Knowledge Bank

S-tetrazine cooled in a supersonic free jet expansion has been found to form dimers with two distinct conformations. High resolution laser induced fluorescence of both hydrogen and deuterium substituted dimers has yielded excitation spectra whose structure is lifetime-width limited. Dimer structures were determined by a combined rotational contour generating program and nonlinear least squares program. One dimer to planar with two translationally equivalent conoder units. A hydrogen of each ring is in close proximity with the nitrogen lone pair of the other allowing for stabilization by weak hydrogen bonds. The center to center ring separation is $5.6\backslash AA$. The other dimer is T-shaped with symmetrically inequivalent rings giving rise to two electronic transitions with different rotational structure. The ring centers are separated by $4.4\backslash AA$. Each dimer forms a vibrational progression of $703cm-1$ which correlates to the known 6a tetrazine monome progression. Low frequency vibrations observed in both fluorescence excitation and dispersed fluorescence are attributed to some of the six new normal vibrations which result upon dimer formation.