Deuterium enrichment of interstellar methanol is reproduced experimentally for the first time via grain-surface H-D substitution in solid methanol at an atomic D/H ratio of 0.1 .
Although previous gas-grain models successfully reproduce the deuterium enrichments observed in interstellar methanol molecules ( D/H of up to 0.4 , compared to the cosmic ratio of \sim 10 ^ { -5 } ) , the models exclusively focus on deuterium fractionation resulting from the successive addition of atomic hydrogen/deuterium on CO .
The mechanism proposed here represents a key route for deuterium enrichment that reproduces the high observed abundances of deuterated methanol , including multiple deuterations .