“…In a recent theoretical investigation Bardsley (1968) concludes that a, should vary approximately as for ions in their ground electronic and vibrational state. This is in accordance with some experimental findings, notably for 0,' (Mentzoni 1965) and Ne,' (Kasner 1968 ;Chen 1969), and as will be seen in the following for CO' . On the other hand, the temperature variation of a, as determined in nitrogen (Hagen 1968;Kasner 1968;Mentzoni 1963 ;Bialecke and Dougal1958), oxygen (Kasner and Biondi 1968), nitric oxide (Gunton and Shaw 1965), helium (Chen et al 196 1 ;Chen 1969), and argon (Fox and Hobson 1966;Chen 1969) can be expressed as 0 5 y 5 1.5 when the data are fitted with a simple power law, TePY.…”