Knowledge Bank

A free jet has been used to form van der Waals complexes of the s-tetrazine (Ar)n(He)m with n ranging from zero to three and m from zero to six. The electronic ratational spectra indicate these are near prolate top molecules with type A contours. The spectra have been used along with the band shift rule to assign the structure and composition of these complexes. The complex tetrazine-Ar has the argon centered above the ring at a distance of 3.45 {\AA} in the ground electronic state and 3.45 {\AA} in the excited electronic state. This decrease in bond length upon electronic excitation is consistent with the observed red shift of $-23cm-1$ from the s-tetrazine electronic origin. Tetrazine-$Ar2$ has the argons centered above and below the ring and has a similar bond length change from 3.44 {\AA} to 3.40 {\AA} between ground and excited states. The spectral shift is $-46cm-1$. By seeding s-tetrazine into a mixture of argon and helium gases mixed complexes were observed. More than two noble gas atoms add to the ring only when argon is already present on the ring. While the first two rare gas atoms bind directly to the tetrazine ring, all additional rare gas atoms bind to the argon atoms that are bound to the tetrazine ring.