Excess electrons in dense hydrocarbon gases: The effect of molecular shape on electron mobilities.

测量了超临界n-(n-B)、异丁烷(I-B)、n-(n-P)、异-(i-P)和新戊烷(NEOP)中过剩电子的迁移率和导电态能Vo随密度N的变化，随着N的增加，所有碳氢化合物中的密度归一化迁移率&lt；Mu&gt；N在低于各自临界密度的密度处经历最小值，然后增大到最大。当N=0时，VO值从零开始减小，然后随N的升高而增大。升高温度使所有碳氢化合物的最大值向低N方向移动，但最大值仅在n-B和n-P中向低N方向移动。在其他更对称的碳氢化合物中，极大值的轨迹与温度无关。利用由声速估算的结构因子，Cohen-Lekner模型很好地再现了包含温度依赖性的n-B和n-P中的极小值。在I-B、I-P和NEOP中，模型预测在比观测密度更高的密度下出现极小值，并且必须考虑散射截面大小随N的变化。在这些碳氢化合物中，观察到Vo极小值和&lt；Mu&gt；N极大值之间的对应关系，这表明形变势的极小值是极大值出现的原因。直链碳氢化合物中的最大值是由于非对称分子的配位数和取向的波动密度越高，从准自由电子态到定域电子态的转变所引起的重要性的增加。介电介质中过剩电子研究的下一步是研究更高密度区域(高压下)中的u和Vo行为，目的是收集有关局域态的性质的信息。

The mobility <mu> and the conducting state energy Vo of excess electrons in supercritical n-(n-B), isobutane(i-B), n-(n-P), iso-(i-P) and neopentane(neoP) were measured as a function of density N, With increase in N,the density-normalized mobility <mu> N in all hydrocarbons studied goes through a minimum at a density below the respective critical density, and then increases to a maximum. Vo values initially decrease from zero at N=0, and then increase wth N. Raising temperature causes <mu> N minima to shift toward lower N in all hydrocarbons, but the maxima shift to lower N only in n-B and in n-P. In other more symmetrical hydrocarbons the loci of maxima are independent of temperature. The minima in n-B and n-P including temperature dependence is adequately reproduced by the Cohen-Lekner model with the use of the structure factor estimated from the speed of sound. In i-B,i-P and neoP the model predicts the occurrence of the minima at a higher densities than are observed, and changes in the magnitude of scattering cross section with N have to be invoked, In these hydrocarbons the correspondence of Vo minima and <mu> N maxima is observed, which indicates that the minima of the deformation potentials are the cause for the appearance of the maxima. The maxima in the straight-chain hydrocarbons are due to the transition from the quasifree to the localized electron states caused by the increased importance at higher densities of fluctuations in coordination numbers and orientations of unsymmetrical molecules. The next step of the study of excess electrons in dielectric media is to investigate <mu> and Vo behavior in a still higher density region (under high pressure) with the aim to gather information concerning the nature of localized states.