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

Abstract

This contribution summarizes recent experimental developments in coupling modern 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 À1 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 À1 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.

Infrared spectra of protonated polycyclic aromatic hydrocarbon molecules: Azulene

“…To this end, the IRMPD technique has successfully been applied to the IR spectroscopy of a broad variety of ions and ionic complexes, and the interested reader is referred to recent reviews for further details. 13,[37][38][39] The present work reports the IRMPD spectrum of protonated azulene, AzuH + . AzuH + is an isomer of protonated naphthalene, which is the prototypical polycyclic aromatic hydrocarbon molecule ͑PAH͒.…”

“…Two major IR photodissociation strategies have successfully been applied to AH + ions as has been reviewed recently. 13 The first technique employs modern, relatively low-intensity, optical parametric oscillator laser systems in the frequency range 800-4000 cm −1 to drive one-photon IRPD of AH + -L n cluster ions. 12 This approach is based on the evaporation of one or more of the weakly bound ligands upon resonant absorption of a single photon ͑messenger technique͒, 14 and has been applied to a variety of AH + -L n cluster ions, including A = benzene, [15][16][17][18] phenol, 12,19 fluorobenzene, 20 para-halogenated phenols, 21 toluene, 17 pyridine, 18 aniline, 22 imidazole, 23 various amino acids and peptides, 24 and neurotransmitters.…”

Laboratory Spectroscopy of Protonated PAH Molecules Relevant For Interstellar Chemistry

“…Recent progress in the development of efficient ion sources and sensitive IR spectroscopic techniques have allowed to obtain the first IR spectra of size-selected protonated aromatic molecules and their weakly-bound clusters in the gas phase by coupling tandem mass spectrometry with resonant vibrational photodissociation spectroscopy (Solca & Dopfer 2001;Solca & Dopfer 2003a). The application of these techniques to protonated aromatic molecules has been reviewed previously (Dopfer 2006). In this contribution, we summarize the results obtained in the past decade for a large variety of H + PAH ions, ranging from protonated benzene to protonated coronene.…”

Infrared spectra of the protonated neurotransmitter histamine: competition between imidazolium and ammonium isomers in the gas phase

“…The second major strategy involves IRMPD of strongly bound isolated ions using intense IR free electron lasers. 35,36,[57][58][59][60][61][62][63] In the IRMPD process, the ion absorbs in a noncoherent fashion sequentially multiple IR photons until the lowest dissociation threshold is reached. 36 In recent years, IRMPD has successfully been coupled to electrospray ionization (ESI) sources to spectroscopically characterize AH + ions derived from larger biomolecules 36,64-67 and polycyclic aromatic hydrocarbon molecules, [68][69][70][71] as well as metal-organic complexes.…”

“…35,36 The first technique involves single-photon dissociation of weakly bound cluster ions using table-top IR lasers based on difference frequency mixing or optical parametric oscillators. [37][38][39] This approach has initially been applied to protonated phenol [40][41][42] and benzene, 43,44 and since then to a large variety of other AH + ions.…”