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.

By means of the Blevin - Hasan version of the Bradbury - Nielsen technique and Townsend - Huxley method, the drift velocity W, characteristic energy and the parameter have been determined at ambient temperature for reduced electric fields Td, Td and Td, respectively. The present results have been compared with experimental and theoretical ones of other investigators.

Measurements of the ratio of the transverse diffusion coefficient to the mobility D T /µ (or the characteristic energy eD T /µ) were performed for the reduced electric field (E/N) from 12 Td to 300 Td (1 Td = 10 −21 V m 2 ). The ratio of longitudinal diffusion coefficient to mobility (D L /µ) is determined from the fits of the appropriate current ratios obtained from a Townsend-Huxley experiment as a function of pressure and geometry for a fixed E/N. The results cover a range of moderate E/N and bridge the gap between the two sets of data available in the literature, while covering the range of energies corresponding to the vibrational excitation.

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.