The Complete Substitution Structure of 1,2,5-Thiadiazole

Abstract

Abstract Double Resonance M odulation (DRM) microwave spectroscopy has been used to determine the complete substitution structures of 1,2,5-thiadiazole and 3,4-d2-1,2,5-thiadiazole. The 34S-, 13C- and 15N-species o f these two “parent” molecules were studied in natural abundance. The structure parameters o f the two parent forms agree to within ± 0.0005 Å and ± 0.02° with the following averaged values: Distances (in Å) S - N = 1.6296 C = N = 1.3270 C - C = 1.4167 C - H = 1.0805 Angles (in degrees) NSN = 99.44 SNC = 106.51 NCC = 113.77 CCH = 126.27 The new data confirm the earlier work on this substance, but the precision o f the structure parameters is improved by a factor of ~ 10. The apparent C-C bond length in the normal species is found to differ by ~ 0.001 A from that in the 3,4-d2-species. Vibrational contributions (⊿Ivib) to the effective changes of the moments o f inertia are determined for the sulphur atom and the near-axis nitrogen atoms as ⊿Ivib(S) = - 0.0017 μÅ2 and ⊿Ivib(N) = - 0.0035 μÅ2. Energy transfer through collisions has been exploited to overcome traditional difficulties in the identification o f high-J Q-branch transitions o f rare isotopic forms.