Microcanonical (energy-dependent) rate constants for the c−HOCO → CO₂ + H (top) and c−HOCO + CO → CO₂ + HCO (bottom) reaction step on CO ice. The different solid lines represent different ergodic energy dissipation scenarios with n molecules accepting the reaction energy. The vertical dashed lines indicate fractions (0.1, 0.25, and 0.5) of the O + H reaction (red) and of half the energy of a Lymann alpha photon (blue); see text. The zero of energy is defined as the PES asymptote (i.e. no adsorption).