The infrared spectroscopy of hydrogen-bonded bridges: 2-pyridone-(water)(n) and 2-hydroxypyridine-(water)(n) clusters, n=1,2

The water-containing clusters of the two tautomers 2-hydroxypyridine (2HP) and 2-pyridone (2PYR) are studied in the hydride stretch region of the infr ared using the techniques of resonant ion-dip infrared spectroscopy (RIDIRS ) and fluorescence-dip infrared spectroscopy (FDIRS). The results on 2PYR-( water)(n) build on previous high-resolution ultraviolet spectroscopy [Held and Pratt, J. Am. Chem. Soc. 115, 9708 (1993)] on the n=1,2 clusters and th e infrared depletion spectra of Matsuda [J. Chem. Phys. 110, 8397 (1999)] o n the n=1 cluster. The 2PYR-W-2 FDIR spectrum reflects the consequences of extending and strengthening the H-bonded bridge between N-H and C=O sites i n 2PYR. The spectrum shows evidence of strong coupling along the bridge, bo th in the form of the hydride stretch normal modes and in the breadth of th e observed infrared transitions. RIDIR spectra of the 2HP-W-n clusters are compared with those of 2PYR-W-n in order to assess the spectroscopic conseq uences of forming the analogous water bridges in the lactim tautomer. Densi ty functional theory calculations are compared with the RIDIR spectra to de duce that the 2HP-W-n clusters are indeed water-containing bridge structure s closely analogous to their 2PYR counterparts. The IR spectra of the 2HP-W -n clusters bear a striking resemblance to those of 2PYR-W-n. Potential rea sons for the unusual breadth of the bridge XH stretches are discussed. (C) 2000 American Institute of Physics. [S0021-9606(00)00347-0].