VUV photoionization and dissociative photoionization of o-xylene: experimental and theoretical insights

The photoionization and dissociative photoionization of o-xylene have been studied using synchrotron radiation vacuum ultraviolet light with the photon energy in the range of 8.0–13.0 eV. The ionization energy of o-xylene and the appearance energies for the main fragment ions $$\hbox {C}_{\mathrm {8}}\hbox {H}_{\mathrm {9}}^{+}$$ , $$\hbox {C}_{\mathrm {7}}\hbox {H}_{\mathrm {7}}^{+}$$ and $$\hbox {C}_{\mathrm {6}}\hbox {H}_{\mathrm {6}}^{+}$$ were determined to be 8.45, 11.08, 11.47 and 11.17 eV, respectively, with photoionization efficiency spectra (PIES). Three dissociation pathways of parent ions are investigated by experimental photoionization and the quantum-chemical calculations. The fragment ions $$\hbox {C}_{\mathrm {7}}\hbox {H}_{\mathrm {7}}^{\mathrm {+}}$$ derived from parent ions involved hydrogen atom transfer rather than direct dissociation. Particularly, detailed mechanisms of dissociation $$\hbox {C}_{\mathrm {6}}\hbox {H}_{\mathrm {6}}^{+}$$ are presented for the first time in this work. In addition, the geometries of the intermediates (INTs), transition states (TSs) and products have been performed at B3LYP/6-311 $$+ \,+$$ G (d, p) level. The mechanisms of dissociative photoionization of o-xylene and the INTs and TSs involved are discussed in detail.