APPLICABILITY OF RESONANT TWO PHOTON IONIZATION IN SUPERSONIC BEAMS TO HALOGENATED AROMATIC HYDROCARBONS

Abstract

Author Institution: Department of Chemistry, University of Michigan; Department of Chemistry, University of MichiganThis work investigates problems encountered in the application of one color resonant two-photoionization as an ionization source in supersonic beam mass spectroscopy. Of particular interest is the fact that photons of one color may not provide sufficient energy to cause ionization even when the laser source is tuned to an excited vibronic molecular state. We have therefore correlated trends in ionization potential with molecular structure for simple systems, specifically, halogenated aniline, phenol and toluene derivatives and mono- and disubstituted benzenes. In the case of para-substituted compounds where there is little substituent group interaction ionization occurs efficiently at the $S_{q} \to S_{1}$ origin, provided ultrafast processes are not active as in the case of iodo substituted benzenes. Many ortho compounds, however, are found not to ionize efficiently. This is probably due to a combination of coulombic and steric interactions which result in an increase in ionization potential. These types of effects have been qualitatively related to the electron releasing and with-drawing properties of the substituent groups thereby allowing reasonable predictions to be made regarding those types of substituted benzenes which can be probed with R2PI."