Experimental and theoretical study on the photoionization of styrene

Abstract

This study employed a vacuum ultraviolet synchrotron radiation source and reflectron time-of-flight mass spectrometry (TOF-MS) to investigate the photoionization and dissociation of styrene. By analyzing the photoionization mass spectrum and efficiency curve alongside G3B3 theoretical calculations, we determined the ionization energy of the molecular ion, appearance energy of fragment ions, and relevant dissociation pathways. The major ion peaks observed in the photoionization mass spectra of styrene correspond to C₈ H₈ ⁺ , C₈ H₇ ⁺ and C₆ H₆ ⁺ . The ionization energy of styrene is measured as 8.46 ± 0.03 eV, whereas the appearance energies of C₈ H₇ ⁺ and C₆ H₆ ⁺ are found to be 12.42 ± 0.03 and 12.22 ± 0.03 eV, respectively, in agreement with theoretical values. The main channel for the photodissociation of styrene molecular ions is the formation of benzene ions, whereas the dissociation channel that loses hydrogen atoms is the secondary channel. Based on the experimental results and empirical formulas, the required dissociation energies (E_d ) of C₈ H₇ ⁺ , C₈ H₆ ⁺ and C₆ H₆ ⁺ are calculated to be (3.96 ± 0.06), (4.00 ± 0.06) and (3.76 ± 0.06) eV, respectively. Combined with related thermochemical parameters, the standard enthalpies of formations of C₈ H₈ ⁺ , C₈ H₇ ⁺ , C₈ H₆ ⁺ and C₆ H₆ ⁺ are determined to be 964.2, 1346.3, 1350.2 and 1327.0 kJ/mol, respectively. Based on the theoretical study, the kinetic factors controlling the styrene dissociation reaction process are determined by using the Rice-Ramsperger-Kassel-Marcus (RRKM) theory. This provides a reference for further research on the atmospheric photooxidation reaction mechanism of styrene in atmospheric and interstellar environments.

Keywords: dissociative mechanism; photoionization; styrene; synchrotron radiation.