Penning ionization electron spectroscopic and Ab Initio study of the interaction and ionization of HNCO and HNCS with He*(2³S) metastable and Li(2²S) ground state atoms

The electronic structure and ionization of HNCO and HNCS were studied in the gas phase by two-dimensional Penning and He I photoelectron spectroscopies. From experimental data the anisotropy of the interaction between molecules (M) and He*(2³S) atoms were deduced. The interaction potential for the similarly interacting M-Li(2²S) system was obtained from ab initio calculations at the CCSD(fc)/6-311++G** level. Experimental and calculated results showed that the interaction potential was attractive in the π orbital region of molecules and in the terminal oxygen lone electron pair region of HNCO, and the interaction was repulsive around the hydrogen atom. From the anomalies in the experimental results and from theoretical calculations, the breakdown of the MO picture for ionization of HNCS in the 15-20 eV region was concluded. The spectroscopic investigations predicted the existence of thermodynamically stable MLi radicals, and the structure and stability of HNCOLi and HNCSLi were calculated at the QCISD(fc)/6-311++G** level.