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In this paper the conformational landscape of amphetamine in the neutral ground state is examined by both spectroscopy and theory. Several spectroscopic methods are used: laser-induced fluorescence (LIF), resonance-enhanced two-photon ionization (R2PI), dispersed fluorescence and IR/R2PI hole burning spectroscopy. The latter two methods provide for the first time vibrationally resolved spectra of the neutral ground state of dl -amphetamine and the amphetamine–(H 2 O) 1,2 complexes. Nine stable conformers of the monomer were found by DFT (B3LYP/6-311++G(d,p)) and ab initio (MP2/6-311++G(d,p)) calculations. For conformer analysis the vibrations observed in the IR/R2PI hole burning and dispersed fluorescence spectra obtained from single vibronic levels (SVLF) of a selected conformer were compared with the results of an ab initio normal mode analysis. By this procedure three S 0 → S 1 transitions in the R2PI spectrum were assigned to three different conformer structures. Another weak transition earlier attributed to another conformer could be assigned to a vibronic band of one of the three conformers. Furthermore spectra of amphetamine–(H 2 O) 1,2 are tentatively assigned.

The vibronic spectra of the S 0 and S 1 state of chlorobenzene have been analyzed via laser induced fluorescence spectroscopy. The ground state frequencies were determined by dispersed fluorescence and comparison with ab initio calculations on the MP2 and B3LYP (6-311G(d,p)) level. Additional complete active space self-consistent field calculations (6-311G++(d,p)) have been carried out for theoretical description of the S 1 state.

The phenol molecule has been chosen to demonstrate how dispersed fluorescence spectroscopy can be used to assign hot bands, i.e. vibronic transitions starting from the vibrationally excited electronic ground state. The procedure outlined in this paper provides important information on fundamental out-of-plane vibrations in the electronic excited S1 state that are not observed in jet-cooled spectra. The results obtained lead to a new interpretation of the most intense hot bands in the UV absorption spectrum of phenol. We derive vibrational frequencies for the modes 10b1, 10b1 and 41 (Varsanyi's nomenclature) which are different from those given in the literature.

Phenol(CH 3 COOH) n clusters are studied by laser spectroscopy up to n =4 and by ab initio calculations on the Hartree–Fock/6-31G(d,p) level up to n =2. The resonant two-photon ionization (R2PI) spectra do not show any intense signal belonging to phenol(CH 3 COOH) 1 in contrast to the corresponding cluster with formic acid. IR–UV double-resonance and dispersed fluorescence spectra point to a geometry of the n =2 (3) cluster where the phenol molecule acts as proton donor bound to the acetic acid dimer (trimer). Other isomers like a cyclic arrangement as in phenol(HCOOH) 2 are discussed.

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.

Phenol(H 2 O) n clusters have been studied in the electronic ground state by dispersed fluorescence spectroscopy and in the electronically excited state by means of two-color resonant two-photon ionization (R2PI), spectral hole burning and rotationally resolved laser-induced fluorescence. Resonant spectra up to a cluster size of n =12 have been obtained by two-color R2PI under `soft' ionization conditions. The analysis of spectral shifts and of the intermolecular vibrations in both electronic states is used to assign structures for these bi-, tri- and (partially) tetracoordinated hydrogen bonded systems, which may be comparable to H-bond-deficient water structures at the surface of liquid water and ice.