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

Area of Science:

• Quantum Solid-State Spectroscopy
• Molecular Spectroscopy
• Astrochemistry

Background:

• Para-hydrogen (p-H2) is a quantum solid increasingly utilized in matrix isolation spectroscopy.
• Spectra of embedded molecules in p-H2 exhibit unusually narrow lines, facilitating detailed analysis.
• Previous studies indicate some species can rotate freely within p-H2 matrices.

Purpose of the Study:

• To investigate the rotational and internal dynamics of isolated methanol (CH3OH) within a p-H2 matrix.
• To analyze the impact of the p-H2 host on methanol's internal rotation and nuclear spin symmetry.
• To explore the potential of p-H2 matrix isolation for studying nuclear spin conversion relevant to astrophysics.

Main Methods:

• Matrix isolation spectroscopy of methanol (CH3OH) in a quantum solid para-hydrogen (p-H2) matrix.
• High-resolution spectral analysis of internal rotation-coupled vibrational modes.
• Observation and analysis of spectral splittings related to the E/A torsional doublet.
• Monitoring of nuclear spin symmetry conversion (E to A species) over time.

Main Results:

• The p-H2 matrix significantly inhibits the overall rotation of isolated methanol molecules.
• Internal rotation about the C-O bond in methanol is still permitted within the p-H2 matrix.
• Observed splittings of the E/A torsional doublet in vibrational modes align with gas-phase methanol behavior.
• Slow conversion of methanol's nuclear spin symmetry from species E to species A was detected.

Conclusions:

• Para-hydrogen matrix isolation provides a simplified spectral environment for studying molecular dynamics.
• Methanol retains internal C-O bond rotation in p-H2, with spectral features consistent with gas-phase data.
• The observed nuclear spin conversion offers insights into processes occurring in astrophysical environments.