Experiments on the infrared multiphoton dissociation of the furan cation show the decay pattern to be dominated by a single photofragment, C3H4+. A second reaction pathway, leading to C2H2O+, that has an energy barrier within 1 hv (similar to 0.13 eV) of that for C3H4+, is almost completely absent. A theoretical model of the behaviour of ions within the trap reproduces these observations and shows that, within the timescale of the experiment, reactive ions acquire just sufficient photons to promote the lowest energy pathway. (c) 2005 Elsevier B.V. All rights reserved.