Nuclear spin conversion of methane in pure and rare-gas mixed crystals
Nuclear spin conversion of methane in pure and rare-gas mixed crystals
复制标题
纯气体和稀有气体混合晶体中甲烷的核自旋转化
DOI：
10.1007/bf01315649
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发表时间：
1992
期刊：
影响因子：
--
通讯作者：
R. Scherm
中科院分区：
文献类型：
--
作者：
S. Grieger;H. Friedrich;B. Asmussen;K. Guckelsberger;D. Nettling;W. Press;R. Scherm
用中子散射的方法观察到了自旋物种转化。通过测量非弹性中子谱的详细平衡因子随时间的变化，研究了稀有气体晶体中的甲烷基质。结果表明，在2~5K温度范围内，转化率随温度的变化比单声子过程预测的要强。通常，转换时间在该温度区域内为小时的数量级。矩阵的影响可以用耦合声子态密度来很好地描述。通过测量甲烷晶体的中子总散射截面随时间的变化关系，对纯甲烷和掺氪甲烷晶体进行了研究。对于纯甲烷，转化率随温度的变化表现为自由旋转体和有序分子两个区域。在5K以下，用单声子过程描述，在5K以上用阿累尼乌斯定律描述。由于取向无序，导致能级间距发生变化，从而导致了氪原子的点迹，从而提高了速率。
Spin species conversion has been observed by means of neutron scattering. Methane, matrixisolated in rare-gas crystals has been investigated by measuring the time dependence of the detailed balance factor of inelastic neutron spectra. The temperature dependence of conversion rates in the interval between 2 and 5 K turns out to be stronger than predicted by a single phonon process. In general, conversion times are of the order of hours in this temperature region. The influence of the matrix is well described by a coupled phonon density of states. Crystals of pure and krypton doped methane have been examined by measuring the time dependence of the total neutron scattering cross section. For pure methane, the temperature dependence of the conversion rates shows two regimes for both free rotator and ordered molecules. Below 5 K, the behavior is described by a single phonon process and above by an Arrhenius law. Rates are enhanced by krypton dotation, which is explained by changed level spacings due to orientational disorder.