This work presents swarm parameters of electrons (the bulk drift velocity, the bulk longitudinal component of the diffusion tensor, and the effective ionization frequency) in C$_2$H$_n$, with $n =$ 2, 4 and 6, measured in a scanning drift tube apparatus under time-of-flight conditions over a wide range of the reduced electric field, 1 Td $\leq\,E/N\,\leq$ 1790 Td (1 Td = $10^{-21}$ Vm$^2$). The effective steady-state Townsend ionization coefficient is also derived from the experimental data. A kinetic simulation of the experimental drift cell allows estimating the uncertainties introduced in the data acquisition procedure and provides a correction factor to each of the measured swarm parameters. These parameters are compared to results of previous experimental studies, as well as to results of various kinetic swarm calculations: solutions of the electron Boltzmann equation under different approximations (multiterm and density gradient expansions) and Monte Carlo simulations. The experimental data are consistent with most of the swarm parameters obtained in earlier studies. In the case of C$_2$H$_2$, the swarm calculations show that the thermally excited vibrational population should not be neglected, in particular, in the fitting of cross sections to swarm results.

中文翻译：

---

C ₂ H ₂、C ₂ H ₄和C ₂ H _{6 中的}电子群参数：测量和动力学计算

这项工作展示了 C$_2$H$_n$ 中电子的群参数（体漂移速度、扩散张量的体纵向分量和有效电离频率），其中 $n =$2、4 和 6，测量在飞行时间条件下的扫描漂移管装置中，在较宽的减小电场范围内，1 Td $\leq\,E/N\,\leq$ 1790 Td (1 Td = $10^{-21} $ Vm$^2$）。有效稳态汤森电离系数也来自实验数据。实验漂移单元的动力学模拟允许估计数据采集过程中引入的不确定性，并为每个测量的群参数提供校正因子。这些参数与先前实验研究的结果以及各种动力学群计算的结果进行了比较：电子玻尔兹曼方程在不同近似（多项式和密度梯度扩展）和蒙特卡罗模拟下的解。实验数据与早期研究中获得的大多数群参数一致。在 C$_2$H$_2$ 的情况下，群计算表明不应忽略热激发振动群，特别是在将横截面拟合到群结果时。