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Exploring the Arginine Methylome by Nuclear Magnetic Resonance Spectroscopy
Published on: December 16, 2021
Rotation of methyl radicals in a solid argon matrix
Evgeny Popov1, Toni Kiljunen, Henrik Kunttu
1Department of Chemistry, University of Jyväskylä, P.O. Box 35, Jyväskylä FIN-40014, Finland.
The Journal of Chemical Physics
|April 14, 2007
Summary
Electron spin resonance (ESR) studies reveal methyl radical (CH3) rotation in solid argon. Temperature influences ground and excited states, showing distinct spin behaviors and revealing a 60 cm-1 rotational barrier.
Area of Science:
- Physical Chemistry
- Solid-State Physics
- Spectroscopy
Background:
- Methyl radicals (CH3) are fundamental molecular species.
- Understanding molecular rotation in solid matrices is key to condensed matter physics.
- Solid argon provides a well-defined environment for studying radical dynamics.
Purpose of the Study:
- To investigate the rotational dynamics of methyl radicals in a solid argon matrix.
- To characterize the ground and excited rotational states of CH3 radicals.
- To determine the rotational energy levels and potential barriers using ESR.
Main Methods:
- Electron spin resonance (ESR) spectroscopy was employed.
- Methyl radicals were generated by plasma dissociation of methane.
- Measurements were conducted in a solid argon matrix at temperatures ranging from 14-35 K.
- Numerical fitting procedures were used to analyze spectral data.
Main Results:
- ESR spectra showed axial symmetry at low temperatures, attributed to ground state CH3 radicals (I=3/2).
- Observed hyperfine and g-value anisotropy for the first time in Ar, with values (Aparallel-Aperpendicular) = -0.01 mT and g-value anisotropy = 2.5x10(-5).
- Temperature elevation led to reversible appearance of excited state contributions (I=1/2), with ground and excited states separated by 11.2 cm-1.
- A crystal field model yielded a parameter varepsilon4 = -200 cm-1, indicating a 60 cm-1 effective potential barrier for rotation.
Conclusions:
- Methyl radical rotation in solid argon involves free rotation about the C3 axis and thermally activated C2 rotations above 15 K.
- Ground and excited rotational states exhibit distinct spin-lattice coupling.
- The study provides quantitative insights into hindered rotation and energy barriers in solid matrices.
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