Applicability of resonant two photon ionization in supersonic beams to halogenated aromatic hydrocarbons

This work investigates problems encountered in the application of one color resonant two‐photon ionization 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 di‐distributed benzenes. In the case of para‐substituted compounds where there is little substituent group interacting ionization occurs efficiently at the S0 → S1 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 withdrawing properties of the substitutent groups thereby allowing reasonable predictions to be made regarding those types of subsdtituted benzenes which can be probed with R2PI.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/87501/2/620_1.pd