Infrared photodissociation spectra of aniline(+)-M (M = thiophene, furan and phenol) are measured in the 2700-3700 cm(-1) region and analyzed by density functional theory calculations. Only a structure involving a pi-type hydrogen bond is found for aniline(+)-thiophene. Two structural isomers are identified for aniline(+)-furan and aniline(+)-phenol, which have either a pi-type or a sigma-type hydrogen bond, where an amino proton of aniline(+) interacts with the pi-electrons or the oxygen atom of the neutral molecules, respectively. The isomer with a sigma-type hydrogen bond is more stable for aniline(+)-phenol, while less stable for aniline(+)-furan. (C) 2003 Elsevier B.V. All rights reserved.