Vibronic analysis of the A→X laser-induced fluorescence of jet-cooled methoxy (CH3O) radical

The dispersed fluorescence of the à 2A1–X̃ 2E system of CH3O and 13CH3O in a supersonic jet was recorded after excitation of various vibrational levels of the à state. Analysis of the spectra yielded ν2″ = 1412, ν3″ = 1047, ν5″ = 1494, and ν6″ = 653 cm−1 for the X̃ state of 12CH3O, and ν2″ = 1408, ν3″ = 1027, ν5″ = 1488, and ν6″ = 649 cm−1 for 13CH3O. The least-squares fitting of the observed 300–306 lines (with spin–orbit splitting removed) yielded ωe=1057±3 cm−1 and ωexe=7.0±0.7 cm−1 for ν3″ of 12CH3O. Several tentative assignments were also made on the basis of the improved fluorescence spectra. The Fermi-resonant levels 1289 and 1319 cm−1 above v=0 of the à state were also reassigned; the former is better represented as v2′ = 1, whereas the latter is represented as v3′ = 2.