Multiphoton Dissociative Ionization of Gas-Phase Styrene

Area of Science:

• Physical Chemistry
• Chemical Physics
• Molecular Spectroscopy

Background:

• Multiphoton ionization (MPI) is a key technique for studying molecular electronic states and fragmentation pathways.
• Styrene, a common aromatic hydrocarbon, exhibits complex photochemistry upon ionization.
• Understanding benzene cation formation is crucial for atmospheric chemistry and astrochemistry.

Purpose of the Study:

• To investigate the formation pathways of styrene and benzene cations produced by multiphoton ionization of styrene.
• To characterize the energetic position of the S1/S0 conical intersection involved in benzene cation formation.
• To assess the implications of these findings for the role of dissociative ionization in atmospheric benzene cation production.

Main Methods:

• Multiphoton ionization (MPI) spectroscopy of styrene molecules.
• Analysis of fragment ion mass spectra to identify styrene and benzene cations.
• Determination of the energetic location of the S1/S0 conical intersection.

Main Results:

• Observation of both styrene and benzene cations during styrene MPI, with benzene cation formation reported for the first time.
• Evidence for internal conversion from the S1 to the S0 state via a S1/S0 conical intersection at 4.66 eV.
• The experimentally determined conical intersection energy is lower than previously reported theoretical and experimental values.
• Discussion of the potential role of styrene dissociative ionization in atmospheric benzene cation formation.

Conclusions:

• The study provides the first experimental evidence for benzene cation formation in styrene MPI, indicating a lower-than-expected conical intersection energy.
• These findings refine our understanding of styrene photochemistry and internal conversion processes.
• The results highlight the importance of considering dissociative ionization of styrene in atmospheric models for benzene cation formation.