Combined High Resolution UV and Microwave Results: Structure of the Benzonitrile•Water Complex

High resolution ultraviolet (UV) and molecular beam Fourier transform microwave (MB FTMW) spectroscopy of the benzonitrile·water (BZNW) cluster were performed to measure cluster structures in the S0and S1states. The MW experiments provide additional information on the structure and the 14N-nuclear quadrupole coupling in the ground state So, the UV experiments on the dynamics in Si. The rotationally resolved sub-Doppler UV spectra of BZNW were measured by mass-selective resonance-enhanced two-photon ionization. For the first time this UV technique has been applied to hydrogen-bonded clusters. From the UV spectra the rotational constants are obtained by Correlation Automated Rotational Fitting. The MW spectra were analyzed with the model of a centrifugally distorted rotor including nuclear quadrupole coupling. A r0-fit of the water position within the cluster is performed. The water is found to be located with its oxygen nearly in the plane of benzonitrile (BZN). For S0(S1), the distance of the oxygen to the ortho hydrogen is r0= 2.477(4) Å (2.457(2) Å) and the angle to the ortho carbon-hydrogen bond 143.34(2)° (141.91(3)°). The structure differences in S1and S0can be explained by the structure changes of the BZN molecule. A line broadening, which points to a faster decay in Si upon clustering with the polar solvent, is observed for the BZNW cluster.