One-color two-photon and three-photon PFI-ZEKE spectra of trans-butadiene and trans-hexatriene

Abstract

Pulsed field ionization-zero-kinetic-energy (PFI-ZEKE) photoelectron spectra are measured for trans-butadiene, trans-hexatriene, and cis-hexatriene by one-color two-photon and one-color three-photon excitation of molecules into high-n Rydberg states. The excitation processes that lead to the ground state ions have been investigated. It has been suggested that the ground-state trans-butadiene, trans-hexatriene, and cis-hexatriene ions are produced via simultaneous multiphoton absorption processes in both the two-photon and three-photon PFI-ZEKE experiments. The frequencies of PFI-ZEKE bands obtained from two-photon absorption are essentially the same as those from three-photon absorption for trans-butadiene, trans-hexatriene, and cis-hexatriene. We have discussed symmetries of the Rydberg states that lead to the ground-state cation via two-photon and three-photon processes. The frequencies of several vibrations have been determined for the isolated-state trans-hexatriene and cis-hexatriene cations.