| A photoion-photoelectron apparatus has been constructed for photoion and photoelectron spectroscopic studies allowing for high-resolution photoion and photoelectron spectroscopic studies of polyatomic molecules trans -2-butene (trans-CH3CH=CHCH3), cis-2-butene, (cis-CH3CH=CHCH3), trans-1-bromopropene (trans-CH3CH=CHBr), cis-1-brompropene (cis-CH3CH=CHBr) and trichloroethene, (ClCH=CCl2) using tunable vacuum ultraviolet (VUV) and infrared (IR) lasers. Coherent VUV laser radiation is generated via nonlinear four-wave frequency mixing techniques, while IR laser light is generated via an optical parametric oscillator/amplifier based on difference-frequency mixing. The high-resolution photoelectron techniques employed are pulsed field ionization-photoelectron (PFI-PE) spectroscopy and photo-induced Rydberg ionization (PIRI) spectroscopy. The single-photon VUV-PFI-PE spectra of trans -2-butene, cis-2-butene, trans-1-bromopropene, and cis-1-bromopropene have been measured, yielding highly precise ionization energies and vibrational frequencies of the corresponding cations. The VUV-IR-PIRI detection scheme is used to probe the high-frequency vibrational modes associated with the symmetric and asymmetric C--H stretching motions in trans-CH3CH=CHCH3 + and ClCH=CCl2+, which cannot be observed in VUV-PFI-PE spectroscopic studies because of the limitation of negligible Franck-Condon factors. We show that by exciting the neutral molecule to a vibrational state prior to VUV photoionization, state-selected and state-to-state photoionization cross sections can be obtained. As a demonstration experiment, we have obtained the frequency for the nu12 (C--H stretching) mode of ClCH=CCl2 by IR-VUV-PFI-PE-depletion and IR-VUV-photoion measurements. By fixing the IR laser at the nu12 frequency followed by VUV-PIE measurements, we have determined the relative state-to-state photoionization cross sections for the processes, ClCH=CCl2+(nu 12+ = 1) ClCH=CCl2(nu12 = 1), ClCH=CCl2+ ← ClCH=CCl2, and ClCH=CCl 2+ ← ClCH=CCl2(nu12 = 1), where ClCH=CCl2 and ClCH=CCl2+ are in their vibrational states. |
