Effect of the intermolecular hydrogen bond conformation on the structure and reactivity of the p-cresol(H2O)(NH3) van der Waals complex

The structure and reactivity of p-CrOH(NH3)(2) and p-CrOH(H2O)(NH3) complexes were studied using mass-resolved one-colour resonance-enhanced multi-photon ionization and laser-induced fluorescence (LIF) spectroscopy together with DFT calculations. At the excitation energy of this work, the S-1 state of p-CrOH(NH3)(2) shows a sub-nanosecond lifetime, as determined by time-resolved LIF spectra, as a consequence of a hydrogen transfer process that results in NH4(NH3) as a reaction product. Substitution of NH3 by H2O closes the reaction channel as evidenced by the absence of excited-state hydogen transfer (ESHT) reaction products, (H3O(NH3) or NH4(H2O)) and results in a dramatic effect on the S-1 lifetime of the p-CrOH(H2O)(NH3) complex which rises to (12 +/- 2) ns. According to density functional theory calculations, the most stable isomer of the p-CrOH(H2O)(NH3) complex is a cyclic structure, in which H2O acts as the H acceptor of the phenolic OH group (c-OH-H2O-NH3). However, the ESHT process is energetically disallowed upon electronic excitation.