Hydrogen-bonding topologies of indole-(water)n clusters from resonant ion-dip infrared spectroscopy

A combination of resonant two-photon ionization, infrared-ultraviolet hole burning, and resonant ion-dip infrared spectroscopies are used to assign and selectively probe the hydrogen bonding topologies of indole-(water)(n) clusters with n=1,2. The indole-(water)(1) complex is confirmed to possess the N-H ... OH2 structure surmised from previous studies. However, the bands in the ultraviolet previously assigned to a pi H-bound indole-water complex are shown to be due instead to the indole-(water)(2) cluster in which the water dimer forms a H-bonded bridge between the N-H and aromatic pi clouds of indole. The implications of this reassignment for our understanding of the influence of H-bonding solvents on indole's fluorescence properties are discussed. (C) 1998 American Institute of Physics. [S0021-9606(98)02909-2].