Vibrational predissociation of the phenol–water dimer: a view from the water
The vibrational predissociation (VP) dynamics of the phenol–water (PhOH–H2O) dimer were studied by detecting H2O fragments and using velocity map imaging (VMI) to infer the internal energy distributions of PhOH cofragments, pair-correlated with selected rotational levels of the H2O fragments. Following infrared (IR) laser excitation of the hydrogen-bonded OH stretch fundamental of PhOH (Pathway 1) or the asymmetric OH stretch localized on H2O (Pathway 2), dissociation to H2O + PhOH was observed. H2O fragments were monitored state-selectively by using 2+1 Resonance-Enhanced Multiphoton Ionization (REMPI) combined with time-of-flight mass spectrometry (TOF-MS). VMI of H2O in selected rotational levels was used to derive center-of-mass (c.m.) translational energy (ET) distributions. The pair-correlated internal energy distributions of the PhOH cofragments derived via Pathway 1 were well described by a statistical prior distribution. On the other hand, the corresponding distributions obtained via Pathway 2 show a propensity to populate higher-energy rovibrational levels of PhOH than expected from a statistical distribution and agree better with an energy-gap model. The REMPI spectra of the H2O fragments from both pathways could be fit by Boltzmann plots truncated at the maximum allowed energy, with a higher temperature for Pathway 2 than that for Pathway 1. We conclude that the VP dynamics depends on the OH stretch level initially excited.