Millimeter-wave and infrared spectroscopy of thiazole (c-C3H3NS) in its ground state and lowest-energy vibrationally excited states (ν18, ν17, and ν13)

Abstract

Abstract The rotational spectrum of thiazole (c-C3H3NS, Cs, μa\xa0=\xa01.3 D, μb\xa0=\xa00.97 D) from 130 to 375\xa0GHz and high-resolution infrared spectrum from 300 to 1300\xa0cm−1 were obtained and analyzed. Nearly 4700 new, pure-rotational transitions were measured for the ground vibrational state, as well as over 1400 transitions for each of its three lowest-energy vibrationally excited states (ν18, ν17, and ν13). A total of over 5500 rotationally resolved, infrared transitions were measured for fundamentals ν17 and ν13, which form a Coriolis-coupled dyad. Transitions for each of these vibrational states of thiazole were fit to a sextic, A-reduced Hamiltonian in the Ir representation. Computed CCSD(T) values of the spectroscopic constants of thiazole show remarkable agreement with the experimentally determined values. Deuterium enrichment of thiazole allowed for the observation of the ground state and first fundamental (ν18) for three isotopic thiazoles. The direct impact on ν18 by isotopic substitution at C2 and C5 is observed. The combined rotational and high-resolution IR data allowed for an excellent fit of the Coriolis-coupled dyad of ν17 and ν13, which includes more than 60 nominal interstate transitions. Some of the measured resonant transitions are displaced by more than 30\xa0GHz. The least-squares fit yielded six Coriolis coupling terms ( G a , G a J , G a K , G b , G b J , and G b K ) and very accurate measurements of the ν17 and ν13 band origins, 603.8511589 (17) cm−1 and 611.2214645 (18) cm−1, respectively. Collectively, these data provide reliable spectroscopic constants that can be used to predict the rotational spectra of thiazole up to 360\xa0GHz.