A novel experimental technique is described in which radiation from a free electron laser is used to measure infrared spectra of gas-phase cluster ions via vibrational predissociation of the corresponding ion-messenger atom complexes. The weakly bound complexes are formed in a temperature-controllable, radio frequency ion trap. This technique is applied to the study of the vibrational spectroscopy of the monovanadium oxide cluster cations VO+, VO2+, and VO3+. (C) 2003 American Institute of Physics.