Temperature Dependence of Rotational Collision Numbers from Thermal Transpiration

The temperature dependence of the rotational collision numbers for O2, N2, CO, and CO2 was investigated in the range 475–676°K by the thermal transpiration technique with the use of a novel apparatus design. In all cases the collision number was found to increase with temperature. For O2 and N2, where some comparison with theory is possible, the experimental rate of increase with temperature was found to be faster than the predicted behavior. The results for CO and CO2 are in general agreement with other transpiration measurements and with acoustic absorption results which were obtained at lower temperatures.