Theoretical Spectroscopic Characterization at low Temperatures of C2H3NO and its Isomers

MOLEC 2016, Toledo (Spain), 11 - 16 September 2016Relevant astrophysical molecules of empirical formula C2H3NO are characterized using explicitly correlated coupled cluster methods (CCSD(T)-F12/AVTZ-F12). We present results for four species: the most stable methyl isocyanate (CH3NCO), as well as, methyl cyanate (CH3NCO), acetonitrile oxide (CH3CNO) and hydroxyacetonitrile (HOCH2CN). Whereas acetonitrile oxide is a linear C3v structure, the remaining isomers are non-rigid species derived from methyl or OH group torsions. The recently detected methyl isocyanate shows a very low torsional energy barrier (V3=16.2 cm-1). All the torsional energy levels lye over the barrier. Thus, the methyl group can be considered a free rotor. The ground vibrational state rotational constants have been calculated to be A0 =76164.32 MHz, B0 =4411.89 MHz and C0 =4254.58 MHz. Although, the rotational parameters are really dependent of the skeletal motions, our parameters are in a very good agreement with the experimental ones [1]. Methyl cyanate shows a more conventional behavior. In this case, V3= 364.84 cm-1. The rotational constants A0 =39089.80 MHz, B0 = 5314.78 MHz and C0 = 4816.35 MHz were determined in a very agreement with the experimental ones [2]. Hydroxyacetonitrile show two different conformers which energy separation is 1.5 kcal/mol. The hydroxyl group display internal rotation restricted by two energy barriers (Vt=540 cm-1 and Vg¿g=446.4 cm-1. Finally, we provide anharmonic frequencies, predicting possible Fermi interactions, centrifugal distortions constants and torsional transitions. These last were calculated variationally using a CCSD(T)-F12 potential energy surface.Peer Reviewe