[en] The first experiments in which well defined waveguided radiation has been used to produced infrared multiphoton dissociation are reported. The waveguide used was of the cylindrical dielectric type. Excitation of the EH₁₁ waveguided mode by pulsed CO₂ laser radiation was confirmed by comparison of the diffraction pattern of the radiation emanating from the guide with theoretical calculations. Yields for the isotope selective multiphoton dissociation of deuterated trifluoromethane in the waveguide cell were compared with yields obtained previously using a conventional dissociation cell. Enhancements in yield in the waveguide dissociation cell of up to two orders of magnitude were measured. (author)