15min:

C. J. GRUENLOH, GINA M. FLORIO AND T. S. ZWIER, Department of Chemistry, Purdue University, West Lafayette, IN 47907-1393.

The structures and dynamics of 2-hydroxypyridine-(water)_n clusters (with n=1 and 2) have been investigated using resonant two-photon ionization time-of-flight mass spectroscopy (R2PI-TOFMS), IR-UV hole-burning, and resonant ion-dip infrared spectroscopy (RIDIRS). The double resonance technique of RIDIRS provides both wavelength and mass selectivity in recording the hydride stretch infrared spectrum (2200 to 3800 cm^-1) of a chosen cluster. The RIDIR spectrum of 2HOP monomer contains a narrow transition at 3598 cm^-1, about 55 cm^-1 lower in wavenumber than those of the corresponding hydroxy groups in phenol and cis/trans 2-naphthol. This suggests the presence of a weak intramolecular H-bond. The spectra of 2HOP-(H₂O)₁-2 contain sharp free OH stretch transitions near 3715 cm^-1 and H-bonded OH stretch transitions in the 3100-3500 cm^-1 region, which are remarkably broad (approaching 100 cm^-1 in 2HOP-(H₂O)₂) and show distinct sub-structure indicative of strong coupling to background states. A comparison with the results of density functional theory calculations indicates that the water molecules in 2HOP-(H₂O)₁ and 2HOP-(H₂O)₂ form bridges between the OH and N groups of 2HOP, accepting a H-bond from the OH group and donating a H-bond to the nitrogen lone pair. Possible reasons for the unusual breadth of these transitions will be put forward.