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

Abstract

The structure and reactivity of p-CrOH(NH(3))(2) and p-CrOH(H(2)O)(NH(3)) 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(NH(3))(2) shows a sub-nanosecond lifetime, as determined by time-resolved LIF spectra, as a consequence of a hydrogen transfer process that results in NH(4)(NH(3)) as a reaction product. Substitution of NH(3) by H(2)O closes the reaction channel as evidenced by the absence of excited-state hydrogen transfer (ESHT) reaction products, (H(3)O(NH(3)) or NH(4)(H(2)O)) and results in a dramatic effect on the S(1) lifetime of the p-CrOH(H(2)O)(NH(3)) complex which rises to (12 +/- 2) ns. According to density functional theory calculations, the most stable isomer of the p-CrOH(H(2)O)(NH(3)) complex is a cyclic structure, in which H(2)O acts as the H acceptor of the phenolic OH group (c-OH-H(2)O-NH(3)). However, the ESHT process is energetically disallowed upon electronic excitation.