High-resolution infrared and theoretical study of four fundamental bands of gaseous 1,3,4-oxadiazole between 800 and 1600 cm-1

The Fourier transform infrared spectrum of gaseous 1,3,4-oxadiazole, C2H2N2O, has been recorded in the 800-1600 cm(-1) wavenumber region with a resolution around 0.0030 cm(-1). The four fundamental bands v(9)(B-1; 852.5 cm(-1)), V]4(B-2; 1078.5 cm(-1)), v(4)(A(1); 1092.6 cm(-1)), and v(2)(A(1); 1534.9 cm(-1)) are analyzed by the standard Watson model. Ground state rotational and quartic centrifugal distortion constants are obtained from a simultaneous fit of ground state combination differences from three of these bands and previous microwave transitions. Upper state spectroscopic constants are obtained for all four bands from single band fits using the Watson model. The v(4) and v(14) bands form a c-Coriolis interacting dyad, and the two bands are analyzed simultaneously by a model including first and second order Coriolis resonance using the ab initio predicted Coriolis coupling constant zeta(c)(14,4) . An extended local resonance in v(2) is explained as higher order b-Coriolis type resonance with v(6) + v(10), which is further perturbed globally by the v(15) + v(10) level. A fit of selected low-J transitions to a triad model including v(2)(A(1)), v(6) + v(10)(B-1), and v(15) + v(10)(A(2)) using an ab initio calculated Coriolis coupling constant zeta(c)(15,6) is performed. The rotational constants, ground state quartic centrifugal distortion constants, anharmonic frequencies, and vibration-rotational constants (alpha-constants) predicted by quantum chemical calculations using a cc-pVTZ and TZ2P basis with B3LYP methodology, are compared with the present experimental data, where there is generally good agreement. A complete set of anharmonic frequencies and alpha-constants for all fundamental levels of the molecule is given. (c) 2007 Elsevier Inc. All rights reserved.