High-resolution infrared and theoretical study of the fundamental bands ν₆, ν₇, ν₉ and ν₁₃ of 1,2,3-thiadiazole

The Fourier transform gas-phase IR spectrum of 1,2,3-thiadiazole, C2H2N2S, has been recorded with a resolution of ca. 0.003cm(-1) in the 700-1100cm(-1) spectral region. Four fundamental bands nu(6)(A(I); 1101.8 cm(-1)), nu(7)(A(I); 1038.8 cm(-1)), nu(g)(A(I), 858.9 cm(-1)), and nu(13)(A(II); 746.2 cm(-1)) have been analyzed using the Watson model in A-reduction. Two additional bands nu(8)(A(I); 894.6 cm(-1)) and nu(12)(A(II); 881.2 cm(-1)) were assigned by their weak Q-branches. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from fits. A number of weak global and local interactions are present in the bands. The resonances identified were qualitatively explained by Coriolis type perturbations with neighboring levels. Ground state rotational and quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational a-constants predicted by quantum chemical calculations using a cc-pVTZ basis and B3LYP methodology, have been compared with the present experimental data, where there is generally good agreement. (c) 2008 Elsevier Inc. All rights reserved.