Statistical ortho-to-para ratio of water desorbed from ice at 10 kelvin

Abstract

Water isomers hide their origin H 2 O exists in two spin isomers, ortho and para, in a ratio of 3:1 at room temperature. Some astronomical observations have found water with a ratio of less than 3, thought to be due to water being photodesorbed from ice that had been formed at very low temperatures (≾30 K). Hama et al. tested this idea in the laboratory, by forming water ice at low temperature and then photodesorbing it to measure the ortho:para ratio. They found a ratio of 3, even at 10 K. Thus, another explanation for the low ratios in some astronomical objects must be found. Science , this issue p. 65