Vibrational and rotational cooling of electrons by water vapor

Abstract

The cooling of electrons by vibrational and rotational excitation of water molecules plays an important role in the thermal balance of electrons in cometary ionospheres. The energy loss function for rotational excitation and de-excitation of Hz0 by electron impact is calculated theoretically. The rotational cooling rate is calculated using this loss function for a wide range of electron and neutral temperatures. The vibrational cooling rate is calculated using measured values of electron impact vibrational excitation cross sections. Analytical formulae are provided for some of the cooling rates. The interaction of ions with H,O molecules is also discussed and a formula is suggested for the momentum transfer collision frequency.

Understanding measured water rotational temperatures and column densities in the very innermost coma of Comet 73P/Schwassmann–Wachmann 3 B

“…This phenomenon locally dominates even heating by photoionization (Häberli et al, 1995(Häberli et al, , 1996. Cravens and Körösmezey (1986) studied the effect of collisions between electrons and water molecules on the vibrational and rotational temperature of water. They calculated theoretically the energy loss function for rotational excitation and de-excitation of water molecules by electron impact using cross sections for electron impact rotational transitions derived with the first Born approximation.…”

Ion acoustic waves at comet 67P/Churyumov-Gerasimenko

“…2, and has thus travelled through a region with lower neutral density. The ion-neutral collision cross section is proportional to E −1/2 (Cravens & Korosmezey 1986). Once they have gained some energy, the beam ions would thus be less affected by collisions than the bulk of the locally generated ions that start out at the same velocity as the neutrals.…”

The chemistry of C3and C2in cometary comae

“…Furthermore, we included an energy source term describing the energy exchange caused by elastic collisions of electrons with ions, taken from Draine (1980), in addition to another energy source term that takes inelastic collisions of electrons with water into account. To achieve this, we incorporated the analytic parametrisation of Cravens & Korosmezey (1986) for the rotational and vibrational excitation of the water molecule in our model. As described in Sect.…”