Abstract
Ab initio harmonic force fields were calculated for 1,3,4-oxadiazole and 1,3,4-thiadiazole at the Møller-Plesset (MP2) level of theory using the 6–31G
∗∗ basis set at the corresponding optimized geometries assuming a
C
2
v
symmetry. Scaled quantum mechanical (SQM) force fields for both molecules were calculated using the experimental vibrational frequencies available from the literature. Under the
C
2
v
symmetry constraint, the assignment of the experimental to the calculated frequencies for both molecules and their -2,5-
d
2 and -2-
d
1 (
C
s
symmetry) isotopomers was performed. Vibrational absorption intensities were calculated using the MP2 dipole derivative tensors. The calculations showed possible misassignment for 1,3,4-oxadiazole and its -2,5-
d
2 and -2-
d
1 isotopomers and indicated misassignments for 1,3,4-thiadizole and its -2,5-
d and -2-
d
1 isotopomers. Good agreement between the experimental and calculated frequencies and absorption intensities was found.