Vibrational spectroscopy of the F−·H2O complex via argon predissociation: photoinduced, intracluster proton transfer?

The mid-IR vibrational spectrum of the strongly bound F−·H2O complex is reported via predissociation of the size-selected F−·H2O·Arm (m=1–3) clusters. A weak, sharp band at 3690 cm−1 confirms that this species adopts the asymmetric arrangement typical of the heavier halides, while the band arising from the ionic H-bond (IHB) is shifted very far to the red of the free H2O bands (shift ∼800 cm−1). The observed band position is actually found in the region of the predicted `overtoneʹ of the H-bonded oscillator, where the OH stretching vibration occurs in a very strongly anharmonic O–H⋯F− potential surface in which the first excited vibrational level samples the HF–OH− proton transfer configuration.