The high-resolution infrared spectrum of thiophene between 600 and 1200 cm−1: A spectroscopic and theoretical study of the fundamental bands ν6, ν7, ν13, and the c-Coriolis interacting dyad ν5, ν19

The Fourier transform infrared spectrum of gaseous thiophene, C4H4S, has been recorded in the 600-1200 cm−1 spectral region with a resolution of ca. 0.0030 cm−1. Five fundamental bands ν13 (B1, 712.1 cm−1), ν7 (A1; 840.0 cm−1), ν6 (A1; 1036.4 cm−1), ν5 (A1; 1081.5 cm−1) and ν19 (B2; 1084.0 cm−1) have been analysed by the standard Watson model (A-reduction). Ground state rotational and quartic centrifugal distortion constants have been obtained from a simultaneous fit of ground state combination differences from four of these bands and previous microwave transitions. Upper state spectroscopic constants have been obtained for all five bands from single band fits using the Watson model. A strong c-Coriolis resonance perturbs the close lying ν5 and ν19 bands. We have analysed this dyad system by a model including first and second order Coriolis resonance using the theoretically predicted Coriolis coupling constant ς19,5c. From this analysis we locate the previously unobserved ν19 band at 1083.969 cm−1. The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational constants (α-constants) predicted by quantum chemical calculations using a cc-pVTZ basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and α-constants for all fundamental levels of the molecule is given.