Vibrational spectroscopy of intermediates in benzene-to-pheno conversion by FeO+.

Gas-phase FeO(+) can convert benzene to phenol under thermal conditions. Two key intermediates of this reaction are the HO-Fe-C(6)H(5) insertion intermediate and Fe(+)(C(6)H(5)OH) exit channel complex. These intermediates are selectively formed by reaction of laser ablated Fe(+) with specific organic precursors and are cooled in a supersonic expansion. Vibrational spectra of the sextet and quartet states of the intermediates in the O-H stretching region are measured by infrared multiphoton dissociation (IRMPD). For Fe(+)(C(6)H(5)OH), the O-H stretch is observed at 3598 cm(-1). Photodissociation primarily produces Fe(+) + C(6)H(5)OH; Fe(+)(C(6)H(4)) + H(2)O is also observed. IRMPD of HO-Fe-C(6)H(5) mainly produces FeOH(+) + C(6)H(5) and the O-H stretch spectrum consists of a peak at approximately 3700 cm(-1) with a shoulder at approximately 3670 cm(-1). Analysis of the experimental results is aided by comparison with hybrid density functional theory computed frequencies. Also, an improved potential energy surface for the FeO(+) + C(6)H(6) reaction is developed based on CBS-QB3 calculations for the reactants, intermediates, transition states, and products.