s-Tetrazine. II. Infrared Spectra

Abstract

To aid in the vibronic analysis of the n→π^* visible absorption band systems of s‐tetrazine vapor, infrared spectra of vapor, solution, and cold, solid film phases of natural and deuterated mixtures of s‐tetrazine have been obtained. By use of the product rule and by correlation of the fundamental modes of s‐tetrazine with those of benzene and the other azines, it is possible to make tentative vibrational assignments for all seven of the fundamental bands that would be expected to be infrared active in the wavelength region from 2 to 15 μ. However, the low‐frequency modes 16a and 16b, A_u and B_1u, respectively, have not yet been observed, and the lack of knowledge of the frequencies of eight of the nine gerade modes (Raman active only) has prevented any definite assignment of combination bands. The observation of an interesting and peculiar phenomenon—what is believed to be the totally symmetrical mode 6a near 730 cm^—1 in the solid film spectra of the various deuterated mixtures—is also reported.