Λ-doublet populations in CH(A2Δ) produced in the 193 nm multiphoton dissociation of (CH3)2CO, (CD3)2CO, (CH3)2S and CH3NO2

Unequal intensities of the Λ-doublet components were observed in the CH(A²Δ-X²Π) emission following the multiphoton dissociation of (CH₃)₂CO, (CH₃)₂S and CH₃NO₂ by an ArF laser (193 nm). The power dependence of the emission intensity was estimated to be cubic (3.1±0.2) when the laser power was below ≈ 8×10¹⁷ photons cm^?2 pulse^?1. The Λ-doublet populations depended on the rotational quantum number N′ and the preferred level changed at N′ = 20. A similar behavior was observed for the CD(A²Δ) from (CD₃)₂CO. Rotational distributions show bimodal behavior, having a hump around N′ = 13 in CH(A²Δ) and N′ = 11 in CD(A²Δ). These trends indicate that the CH(A²Δ) is produced through multiple processes where stepwise mechanisms are operative via either CH₂ or CH₃, or both radicals as intermediates.