New observations on the B state of the CH radical from UV multiphoton dissociation of ketene

In multiphoton dissociation experiments on ketene (CH2CO) using a UV dye laser emission spectra were observed in the 360–370 nm range. The spectra were seen only with a focused laser beam and consist of lines attributable to emission from rotational levels in the ν′ = 1 vibrational state of the B2Σ− electronic state of the methylidyne (CH) radical. In these spectra rotational transitions to the N′ = 7 level of the B state from the ground (X) state, ν″ = 0, were observed. Time-resolved fluorescence measurements on the N′ = 1, 2, 3, 4, 5 and 6 levels yielded lifetime data contributing to the existing values in the literature. Based on line broadening a lifetime estimate is given for the strongly predissociated N′ = 7 level.