Cooling rate of an electron gas by polar molecules

The cooling rate of electron gas was considered from the standpoint of the rotational and vibrational processes of polar molecules. The function of electron velocity distribution was assumed to be Maxwellian, while the rotational and vibrational level populations were assumed to obey Boltzmann distribution. By using the cross-sections obtained from Born approximation for the dipole transition between rotational states, the analytical expression for the cooling rate of symmetric-top molecules under rotational excitation was derived with the assumption that the statistical weights which oscillate periodically for the rotational quantum numbers are neglected. Similar expressions for diatomic molecules and asymmetric-top molecules were also derived. Calculation was made on the rate of electron energy loss for several asymmetric-top molecules. An example of the results for H2O is shown in a figure. The expression for the vibrational excitation was also derived by the harmonic oscillator approximation for molecular vibration. (Aoki, K.)