H-bonded network rearrangements in the S0, S1 and D0 states of neutral and cationic p-cresol(H2O)(NH3) complexes

Abstract

The H-bonded network rearrangements in the S0, S1 and D0 states of the neutral and cationic p-CreOH(H2O)(NH3) complexes were studied experimentally by means of (1 + 1)/(1 + 10 ) REMPI (Resonantly Enhanced MultiPhoton Ionization) and time resolved LIF (Laser Induced Fluorescence) spectroscopies combined with DFT (Density Functional Theory) calculations at the B3LYP/ 6-311G++(d,p) level. A comparison of the rearrangement process of the H-bonded network in the three states is given. Two cyclic H-bonded isomers were found on the S0 potential energy surface and the results indicate that the rearrangement in this state is unlikely at the temperature of the supersonic expansion due to the presence of a high-energy barrier (7503 cm1 ). On the other hand, the re-determination of the S1 excited state lifetimes confirms that neither the H-bonded rearrangement nor the excited state hydrogen transfer (ESHT) reaction takes place in the S1 state at the excitation energies of this work. Thus, it is concluded that the absorption of the second photon to reach the D0 state takes place from the S1 state of the cyclic-(OH–OH2–NH3) isomer. A preferential evaporation of H2O upon vertical ionization of the cyclic-(OH–OH2–NH3) isomer is observed which is consistent with a statistical redistribution of the internal energy. Nevertheless, our theoretical calculations suggest that initial excitation of the H-bonded network rearrangement modes may also play a role to leave the H2O molecule as a terminal moiety in a chain-(OH–NH3–OH2) + isomer. The reaction pathway for the solvent rearrangement involves a double proton transfer process with a very low energy barrier (575 cm1 ) that is overcome at the vertical ionization energy of the complex.