RESUMEN
The first spectroscopic observation of the previously unknown species HSiNCO has been reported. HSiNCO was generated by the fragmentation of trimethylsilylisocyanate with a high-voltage discharge source. The 0(0)(0) band of the A (1)A(")-X (1)A(') transition has been recorded with full rotational resolution using laser-induced fluorescence spectroscopy and ground and excited state rotational and centrifugal distortion constants determined. Ten additional vibrational bands belonging to HSiNCO have also been observed in the laser-induced fluorescence spectrum and have been assigned based on predicted anharmonic vibrational frequencies. Due to the large change in geometry upon excitation, a number of axis-rotation peaks have been observed in the 0(0)(0) band and the axis-rotation angle (theta(T)) has been estimated to be 0.6 degrees +/-0.2 degrees. Dispersed fluorescence spectroscopy has been carried out and nu(8) (the N-C-O out-of-plane bending mode) and a number of overtones of nu(4) (the Si-H wagging mode) have been observed in the ground electronic state.
RESUMEN
The first spectroscopic investigation of the A1A''-X1A' transition of HSiNC has been reported. The 0(0)(0) band of the A1A''-X1A' transition has been rotational resolved using laser-induced fluorescence spectroscopy, and ground- and excited-state rotational and centrifugal distortion constants were evaluated. Ten additional vibrational bands belonging to HSiNC have also been observed in the laser-induced fluorescence spectrum and have been assigned based on predicted anharmonic vibrational frequencies. Because of the large change in geometry upon excitation, a number of axis-rotation peaks have been observed in the 0(0)(0) band, and the axis-rotation angle (thetaT) has been estimated to be 1.0 +/- 0.2 degrees. Dispersed fluorescence spectroscopy has also been carried out, and a number of overtones of the nu3 fundamental (Si-H wagging mode) have been observed in the ground state, and its anharmonic parameter (x(e)) was evaluated.
RESUMEN
Ab initio methods have been used to study the lowest lying [H, Si, N, C, O] isomers, which are of astrochemical interest. Over 20 [H, Si, N, C, O] isomers in the 1A' electronic state have been investigated at the MP2/aug-cc-pVTZ level of theory. Of these, the seven lowest isomers have been further investigated using different levels of theory, including B3LYP and QCISD(T). It has been found that the relative energies of the isomers in their ground electronic state (1A') are very dependent on the level of theory used with either the cis-HOSiCN or cis-HOSiNC isomers being the lowest in energy. Overall, the four lowest isomers are within 6 kcal/mol of each other, and a further three isomers are less than 15 kcal/mol higher in energy than the lowest lying isomer, including HSiNCO, which has recently been detected spectroscopically. Natural bond analysis has been carried out on the ground electronic states of the seven lowest lying isomers to examine their electronic structure. The enthalpies of formation of the seven lowest isomers have also been evaluated using the G3MP2 and G3B3 multilevel methods and show that the isomers are relatively thermodynamically stable. The structures and energies of lowest lying 1A'' and 3A'' electronic states of these isomers have also been investigated and show that for most of the isomers the optimized structures in these excited electronic states correspond to a transition state structure.