Condensed and gaseous benzonitrile: ionic species formation and structural parameters

Abstract

Laboratory experiments were performed to evaluate benzonitrile (CN–Bz) under electron impact in the condensed phase by electron-stimulated ion desorption (ESID) and in the gas phase by ionization time of flight mass spectrometry with high mass resolution (EI-TOF-MS). This report focuses on the identification and quantification of the single and double charged ionic species from small to large masses initiated by radiolysis in the electron impact range of 12 eV to 2000 eV and desorption at 2300 eV electrons. The fragmentation of isolated CN–Bz in the gas phase is compared with the ejection of positive ions from the surface of condensed CN–Bz. The results highlight the dissociation, isomerization and formation of larger molecules and double charged metastable species. On the theoretical side, an automated global minimum (GM) search for low energy isomers was performed for selected ionic and dicationic species suggesting possible structures. Harmonic frequency calculations ensured that all structures represented a minimum at the potential energy surface. Based on data collected by spacecraft missions sent to the Saturn moon Titan, the presence of benzonitrile in the Titan atmosphere is discussed and suggests a low survival lifetime of the gaseous molecule at high altitudes, but its possible formation in haze aerosols.