IR spectroscopic strategies for the structural characterization of isolated and microsolvated arenium ions

This contribution summarizes recent experimental developments in coupling modem sensitive IR spectroscopic techniques with selective mass spectrometric methods, which have allowed for the first time for the unambiguous structural characterization of isolated and microsolvated protonated aromatic molecules in the gas phase. The two major experimental strategies involve (i) single-photon IR photodissociation (IRPD) spectroscopy in a tandem quadrupole mass spectrometer using novel optical parametric oscillator (OPO) laser systems in the 2500-4000 cm(-1) range and (ii) IR multiphoton dissociation (IRMPD) spectroscopy in a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer using high-intensity free electron lasers (FEL) in the 500-2500 cm(-1) range. Both techniques offer complementary spectroscopic information, which is highlighted for the various isomers of protonated fluorobenzene, a simple prototype for protonated aromatic molecules. The analysis of the IR spectra provides unprecedented experimental insight into structure, energetics, and chemical reactivity of these fundamental reactive intermediates under isolated and controlled microsolvation conditions. Copyright (c) 2006 John Wiley & Sons, Ltd.