title: Hydrogen bond induced HF elimination from photoionized fluorophenol dimers in the gas phase.
abstract: In this paper, we report finding of a remarkable chemical effect of hydrogen bonding, elimination of hydrogen fluoride (HF) from the hydrogen bonded dimers of 2-fluorophenol (2-FP) and 3-fluorophenol (3-FP), in a supersonic jet expansion upon multi-photon ionization using 4th harmonic wavelength (266 nm) of a Q-switched Nd:YAG laser, and the reaction has been probed by time-of-flight mass spectrometry. No HF elimination is observed to occur by such means from the monomer of 3-FP, but it occurs with a small yield from the monomer of 2-FP. On the other hand, upon dimerization the reaction is triggered on for 3-FP, and for 2-FP it becomes so facile that no intact dimer cation survives and only the HF eliminated product ion appears in the mass spectra. Electronic structure calculation shows that in the cationic ground (D0) state, although the reaction for 2-FP dimer is exothermic, the associated barrier is significantly high (2.75 eV) and for its occurrence, absorption of three photons (2+1 type) is required. However, the reaction is predicted barrierless in the intermediate S1state of this dimer, and HF loss dimer cation mass peak could appear in the mass spectrum due to an effective two-photon (1+1) ionization process. In the case of 3-FP dimer, the energy barriers both in S1(neutral) and D0(ionic) states are high, and it is suggested that for occurrence of HF elimination, dimer cation needs to absorb an additional photon. For facilitation of HF loss from this dimer cation, a rearrangement of the geometry and formation of an intermediate adduct have been suggested, and it is argued that the latter could be produced by nucleophilic attack of the neutral moiety at the ortho site of the cationic counterpart.
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, 2A Raja S C Mullick Road, Jadavpur, Kolkata 700032, India.
authors.forename: Piyali
authors.identifier: 0000000338285622
authors.initials: P
authors.lastname: Chatterjee
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, 2A Raja S C Mullick Road, Jadavpur, Kolkata 700032, India.
authors.forename: Arup K
authors.identifier: 0000000212364464
authors.initials: AK
authors.lastname: Ghosh
authors.affiliation: Department of Physical Chemistry, Indian Association for the Cultivation of Science, 2A Raja S C Mullick Road, Jadavpur, Kolkata 700032, India.
authors.forename: Tapas
authors.identifier: 0000000252923873
authors.initials: T
authors.lastname: Chakraborty