Fluorescence excitation spectrum of s-tetrazine cooled in a supersonic free jet: Van der waals complexes and isotopic species

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Abstract
Van der Waals complexes between s‐tetrazine and a number of light gases have been observed and characterized by laser spectroscopic studies of a free supersonic expansion of s‐tetrazine in a helium carrier gas. The observed complexes are of the form X–s‐tetrazine and X2–s‐tetrazine where X=He, H2, and Ar. The spectra are consistent with the X species in both types of complexes being bound on or near the out‐of‐plane C 2v axis on the top and/or bottom of the s‐tetrazine ring. For the He and H2 complexes, analysis of the rotational structure indicates that the van der waals bond length is ∼3.3 Å. The observed red shift of the O–O band of the 1 B 3u ←1 A 1g transition of all complexes relative to that of s‐tetrazine indicates that a slighly stronger van der waals bond exists in the excited state. Observed vibrational progressions for these complexes indicates the stretching frequency of the van der waals bond in the excited state is 38.0, 95, and 110 cm−1 for the X=He, H2 and Ar complexes, respectively. The O–O band origins of the 12C2 14N4HD, 12C2 14N4D2, 12C13C14N2H2, and 12C2 14N3 15NH2 isotopic species relative to that of 12C2 14N2H2 are also reported.