High-resolution infrared and theoretical study of gaseous oxazole in the 600-1400 cm−1 region

The Fourier transform gas-phase IR spectrum of oxazole, C3H3NO, has been recorded with a resolution of ca. 0.0030 cm−1 in the wavenumber region 600-1400 cm−1. The rotational structures of 10 fundamental bands (four of a-type, three of b-type and three of c-type) have been analysed using the Watson model. Ground state rotational and quartic centrifugal distortion constants as well as upper state spectroscopic constants have been obtained from the fits. A number of perturbations have been identified in the bands. From a local crossing observed in ν15 we located the very weak ν14 band at 858.19(1) cm−1. Also ν13 is definitively located at 899.3 cm−1. The three global c-Coriolis interacting dyads ν9/ν10, ν10/ν11, and ν12/ν13 have each been analysed by a model including first and second order Coriolis resonance using ab initio predicted first order Coriolis coupling constants; second order Coriolis interaction parameters are determined. The rotational constants, harmonic and anharmonic frequencies, intensities, and vibration-rotation constants (alphas, ανA,B,C) have been predicted by quantum chemical calculations using a cc-pVTZ basis at the MP2 and B3LYP methodology levels, and compared with the present experimental data. Both the rotational constants and frequencies are marginally closer to experiment from the B3LYP calculations. In order to make more significant comparisons between theory and experiment for the alphas, we take differences between ground and vibronic state values; under these circumstances, the B3LYP definitely have a closer fit to experiment.