CH(A, B–X ) fluorescence from vacuum ultraviolet excitation of CH3

CH3 was produced by the reaction of Cl or F with CH4 in a flow tube. The CH(A 2Δ, B 2Σ−–X 2Πr) fluorescence was observed from photoexcitation of CH3 at 157 nm by a single-photon excitation process and at 193 nm by two-photon excitation. No emission was detected at 248 nm. The fluorescence cross section at 157.5 nm was estimated to be about 8×10−19 cm2 with an uncertainty of factor 3. The CH2 emission is negligibly weak. The photodissociation process for the absorption continua of CH3 is discussed.