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Nuclear spin conversion of methane in solid parahydrogen.

Yuki Miyamoto¹, Mizuho Fushitani, Daisuke Ando

¹Division of Chemistry, Graduate School of Science, Kyoto University, Kyoto, Japan.

The Journal of Chemical Physics

|March 26, 2008

Summary

Nuclear spin conversion rates for methane (CH4) and deuterated methane (CD4) in solid parahydrogen were measured. CD4 converts 2-100 times faster than CH4 due to different interactions and phonon processes.

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Area of Science:

Quantum Chemistry
Spectroscopy
Solid-State Physics

Background:

Nuclear spin conversion is a fundamental process in molecular physics.
Understanding these conversions in confined environments like solid parahydrogen is crucial for molecular dynamics studies.

Purpose of the Study:

To investigate and compare the nuclear spin conversion rates of methane (CH4) and deuterated methane (CD4) isolated in solid parahydrogen.
To elucidate the mechanisms and temperature dependence of these conversion processes.

Main Methods:

High-resolution Fourier transform infrared (FTIR) spectroscopy was employed.
Temporal changes in rovibrational absorption spectra were analyzed to determine conversion rates.

Main Results:

Nuclear spin conversion rates were determined for CH4 and CD4 between 1 and 6 K.
CD4 exhibited conversion rates 2-100 times faster than CH4.
Conversion mechanisms were attributed to nuclear spin-nuclear spin interaction for CH4 and quadrupole interaction for CD4.
Temperature dependence revealed dominant one-phonon processes at low temperatures and two-phonon processes at higher temperatures.

Conclusions:

The study provides insights into the distinct nuclear spin conversion dynamics of CH4 and CD4 in solid parahydrogen.
The findings highlight the influence of isotopic substitution and intermolecular interactions on conversion rates and mechanisms.
Temperature-dependent phonon processes play a significant role in driving nuclear spin conversion in these systems.