Internal rotation and spin conversion of CH₃OH in solid para-hydrogen

The quantum solid para-hydrogen (p-H₂) has recently proven useful in matrix isolation spectroscopy. Spectral lines of compounds embedded in this host are unusually narrow, and several species have been reported to rotate in p-H₂. We found that a p-H₂ matrix inhibits rotation of isolated methanol (CH₃OH) but still allows internal rotation about the C-O bond, with splittings of the E/A torsional doublet in internal rotation-coupled vibrational modes that are qualitatively consistent with those for CH₃OH in the gaseous phase. This simplified high-resolution spectrum further revealed the slow conversion of nuclear spin symmetry from species E to species A in the host matrix, offering potential insight into nuclear spin conversion in astrophysical sources.