STRUCTURES AND VIBRATIONS OF PHENOL-$NH_{3}$ AND PHENOL-($NH_{3})_{2}$-CLUSTERS

Author Institution: Heinrich-Heine-Universit\""{a}t D\""{u}sseldorf, Institut f\""{u}r Physikalische Chemie und Elektrochemie I, Universit\""{a}tsstra\'{e}; Heinrich-Heine-Universit\""{a}t D\""{u}sseldorf, Institut f\""{u}r LasermedizinThe phenol-ammonia complexes have been investigated experimentally by two colour 1+1 resonance ionization (REMPI) and mass resolved hole burning spectroscopy and theoretically by ab initio methods at the HF/6-31G(d,p) and HF/6-31++G(d,p) level of theorey. With these theoretical methods the structures and vibrational frequencies of the clusters could be determined. By means of spectral hole burning, four bands in the low frequency region could be assigned to specific intermolecular vibrations of the 1:1 complex. Transitions arising from the threefold rotation of the $NH_{3}$ moiety could be correlated with calculated frequencies for this motion. Barriers of $43 cm^{-1}$ for the $S_{0}$ and $53 cm^{-1}$ for the $S_{1}$ state were obtained. Other strong bands in the one-color REMPI spectrum of the 1:1 cluster could be assigned to phenol-($NH_{3})_{2}$ by two-color experiments. The lowest frequency transition at $35545 cm^{-1}$ is tentatively assigned to pure electronic $S_{1}\leftarrow S_{0}$ transition. A progression of approximately $20 cm^{-1}$ is built upon this electronic origin, as well as on a transition at $265 cm^{-1}$. Every line within both progressions splits by about $2 cm^{-1}$. Hole burning spectroscopy shows that the splitted lines stem from different conformers of the cluster. For the calculated cyclic geometry of the cluster there are two possible conformers with the H-atom of the $N\cdot\cdot H\cdot\cdot N$ hydrogen bond lying above or below the ONN plane. The significance of cyclic structures in regard to intracluster proton transfer is discussed