Condensed and gaseous benzonitrile: ionic species formation and structural parameters.

Area of Science:

• Physical Chemistry
• Astrochemistry
• Mass Spectrometry

Background:

• Benzonitrile (CN-Bz) is a molecule of interest in astrochemical studies, particularly concerning its potential presence in extraterrestrial atmospheres like Titan's.
• Understanding the behavior of benzonitrile under electron impact is crucial for interpreting experimental data and atmospheric models.

Purpose of the Study:

• To investigate the fragmentation and ionization of benzonitrile (CN-Bz) under electron impact in both gas and condensed phases.
• To identify and quantify single and double charged ionic species formed from benzonitrile radiolysis.
• To explore the potential formation and atmospheric lifetime of benzonitrile on Titan.

Main Methods:

• Electron-stimulated ion desorption (ESID) for condensed phase analysis.
• High-resolution ionization time-of-flight mass spectrometry (EI-TOF-MS) for gas phase analysis.
• Computational methods including global minimum (GM) search and harmonic frequency calculations for theoretical structure elucidation.

Main Results:

• Identification and quantification of single and double charged ionic species of benzonitrile across a wide electron impact energy range.
• Comparison of gas-phase fragmentation with condensed-phase ion ejection, revealing dissociation and isomerization pathways.
• Observation of larger molecule formation and double-charged metastable species.
• Theoretical modeling suggested possible structures for ionic and dicationic species.

Conclusions:

• Benzonitrile exhibits complex fragmentation and isomerization under electron impact.
• The study provides insights into the potential presence and rapid degradation of benzonitrile in Titan's upper atmosphere.
• Benzonitrile may form in Titan's haze aerosols, despite its low survival lifetime as a gas.