Excitation energies and multiphoton dissociation–ionization of 1,4-pentadiene at 266 and 355 nm

Abstract

The photodissociation (PD) and photoionization (PI) of 1,4-pentadiene (PDE), which result in the absorption of multiple photons, were studied both experimentally and theoretically. The PD and PI ions were the result of the interaction of a cooled molecular beam of PDE with laser radiation of wavelengths 266 and 355 nm, measured using a time of flight (TOF) mass spectrometer. There are several differences in the ionization patterns, with the wavelength as a common characteristic in the absence of the parent ion, and on the possible dissociation of the neutral species such as C2H3 and C3H5, which then dissociates and ionizes. To interpret the results, the potential energy surface (PES) of PDE was calculated. Using time-dependent density functional theory (TD-DFT), the excitation energies and potential energy surfaces along the two main dissociative coordinates, namely, C2–C3 and C3–H, were also calculated. Possible mechanisms responsible for the formation of the observed ions are proposed: hydrogen loss, molecular hydrogen formation, simple C–C dissociation, total deprotonation and hydrogen transposition.