THE ELECTRONIC SPECTROSCOPY AND STRUCTURE OF 3-AMINO-S-TETRAZINE IN A SUPERSONIC JET

The electronic spectroscopy of 3-amino-s-tetrazine (AT) has been studied in a supersonic jet. Low-resolution vibrationally resolved fluorescence excitation and dispersed fluorescence spectra have enabled us to assign the fundamental frequencies of six vibrational normal modes in both the ground and excited states. The spectra are dominated by progressions in v6a; substantial intensity is also seen in v1. The frequency of the amino inversion vibration fundamental suggests that the barriers to amino inversion of AT in the ground and excited states may be quite different from the corresponding barriers in aniline. High-resolution rotationally resolved spectra have been obtained for the AT origin transition. The transition dipole moment is polarized along the C inertial axis, which is consistent with the excited state being the A ̃1B1(π* ← n) state. The rotational constants indicate that the internal NCN angle decreases by 3.4° upon excitation; this geometry change is along the v6a normal mode, and is consistent with the observed v6a progression. The CNH2 bond is much shorter than a typical CNH2 single bond, indicating that this bond has partial double bond character caused by amino lone pair participation in the π aromatic system. © 1990.