The drift velocity of electrons in water vapour at low values of E/N

The drift velocity of electrons in water vapour at 294 K has been measured over the E/N range 1.4 to 40 Td with an error estimated to be 35 Td. The present data show that μN decreases monotonically with decreasing E/N at low E/N values as observed by Wilson at al. (1975) and does not become independent of E/N as indicated by Lowke and Rees (1963). The present values, although lower than those of Lowke and Rees, lie within the combined error limits, except for values below 2 Td. The present data suggest that the momentum transfer cross section at low energies is approximately 10% larger than that obtaineds by Pack at al. (1962) from their drift velocity measurements