Vibrational spectroscopic studies of matrix isolated molecules
The Raman spectrum of polycrystalline or matrix-isolated S2N2 shows three bands attributable to its Raman active fundamentals, including two in close proximity; the possibility of Fermi resonance is discounted. The infrared spectrum.of polycrystalline S2N2 shows five bands, including three attributable to the infrared active fundamentals, while the others are associated with some intermediate species in the polymerisation of S2N2. The vibrational spectra of matrix-isolated S4N4 are consistent with previous observations in the solid state and in solution, also with the established cage structure of the molecule. The stretching force constants of S2N2 and S4N4, lower than those predicted on the basis of observations on acyclic S-N molecules, are correlated with the strain in the molecules and their associated thermodynamic instability. The interaction force constants indicate delocalised π-bonding, apparently more extensive in S2N2. Substantial cross-ring S-S bonding is evident in S4N4; S-S interactions in S2N2 are apparently non-bonded and repulsive in nature. The infrared spectrum of matrix-isolated Cr0C13 contains bands attributable to the fundamentals of this molecule, along with several indicating the presence of Cr02C12 and possibly other related molecules. The Raman spectrum shows just three strong bands, all below 250 cm-1, assumed to arise from the deformation fundamentals of Cr0C13; the form of the spectrum is attributed to absorption or fluorescence. The force constants derived for Cr0C13 correspond closely to their counterparts in V0C13 and Cr02C12, suggesting similar force fields in the three molecules. The infrared spectrum of the volatile products of the reaction between PC13 and NaN3 indicates the presence of several molecules, possibly including C12PN3 and oligomers of C12 P = N, although no definite conclusions are drawn. Spectroscopic evidence also suggests that the reaction between (CH3)2PC1 and NaN3 yields (CH3)2PN3 as a major product, although observations such as the effect of ultraviolet photolysis remain unexplained.