH₂, and C + O₂ and CO + O via the state manifold of CO₂ are presented. An approximate potential energy diagram for [graphics omitted] in C_2v symmetry, based on electron occupancy arguments, is also presented and employed to discuss the rate data for C(2³P_J, 2¹D₂, 2¹S₀)+ C₂H₄.