Nuclear spin conversion of H, HO, and CH interacting with diamagnetic insulators

Yamakawa, Koichiro   ; Fukutani, Katsuyuki

A molecule including two or more hydrogen nuclei in the rotationally symmetric positions exists in nuclear spin isomers according to their resultant spin. Owing to the quantum statistics, the isomers occupy specific rotational states, which enables us to distinguish them by rotationally-resolved spectroscopy. Whereas the interconversion between the isomers are strictly forbidden in the isolated state, it is highly promoted in condensed systems. Focusing on simple and astronomically important molecules of H, HO, and CH, we review recent theoretical and experimental studies on the nuclear spin conversion proceeding on or in diamagnetic insulators. The fundamental difference between the conversion models of diatomic and polyatomic molecules is also clarified.