Penning Ionization of NCCN by Experiment and Theory: A Two-Dimensional Penning Ionization Electron Spectroscopic and Quantum Chemical Study

Abstract

Dicyanogen, NCCN, is generated for spectroscopic investigations on-line from rubeanic acid, mercury(II) cyanide, and cyanogen iodide and studied in the gas phase by two-dimensional Penning and He I photoelectron spectroscopies, as well as ab initio calculations. From spectroscopic data, the interaction between NCCN and He*(23S) atoms is deduced. The interaction potential for the similarly interacting NCCN−Li(22S) system is obtained from ab initio calculations at the CCSD/6-311++G** level. Experimental and calculated results show that the interaction potential is anisotropic around NCCN, is the most attractive in the nitrogen lone electron pair region, and gradually changes into repulsive as the N−C−He*(or Li) angle opens up to 90°. An unusual collision energy dependences of the partial ionization cross sections are observed, which is interpreted by the unusual interaction potential. For assisting experimental data and studying collision dynamics, classical trajectory calculations are performed for the Penning ionization of the NCCN−He*(23S) system. The spectroscopic investigations predict the existence of thermodynamically stable MLi radicals, and the structure and stability of NCCNLi isomers are calculated at the QCISD/6-311++G** level.