The thermal and photochemical properties of CH3ONO adsorbed on Ag(111), with and without a thick spacer layer of hexane, C6H14, are described. Angle-resolved time-of-flight measurements of NO ejected during photolysis at 248 and 351 nm exhibit trimodal velocity distributions. Two of the components are wavelength dependent and nonthermal, and are modeled as NO ejection with and without partially thermalizing collisions with surrounding species. The third component of the distribution is wavelength independent and characterized by the bulk temperature of the adsorbate-substrate system. These three components are present for all coverages of CH3ONO, submonolayer to multilayer, and persist even when there is a spacer of C6H14. The photochemistry is dominated by direct excitation of CH3ONO; there is no evidence for NO ejection as the result of substrate excitation. Comparing NO time-of-flight distributions for 1 monolayer (ML) of CH3ONO on clean Ag(111) to those for 1 ML on a thick layer of C6H14, evidences substrate involvement in the dynamics of nascent NO.