Mass analyzed threshold ionization: structural information for a mass spectrum and mass information for ionic spectroscopy

Abstract

Mass analyzed threshold ionization spectroscopy is a technique for simultaneously recording a mass spectrum and an optical spectrum for each parent ion present. In this method a laser is tuned through the ionization continuum of the sample, while the instrument is set up to record a given mass only when the light is tuned to an ionization threshold. The presence of an ionization threshold is signaled by the presence of long-lived high Rydberg states which are field ionized after they are separated from directly produced ions. A reflectron mass spectrometer then provides mass information to go with the optical spectrum of the ions provided by scanning the laser. Vibrational structure of the ionic ground state is easiest to obtain, but future development may enable rotational information to be gained as well. The technique should find use in resolving isomeric ambiguity in mass spectra, in determining the structure of species present in mixtures, and for examining the photophysics of both the neutral and ionic states of the molecule of interest.