Photon-catalyzed unimolecular decomposition with large first-order rate constant

The second-order process, photon-catalyzed unimolecular decomposition (PCUD), is shown to be comparable to and sometimes larger than the first-order single-photon stimulated decomposition (SPSD) when the intermediate molecular transition is coherently saturated. Thus PCUD is a dominant, identifiable process even in the large class of molecular bound states with nearby continuum allowing SPSD, e.g., the halogen diatoms in the $B{0}^{+}u$ states. It may also be important in the multiphoton dissociation or ionization of molecules.