title: Structure, vibrational spectra, and unimolecular dissociation of gaseous 1-fluoro-1-phenethyl cations.
abstract: The multiple CF bond character of PhCFMe (+) ions has been examined by means of theory, vibrational spectroscopy of the gaseous ions, and unimolecular decomposition chemistry. Atoms in Molecules analysis of DFT wave functions gives a CF bond order of n = 1.25 (as compared with n = 1.38 for Me 2CF (+), relative to n = 1 for fluoromethane and n = 2 for diatomic CF (+)), which is consistent with calculations of adiabatic CF stretching frequencies (nu CF). Experimental gas phase IR spectra, recorded by means of resonant multiphoton dissociation (IRMPD) using a free-electron laser connected to an FTICR mass spectrometer, show good agreement with predicted band positions for five deuterated isotopomers of PhCFMe (+). Metastable ion decompositions of deuterated analogues of PhCFMe (+) show the same HF/DF loss patterns as those produced by IRMPD. The evidence supports the conclusion that PhCFMe ions retain structural integrity until they become sufficiently excited to dissociate, whereupon they undergo intramolecular hydrogen scrambling that is competitive with HF/DF expulsion. Relative rates of hydrogen transposition and unimolecular dissociation are extracted from relative experimental fragment ion abundances. The predominant decomposition pathway is inferred to operate via a five-center transition state, as opposed to a four-center transition state for HF loss from gaseous Me 2CF (+).
authors.affiliation: FOM Institute for Plasmaphysics Rijnhuizen, Edisonbaan 14, NL-3438 MN Nieuwegein, The Netherlands.
authors.forename: Jos
authors.initials: J
authors.lastname: Oomens
authors.forename: Elfi
authors.initials: E
authors.lastname: Kraka
authors.forename: Michael K
authors.initials: MK
authors.lastname: Nguyen
authors.forename: Thomas Hellman
authors.initials: TH
authors.lastname: Morton
mesh_terms: D002412:Cations / Q000737:chemistry; D004980:Ethane / Q000031:analogs & derivatives* / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D006845:Hydrocarbons, Fluorinated / Q000737:chemistry*; D013058:Mass Spectrometry / Q000379:methods; D008956:Models, Chemical; D015394:Molecular Structure; D013055:Spectrophotometry, Infrared / Q000379:methods; D014732:Vibration
chemical_list: D002412:Cations; D005740:Gases; D006845:Hydrocarbons, Fluorinated; C029999:fluoromethane; D004980:Ethane