Three body photodissociation of the water molecule and its implications for prebiotic oxygen production

The provenance of oxygen on the Earth and other planets in the Solar System is a fundamental issue. It has been widely accepted that the only prebiotic pathway to produce oxygen in the Earth’s primitive atmosphere was via vacuum ultraviolet (VUV) photodissociation of CO 2 and subsequent two O atom recombination. Here, we provide experimental evidence of three-body dissociation (TBD) of H 2 O to produce O atoms in both 1 D and 3 P states upon VUV excitation using a tunable VUV free electron laser. Experimental results show that the TBD is the dominant pathway in the VUV H 2 O photochemistry at wavelengths between 90 and 107.4 nm. The relative abundance of water in the interstellar space with its exposure to the intense VUV radiation suggests that the TBD of H 2 O and subsequent O atom recombination should be an important prebiotic O 2 -production, which may need to be incorporated into interstellar photochemical models. Three-body dissociation of water, producing one oxygen and two hydrogen atoms, has been difficult to investigate due to the lack of intense vacuum ultraviolet sources. Here, using a tunable free-electron laser, the authors obtain quantum yields for this channel showing that it is a possible route to prebiotic oxygen formation in interstellar environments.