The drift velocity of electrons in hydrogen. nitrogen. oxygen. carbon monoxide. carbon dioxide. and air free from water vapour and carbon dioxide. at ambient temperatures (293-296 K) has been measured by the modified Bradbury-Nielsen tirne-of-flight method over the range of the reduced electric field € / S : 0.05 G €/,V c 250 Td. 0.1 c €/l' c 250 Td. 1.0 c E!N c 275 Td. 0.1 c €/h's l50 Td. 0.6 c €1.1; c 250 Td and 0.05 c € .V c 100 Td respectively. The present results are compared with those obtained by other investigators.

The measurements of the drift velocities and characteristic energies of electrons in deuterium are presented. Drift velocities are obtained between 3 and 125 Td by a standard Bradbury-Nielsen technique with a double set of shutters. The characteristic energy for the transverse diffusion was measured by a standard Townsend-Huxley technique to be between 3 and 1000 Td. The drift velocities and characteristic energies are in good agreement with the best available data in the range of overlap and extend the availability of the experimental data to higher E/N. The predictions based on the best available cross section sets do not match the experimental results at higher E/N above the limits of the previously available data.

With the help of the Townsend and Huxley technique the measurement of the ratio of lateral diffusion coefficient to mobility D / p in hydrogen and nitrogen at ambient temperature has been carried out for reduced electric fields 34.7< E/N < 462.7 Td and 2.5 C E/N 6404.6 Td respectively.

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