Multiphoton Dissociative Ionization of Gas-Phase Styrene.

We performed multiphoton ionization of styrene molecules and observed the formation of styrene and benzene cations, the latter being reported for the first time in the multiphoton ionization of styrene. The formation of the benzene cation reveals an internal conversion from the S₁ state to the S₀ state, which occurs via a S₁/S₀ conical intersection at 4.66 eV above the minimum of the S₀ state. The present results indicate the position of this conical intersection to be energetically lower than the theoretically calculated value and also the previous experimental observation. The role of dissociative ionization of styrene in the formation of benzene cations in the atmosphere is discussed.