Multiphoton ionization and photoelectron spectroscopy of 1,3-trans-butadiene via its 3d pi Rydberg state

Resonance-enhanced multiphoton ionization (REMPI) and photoelectron spectro scopy (PES), have been used to study the (1)A(g)(3d pi) Rydberg state of 1, 3-trans-butadiene in the two photon energy range from 61 000 to 66 400 cm(- 1). The (1)A(g)(3d pi) spectrum is dominated by the nu (4)', nu (6z)', and nu (9)' vibrational modes, with some excitation of the nu (8)' mode, as wel l. Photoelectron spectroscopy shows that the dominant ionization pathways a re diagonal, i.e., they produce cations in the same vibrational level that was populated in the Rydberg state. Weaker off-diagonal ionization is also observed, with excitation of the nu (+)(4), nu (+)(6), and nu (+)(9) modes. The relative intensities of diagonal and off-diagonal PES bands are observ ed to be strongly dependent on the angle between the laser polarization and the detection axis. It is possible to use REMPI to generate state-selected cations, however, the nascent ions are quite efficiently photodissociated by the REMPI laser. (C) 2001 American Institute of Physics.