One-electron capture in collisions of 6 - 100 keV protons with oxygen atoms

Abstract

A crossed-beam technique incorporating time-of-flight analysis and coincidence counting of the collision products has been used to study one-electron capture by 6 - 100 keV protons in collisions with oxygen atoms. In these measurements, ground-state oxygen atoms were provided by an iridium tube furnace dissociation source. The measurements extend the energy range of previous experiments and, for the first time, provide separate cross sections for the simple charge transfer process (which is dominated by accidentally resonant one-electron capture) and for the transfer ionization process leading to formation. The present cross sections were obtained using a technique and normalization procedure different from all previous measurements. In particular, our measured values of are in good accord with previous 0.04 - 10 keV data by Stebbings et al based on a modulated crossed-beam technique but at variance with the considerably smaller values in the range 2.5 - 25 keV obtained by Williams et al using a furnace target method. While our values of decrease with increasing energy over the range considered, transfer ionization cross sections pass through a peak value at 34 keV where this process accounts for about 9% of the total one-electron capture cross section rising to 17.5% at 100 keV.

Cross sections for electron capture and loss by H+ and H impact on O and O2

“…With the exception of the Williams et al [] data, the other results shown in Figure a are in very reasonable accord, considering the difficulty of working with reactive O‐atoms as a target gas and the use of a large variety of absolute‐calibration techniques. Our results appear to merge smoothly with the higher‐H + ‐energy measurements of Thompson et al [] but do appear to be slightly larger than the others shown at the lower H + energies. This comes about in part from our slightly higher σ A /σ M ratios (see Figure a) but mostly from the fact that the σ M measurements of Koopman [] lie above those reported by Lindsay et al [], Stebbings et al [], or Stier and Barnett [].…”

Charge transfer in collisions of O+ with H and H+ with O

“…3 Schryber (1967) [stars], Toburen et al (1968) [open left triangles], Cocke et al (1977) [open squares], Williams et al (1984) [filled diamonds], Thompson et al (1996) [open circles]. Previous theory: Hamre et al (1999) [thin solid line], Lin et al (1978) [thin long dashed line], Tan & Lee (1981) [thin dot-dash line], Miraglia (1984) [thin dot-dash line], Saha et al (1985) [thin solid line] of the fine-structure cross sections agree between 0.1 and 0.5 eV/u, but again diverge for lower energies.…”

“…Figure 4 shows reaction (2) cross sections for energies greater than 100 eV/u. The current CTMC and CDW calculations (which include the sum of capture from the O(1s), O(2s), and O(2p) subshells computed using the independent electron model) are compared with the experiments of Stier & Barnett (1956), de Heer et al (1966, Schryber (1967), Toburen et al (1968), Williams et al (1984), and Thompson et al (1996), and the calculations of Tan & Lee (1981), and the atomic-orbital close-coupling (AOCC) results of Hamre et al (1999). Additionally, the K-shell capture (i.e., removal of an O(1s) electron) measurements of Cocke et al (1977) are compared to the theoretical calculations of Lin et al (1978), Miraglia et al (1984), and Saha et al (1985).…”

Energetic ion characteristics and neutral gas interactions in Jupiter's magnetosphere

“…By combining estimates of sputtering products from Europa with subsequent redistribution interactions, Schreier et al [1993] estimate the following density distribution of neutrals (their “case A”): (H: 13.6 cm −3 ), (H 2 : 0.4), (O: 5), (O 2 : 1.5), (OH, 1.3), and (H 2 O: 1.3). Using the 50 to 80 keV H + mean cross‐section values σ 1 = 0.6 × 10 −16 cm 2 for H + on H [ Barnett et al , 1990], σ 2 = 1.14 × 10 −16 cm 2 for H + on H 2 [ Rudd et al , 1983], σ 3 = 1.9 × 10 −16 cm 2 for H + on O [ Thompson et al , 1996], σ 4 = 2.1 × 10 −16 cm 2 for H + on O 2 [ Rudd et al , 1983], and σ ij = ( i σ 1 + j σ 3 ) for H + on H i O j (for those unspecified neutral species), one obtains a density‐weighted mean cross section of σ m = 1.24 × 10 −16 cm 2 . With this value for σ m our estimate for the total gas content of the Europa gas torus is N g = (0.6 ± 0.25) × 10 34 atoms plus molecules, with the error range not including uncertainties in the cold gas composition.…”