The relaxation of vibrationally excited AlO isolated in argon matrices at 18 K has been studied using an IR pump, optical probe double resonance experiment. At low AlO concentrations (ppm), the v″ = 1 state (975 cm −1) has a lifetime of 25 ms, a period which allows about one resonant energy hop among AlO molecules prior to decay. Addition of selected impurities decreases the lifetime dramatically and the resultant nonexponential decays are in good agreement with a Förster dipole—dipole VV transfer mechanism, assisted by coupling to host or local modes to absorb Δ E, the donor—acceptor energy mismatch. From concentration studies, microscopic constants are obtained for the AlO donor interaction with various acceptors. Dipole derivatives deduced from IR absorbance measurements are used with dipole moments in a theoretical coupling model of Lin and coworkers to deduce rates K d and K a at which Δ E is lost at the donor and acceptor sites. For polar acceptors such as NH 3, ND 3, and CH 2Cl 2, most of the excess energy is lost at the acceptor site. K a rates measured for NH 3 and ND 3 are in good accord with those predicted by Legay's empirical relation for VR relaxation involving local libration or rotation. For nonpolar acceptors C 2H 4, SF 6, C 2H 6, and CO 2, Δ E is dissipated at the AlO site by excitation of local/bulk translational modes and an exponential gap law ▪ is observed. In each of these molecules, relaxation is assumed to proceed through the IR active fundamental vibration nearest, but below, 975 cm −1. An exception to this appears to be CF 4, where relaxation is thought to occur not through the nearest ν 7 IR mode at 630 cm −1 but rather via a dipole-induced dipole coupling with the IR forbidden, but more nearly resonant ν 1 vibration at 904 cm −1.