Molecular tunneling and pumping effects in low temperature MBCO recombination

Recombination of carbonmonoxide after photodissociation has been studied by Mössbauer spectroscopy at 4.2 K and in the low temperature region, where tunneling effects play an important role in rebinding. We interpret the kinetic results in terms of a radiationless nonadiabatic multiphonon transition, which leads to a uniform description for all temperatures. Prolonged illumination at low temperature results in pumping into long-living states.