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

Free-jet spectra and structure of o-, m- and p-dihydroxybenzenes

Analysis of the free-jet spectra of hydroquinone (para), catechol (ortho) and resorcinol (meta) shows the presence of multiple origins in each molecular spectrum which are interpreted as belonging to separate structural isomers.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/25500/1/0000041.pd

Excited state spectroscopy of para di-substituted benzenes in a supersonic beam using resonant two photon ionization

Excited state vibronic spectra of p-aminophenol, p-cresol, p-fluoroaniline, p-fluorophenol, hydroquinone and p-toluidine have been obtained using resonant two photon ionization supersonic beam mass spectrometry. Despite marked similarities in the spectra, notable differences exist and different para polyatomic substituents in the same molecule show vibronic evidence of their real molecular symmetry of C2[nu]. Expansion of the ring is also noted upon excitation in all cases. Further, it is now evident that the assignment of some vibronic bands historically interpreted as sequence structure must be reconsidered since molecules like hydroquinone are mixtures of cis and trans and others have a vibronic structure arising from the polyatomic nature of the substituents (c[function of (italic small f)]. CH3).Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/26444/1/0000532.pd

Multi-photon and electron impact ionisation studies of reactivity in adenine–water clusters

Multi-photon ionisation (MPI) and electron impact ionisation (EII) mass spectrometry experiments have been carried out to probe unimolecular and intermolecular reactivities in hydrated adenine clusters. The effects of clustering with water on fragment ion production from adenine have been studied for the first time. While the observation of NH4+ fragments indicated the dissociation of protonated adenine, the dominant hydration effects were enhanced C4H4N4+ production and the suppression of dissociative ionisation pathways with high activation energies. These observations can be attributed to energy removal from the excited adenine radical cation via cluster dissociation. Comparisons of MPI and EII measurements provided the first experimental evidence supporting hypoxanthine formation in adenine–water clusters via theoretically predicted barrierless deamination reactions in closed shell complexes

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

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."