Chapter 19 - Spectroscopy and Dynamics of Neutrals and Ions by High-Resolution Infrared–Vacuum Ultraviolet Photoionization and Photoelectron Methods

Abstract

Vacuum ultraviolet (VUV) photoion–photoelectron spectroscopy represents a major technique for the study of photoionization dynamics and obtaining energetic and spectroscopic information of neutrals and ions. By using a broadly tunable infrared (IR) optical parametric oscillator laser and a comprehensive tunable vacuum ultraviolet (VUV) laser, together with the supersonic molecular beam and pulsed-field ionization (PFI) detection techniques, we have demonstrated an array of novel two-color IR–VUV and VUV–IR photoion–photoelectron methods. In addition to IR–VUV–PFI–PE measurements, the combination of IR and VUV laser excitations has given rise to a series of new photoionization methods. The isomeric and conformation sensitivity of IR excitation and detection sensitivity of VUV photoionization, together with the long lifetimes of IR excited rovibrational states and VUV excited high-n Rydberg states, make the combination of IR and VUV excitations ideal for two-color spectroscopic and photoionization dynamics probes of polyatomic species and their ions. Selected experiments are presented to illustrate the principles, information contents, and unique capabilities of these IR–VUV and VUV–IR photoionization methods. IR–VUV–PI and IR–VUV–PFI–PE methods have been well proven to be generally useful high-resolution techniques for spectroscopic studies of neutrals and ions. High-resolution VUV–IR–PIRI measurements have not been made.