Rotational Excitation ofH2Oby Cold Electrons

Abstract

Experimental data are presented for the scattering of electrons by H2O between 17 and 250 meV impact energy. These results are used in conjunction with a generally applicable method, based on a quantum defect theory approach to electron-polar molecule collisions, to derive the first set of data for state-to-state rotationally inelastic scattering cross sections based on experimental values.

Low-energy total electron scattering in the methyl halides CH3Cl, CH3Br and CH3I

“…The major reason for the discrepancy is that the Born model omits pure elastic scattering. While there are no data to estimate pure elastic scattering for the present halides, we know however from results for rotationally inelastic scattering in H 2 O [28,29] that pure elastic scattering makes an increasing contribution towards the total cross-section at low energy and may approach 40% of the total below 200 meV. Our results suggest that the contribution of pure elastic scattering is comparable in the methyl halides to that in H 2 O but somewhat less.…”

“…The very high cross-sections found for rotationally inelastic scattering emphasise the importance of polar molecules in determining the electron energy distribution within cool plasmas. An important advance, that is presently being made, is to apply the theory described in [29] to obtain accurate state-to-state rotationally inelastic cross-sections from experimental data for CH 3 Cl and CH 3 Br and elastic scattering cross-sections. This will give an accurate assessment of the relative amount of pure elastic and rotationally inelastic scattering at any energy.…”

Electron and positron collisions with polar molecules: studies with the benchmark water molecule

“…In particular, recent electron collision studies successfully extrapolated measurements to lower angles using calculations based on the Born approximation (Khakoo et al 2008b, Silva et al 2008, leading to the claim (Silva et al 2008) that these new measurements disagree significantly with previous evaluations and as a consequence the results given in the recent tabulation of electron-water cross sections (Itikawa and Mason 2005) should be modified accordingly. Furthermore, Curík et al (2006) have recently made a variety of measurements for ultralow energy collisions which should be the hardest to reproduce theoretically.…”

Energy deposition model based on electron scattering cross section data from water molecules

“…Following the discussion of Ref. [38], some previous experimental results [40][41][42] are also shown in this figure for comparison. A complementary discussion of data on electron scattering from water molecules can be found in Refs.…”

“…The origin of this discrepancy has been discussed previously [38] and it seems to be connected to the target rotational distribution and the acceptance angle of detectors used in the experiments. Since this point has not been completely clarify at the moment, we will take the experimental results of [40] and [42] as recommendable low energy data for our model.…”