Interaction of Thermal Electrons with Polarizable and Polar Molecules

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Abstract
Drift velocities w were measured for thermal electron swarms traveling through gases and gas mixtures. The w data are used to calculate average cross sections for momentum transfer, σ's, which are assumed to have a v−1 and a v−2 dependence for nonpolar and polar molecules, respectively. An effort is made to correlate the experimental values of σ with the molecular polarizabilities and/or the molecular dipole moments. The theoretically predicted correlations are discussed and compared with our experiments. Simple theories of long‐range forces agree reasonably well with the experimental data; the agreement between theory and experiment is better when the theory avoids the use of the Born approximation. Various factors proposed to account for the observed differences between the experimental data and the simple theory of short‐range inductive forces are discussed, and the conclusion is drawn that detailed theoretical consideration must be given to each nonpolar molecule before agreement with experiments can be achieved.