Applications of third generation synchrotron radiation in vacuum ultra-violet (VUV) photoionization spectroscopy and dynamics

This thesis covers three major applications of high-resolution vacuum ultra-violet (VUV) photoionization based on the third generation synchrotron radiation (SR) facility at the Advanced Light Source (ALS) of Lawrence Berkeley National Laboratory (LBNL). (i) Synchrotron-based pulsed field ionization (PFI) photoelectron (PE) and photoelectron-photoion coincidence (PEPICO) studies have been performed productively for a series of important atmospheric and astrophysical molecules: H₂O, D₂O, NH₃, ND ₃, CH₄, CD₄, CH₃Br, CH₃I, CHF₂Cl, CHFCl₂, CHCl₃, CH₂Cl ₂, CH₂ClBr, C₂H₃Br and BCl₃. Accurate ionization energies (IE) and appearance energies (AE) measurements for the above molecules have provided reliable ion thermochemistry data and bond energies for theorists and applied chemists. Individual uni-molecular dissociative reaction dynamics have been discussed as well. (ii) Based on PFI-PEPICO technique, it has been evolved for absolute cross section measurements of ro-vibrationally state-selected ion-molecule reaction as PFI-photoelectron-secondary ion coincidence (PFI-PESICO) detection. This PFI-PESICO technique coupled with guided ion beam (GIB) method and a novel application of wired ion gate for the experimental set-up has been described in detail. Two successful demonstration reactions have been measured for the absolute integral cross sections of H ⁺2X,n⁺ =0-17,N⁺=1 +Ne→NeH⁺+H 1 H ⁺2X,n⁺ =0-17,N⁺=1 +Ar→ArH⁺/Ar⁺+H/H2 2 (iii) To explore photoionization beyond one photon process, two-color high-resolution scheme has been demonstrated. A unique high-repetition rate grazing-incidence infrared (IR) optical parametric oscillator (OPO) source has been introduced to match the pseudo-continuous tunable VUV synchrotron beam. The successful VUV-IR ionization spectrum of Ar has been recorded in the energy region between the ionization thresholds for Ar+(2P_3/2) and Ar+(2P _1/2) to illustrate the feasibility and efficacy of this scheme as a general approach for high-resolution two-color photoionization studies. A complicated molecular system C₂H₂ has been studied using IR-pump VUV-excitation scheme to observe the symmetry forbidden transition through an indirect perturbation pathway. Three Rydberg series converging to anti-symmetric vibrational excited ionic state in rotational resolution have been observed for the first time. IR-active ν₃ band and its Fermi Resonance combination band (ν₂ + ν₄ + ν₅) have been studied in adjacent rotational transitions. Interesting intramolecular vibrational energy redistribution has been addressed.