Photochemistry in the Early Solar System

摘要

Isotope-selective photodissociation of gaseous carbon monoxide is a well-known process in molecular clouds. This process may have been important in the early solar system, with the nascent Sun as the source of ultraviolet radiation. The consequent self-shielding gives rise to the non-mass-dependent oxygen isotope variations observed in primitive meteorites. This model implies that the solar oxygen isotope ratios, ~(18)O/~(16)O and ~(17)O/~(16)O, are about 5% smaller than those ratios in the Earth and other inner solar system bodies. A similar effect may also have occurred for nitrogen, through photolysis of N_2. These photochemical processes lead to disequilibrium chemistry in the formation of solid bodies in the Solar System.