Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases.,The Journal of Physical Chemistry A

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Infrared Spectroscopic Study of Solid Methane: Nuclear Spin Conversion of Stable and Metastable Phases.
The Journal of Physical Chemistry A ( IF 2.7 ) Pub Date : 2020-01-13 , DOI: 10.1021/acs.jpca.9b10643
Shahnewaz M Emtiaz ₁ , Francis Toriello ₁ , Jiao He ₂ , Gianfranco Vidali ₁

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Infrared spectroscopy was employed to study thin films of solid methane at low temperatures. We report new measurements of temporal changes of infrared spectra of methane ice in the ν3 and ν4 bands due to nuclear spin conversion upon rapid cooling from 30 to 6.0-11.0 K. The relaxation rates of the nuclear spin were found to be a function of temperature. The activation energy associated with the relaxation has been determined over an extended temperature range. We also found a new metastable phase of methane ice upon deposition at T < 7 K. After the deposition at 6 K and annealed to a higher temperature, a phase transition from the metastable phase to a stable crystalline phase takes place. We found that the relaxation has different activation energies below and above 8.5 K. From a quantitative analysis of the ν3 and ν4 IR bands, we suggest that the metastable phase is a crystalline phase with a degree of orientational disorder between the two known stable solid phases.

中文翻译：

固体甲烷的红外光谱研究：稳定相和亚稳相的核自旋转化。

红外光谱法用于研究低温下的固体甲烷薄膜。我们报告了由于从30到6.0-11.0 K的快速冷却后核自旋转换而引起的ν3和ν4波段甲烷冰的红外光谱随时间变化的新测量。发现核自旋的弛豫率是温度的函数。与弛豫相关的活化能已经在扩展的温度范围内确定。我们还发现了在T <7 K沉积时甲烷冰的新的亚稳相。在6 K下沉积并退火至更高的温度后，发生了从亚稳相到稳定结晶相的相变。我们发现，在8.5 K以下和以上，弛豫具有不同的激活能。通过对ν3和ν4IR波段的定量分析，

更新日期：2020-01-14

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