The spectroscopy of dimethyl-s-tetrazine cooled in a supersonic free jet

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Abstract
The fluorescence excitation and dispersed emission spectra of dimethyl tetrazine have been observed in a supersonic free jet. Measurements of vibrational structure in the low resolution fluorescence excitation spectrum and in the single vibronic level emission spectrum have allowed us to confirm and extend vibrational assignments made in the static gas and solid matrix. The spectrum is dominated by progressions in the mode ν6a with strong progressions in ν1 as well. Excited vibrational levels of ν6a in the upper electronic state appear to be perturbed. The progression in ν1 is considerably more intense in dimethyl tetrazine than it is in tetrazine. The vibrational modes ν2, ν8a, ν16a, and ν16b have been assigned. Of these, the assignments of the first three agree with previous work, while the assignment of ν16b is at a much lower frequency. Rotational structure has been resolved at the origin band, and torsionless m=0 transitions have been assigned. Analysis of the m=0 levels indicates that the ring bond lengths and internal angles and their changes upon electronic excitation are similar to those of s-tetrazine and methyl-s-tetrazine.