Rotational excitation of N₂, CO and H₂O by low-energy electron collisions

Abstract

Absolute total and differential rotational and rotational-vibrational cross sections have been measured for N2 (weak quadrupole), CO (weak dipole), and H2O (strong dipole). In the beam experiments, the range of collision energies of the electrons was chosen between 0.5 and 6 eV, and the range of scattering angles from 15 to 105 degrees was covered. The overall energy inhomogeneity of the electron spectrometer was between 10 and 18 meV FWHM, depending on the experiment. Direct and resonant rotational excitation has been measured. In the case of N2 the rotational branches with Delta J=0, +or-2, +or-4 have been fitted to energy-loss spectra and for each branch a cross section is given. The authors have proceeded similarly in the case of CO (for dipole excitation Delta J=0, +or-1, for excitation via the 2 Pi resonance Delta J=0, +or-1, ..., +or-4) and in the case of H2O ( Delta J=0, +or-1). For N2 and CO the results are compared with calculated angular dependences. Finally, the cross sections are listed according to the different types of interaction potentials and interaction mechanisms.

Electron collisions with CO: Elastic and vibrational excitation cross sections

“…The difference becomes larger below about 30 • at 1.94 eV. The data of Jung et al [11] (open triangles in Fig. 10) agrees very well with the present data in shape, but are slightly higher in magnitude.…”

“…Rotational excitation is, particularly in the resonance region, strong [11] and leads to a substantial broadening of the energy-loss bands. Consequently, care had to be taken to derive all cross sections from the areas under the energy-loss bands and not from their heights.…”

“…Tanaka et al [9] measured the elastic cross sections in the range 15 • -130 • , later used by Chutjian and Tanaka to derive the absolute inelastic cross sections [10]. Jung et al [11] performed a high-resolution (∼10 meV) experiment and obtained absolute differential cross sections for pure rotational and for ro-vibrational (v = 1) excitation. Sums over all rotational transitions can be compared to the present data.…”

Ramsauer-Townsend minimum in methane — modified effective range analysis

“…Shallow "valleys" in total cross sections are visible in H 2 O and NH 3 [11], but the possible presence of an R-T minimum is masked by strong rotational excitation, see analysis in [8]. Excluding rotations from experimental vibrationally elastic cross sections [12] would yield an R-T minimum in elastic cross section in H 2 O of about 2Å 2 at 2 eV but both the experiment and the analysis are tedious and can lead to serious errors, see [8].…”

A theoretical study on e--CO elastic collision using the configuration interaction method to describe the target

“…For instance, rotational excitations cross sections were studied by Sohn et al [2] and Gote and Ehrhardt [3], and vibrational excitation processes by Chutjian and Tanaka [4], Tronc et al [5] and Gibson et al [6]. Cross sections for elastic, vibrational excitations and electronic excitations leading to some lying states of CO were reported by Middleton et al [7]; elastic differential cross sections (DCS) measurements have also been performed by Nickel et al [8] and elastic and vibrational cross sections by Jung et al [9]. In addition a substantial number of measurements of the total (elastic + inelastic) cross sections has been presented in the literature [10][11][12].…”