7%~ mobilities of thermal electrons in tr-nlkanc vapors decrease with increasing static polarizability and the mcasurad scattering cross sections compxc we11 with the geometric cross sections. Evidence is provided for tile cxistcnce of ;I Ramsarer-Townsend minimum in Cz116 and C3118. 1. htmduction 'hc rr-aIkiinc molecules possess only CJ bonds, have little or no permanent electric dipole morrmts and on the basis of their structure it may be possible to investigate the role of the static polarizabilily (Y on the mction of thermal clcctrons through these organic Y~PCIIS. The present study SIWWS that the mobilities of thermal electrons in the n-alkane vapors decrease with increasing Q' and that the mcasured scattering cross sections are comparable to the ,oeometric cross sections. A comparison of thermal elec:ron mobilities in a Ilumber of substaxes rcvealed that thermal electrons are more mobile in N.
alkrrncs than in other gsseous media of comparable cy. These latter studies indicated also that at %?98 K the mobility of thermal electrons is the largest for Ne and that at 1 torr pressure the mobility is ==108 cm2 s-' V-* when (3~ + 0. Furthcrmorc, it was fcund that o Ramsaucr--Townsend-type behavior is exhibited by C2l-l~ and C3H8 with the cross section minimum shifted to lower energies than for Cl-l,. The minimum f& CHq is shifted to lower energies (closer to thermal) with increasing density of the medium.