Journal of Physical Chemistry A, Vol.111, No.49, 12363-12371, 2007
Isotopomeric conformational changes in the anisole-water complex: New insights from HR-UV spectroscopy and theoretical studies
Resonance enhanced multiphoton ionization and rotationally resolved S, So electronic spectra of the anisole-(H2O)-H-2 complex have been obtained. The experimental results are compared with high level quantum mechanical calculations and with data already available in the literature. Quite surprisingly, the equilibrium structure of the anisole-(H2O)-H-2 complex in the So state shows some non-negligible differences from that of the isotopomer anisole-(H2O)-H-1 complex. Actually, the structure of the deuterated complex is more similar to the corresponding structure of the anisole-(H2O)-H-1 complex in the S, state. In anisole-water, two equivalent H(D) atoms exist as revealed by line splitting in the rotationally resolved spectra. It is possible to suggest a mechanism for the proton/deuteron exchange ruled by a bifurcated transition state for the exchange reaction, with both water hydrogen atoms interacting with the anisole oxygen atom. From the analysis of all of the available experimental data and of computational results, we can demonstrate that in the S 1 excited state the hydrogen bond in which the water molecule acts as an acid is weaker than in the electronic ground state but is still the principal interaction between water and the anisole molecules.