Internal Rotation and Spin Conversion of CH ₃ OH in Solid para-Hydrogen

Abstract

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.

The Infrared Spectrum of Protonated Ovalene in Solid Para-Hydrogen and Its Possible Contribution to Interstellar Unidentified Infrared Emission

“…The matrix-isolation system for mid-IR absorption and the p-H 2 converter used in this work have been described elsewhere (Lee et al 2006;Bahou et al 2012Bahou et al , 2014a. A gold-plated flat copper substrate, cooled to 3.2 K with a closedcycle helium refrigerator system (SHI, RDK-415D), served as both the matrix sample substrate and the mirror to reflect the incident mid-IR beam to the detector.…”

Spectral line shape profile of rovibrational transitions of CO embedded in p-H2 crystals studied by high resolution IR diode laser spectroscopy

“…[2][3][4][5] Concerning other molecules embedded in solid p-H 2 , HCl, 6 H 2 O, 7 CH 3 F, 8,9 CH 3 OH, 10 and recently CO ͑Ref. 11͒ have been reported.…”

Path integral molecular dynamics simulation of quasi-free rotational motion of CO doped in a large para-hydrogen cluster

“…On the other hand, in cryogenic para-hydrogen (p-H 2 ) condensed phases such as p-H 2 solid, some molecules (typically hydride molecules) are known to behave as if they are free rotors [4]. Thus, they can provide alternative trapping potentials to molecular qubits although the p-H 2 condensed phases have been studied mainly from the view point of high-resolution rovibrational spectroscopy of the dopants [4,5]. What make the environments unique are the small mass of p-H 2 and the weak van der Waals interactions; that is, the quantum-mechanical zero-point kinetic energy is comparable to the potential energy, resulting in a large fluctuation associated with the position of p-H 2 compared to its nearest-neighbor distance [6].…”