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.

Keywords:

• 1,4-pentadiene
• photoionization
• photodissociation
• excitation energies

Acknowledgements

This work was financial supported by the DGAPA-UNAM, grants IN107310 and IN108009, PAPIIT grant IN107912, and CONACYT, grant 82521. The authors thank the technician support of A. Guerrero.