Excess electron mobility in liquid Kr-CH/sub 4/ mixtures

The electric field dependence of the mobility of excess electrons has been measured in mixtures of liquid Kr doped with CH/sub 4/ in several concentrations up to 10%, for T=125 K and up to E=1 MV/m. It appears that CH/sub 4/ is less effective than rare gas impurities to thermalize electrons at high fields. A concentration-dependent threshold field has been found at which electrons can excite the first vibrational level of the methane molecule.