Vibrational frequencies in the à 3E state of methylnitrene

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Abstract
New observations have enabled the identification of another excited state vibration in the à 3E –X̃ 3A2 ultraviolet absorption spectrum of matrix‐isolated methylnitrene. Two progressions in the C–N stretching frequency ν3 were detected in both CH3N and CD3N, with average intervals of 710 and 695 cm−1, respectively. For each isotopomer, corresponding lines in the pair of progressions are offset by frequencies appropriate for a methyl vibration. This provides the first clear evidence for excitation of the CH3 symmetric deformation (umbrella mode) ν2 in the upper state of the transition, with vibrational frequencies of 1166 cm−1 for CH3N and 1044 cm−1 for CD3N. These observations confirm earlier speculation on the absorption spectrum of matrix‐isolated CH3N, and correlate with unidentified lines in the gas phase emission spectrum. The use of a new precursor, methyl isocyanate, in the generation of this radical is also of interest.