Investigations of OH–N- and NH–O-type hydrogen-bonded clusters by UV laser spectroscopy Original Research Article

Resonant two-photon ionization spectra of OH–N hydrogen-bonded phenol–ammonia clusters PhOH(NH3)n up to n=4 were recorded via the (NH3)nH+ fragments of the proton transfer yield (PTY) spectroscopy. Under one-color conditions proton transfer already takes place for the 1:1 cluster. For the n=2 cluster the fragment spectrum is of much higher quality than the two-color ionization and the hole burning spectra. Resonant S1 spectra of the clusters with n>2 could be measured for the first time using PTY spectroscopy. Water clusters of benzotriazole have been investigated as NH–O hydrogen bond model. The monomer is interesting because its intramolecular proton transfer leads to the existence of two tautomers. While for the ground state an almost complete vibrational assignment is presented, the S1 spectra are much more difficult to interpret. By spectral hole burning it could be shown, that all bands in the excitation spectrum between the electronic origin at 34917.8 and 0, 0+1200 cm−1 belong to the 2H tautomer. The n=1, 2 water clusters of this tautomer are blue-shifted by 121.4 and 131.5 cm−1 relative to the monomer. The clusters with one and two H2O moieties both show two equivalent band systems, that can be traced back to a dominant vibration considerably affecting the spectra.