Electron impact dissociative excitation of O₂: 2. Absolute emission cross sections of the OI(130.4 nm) and OI(135.6 nm) lines

Abstract

[1] In this work, we report the OI(135.6 nm) absolute emission cross section resulting from the long-lived (180 ms) OI( 5 S ! 3 P) transition from dissociative excitation of O 2 . From the ratio of the integrated intensities of the OI(135.6 nm) and OI(130.4 nm) features and from the absolute emission cross section for the OI(130.4 nm) emission feature from electron impact dissociative excitation of O 2 at 100 eV, the absolute emission cross section for the OI(135.6 nm) feature was determined to be 6.4 Â 10 À18 cm 2 at 100 eV. Electron impactinduced optical excitation functions for optically allowed transitions at 115.2 nm and 130.4 nm and for an optically forbidden transition at 135.6 nm were also obtained over the electron impact energy range 0-600 eV. The OI(135.6 nm) emission cross section was measured in the laboratory utilizing a large collision chamber (1.5 m in diameter). Electrons were produced with an electrostatically focusing gun with a large focal length (50 cm). The OI(130.4 nm, 135.6 nm) excitation functions were put on an absolute scale as described in the text, and the OI(135.6 nm)/OI(130.4 nm) ratio was determined for the entire energy range (0-600 eV). The atomic O UV emission cross sections from dissociative excitation of O 2 can be used to model the recent Hubble Space Telescope observations of OI(130.4 nm) and OI(135.6 nm) intensities from Ganymede [Feldman et al., 2000] and Europa [Hall et al., 1995[Hall et al., , 1998].

Polar cap arcs from the magnetosphere to the ionosphere: kinetic modelling and observations by Cluster and TIMED

“…O + -O − neutralization may also play a role (around 5 % of the total emission), especially in the mid-latitude ionosphere (Meier, 1991;Dymond et al, 2000) and at low altitudes. These two last mechanisms as well as cascades from 5 P upper states (Kanik et al, 2003) will not be considered here as a lower estimate is sought. Processes (a) and (b) contribute to more than 85 % of the total brightness (Strickland and Anderson, 1983;Strickland et al, 1993) and processes (c) and (d) to around 10 % or less (Dymond et al, 2000, and this study).…”

“…The most recent cross-sections for processes (a) and (b) used in the computation are Laher and Gilmore (1990) and Kanik et al (2003), respectively. The recommendation of Laher and Gilmore (1990) for process (a), deduced from calculations, is in qualitative agreement with the laboratory measurements reported by Stone and Zipf (1974), later corrected by Zipf and Erdman (1985) and Doering and Gulcicek (1989); the uncertainty reaches 50 %.…”

Orbital apocenter is not a sufficient condition for HST/STIS detection of Europa’s water vapor aurora

“…Model aurora images are generated by calculating the expected morphology from an electron-excited atmosphere consisting of O 2 , O, and H 2 O based on the available cross sections for electron impact (dissociative) excitation of the neutrals (38)(39)(40)(41). To be consistent with previous estimations we further apply the constant electron parameters used in previous aurora studies (5)(6)(7)14): a total electron density of 40 cm −3 , a thermal electron population with a temperature of T e = 20 eV, and a suprathermal population with T e = 250 eV and a 2% mixing ratio.…”

Laboratory studies of UV emissions from proton impact on N2: The Lyman-Birge-Hopfield band system for aurora analysis

“…Absolute electron impact emission cross-section studies for metastable species rely on a LBH emission glow model to extrapolate signal outside the FOV. Two metastable species have been studied by this method in our laboratory: the LBH band system (AS85) from direct excitation of N 2 and the 135.6 nm atomic O 5 S emission [Kanik et al, 2003] from dissociative excitation of O 2 . The lifetime of the a 1 P g state has been, until now, uncertain, with experiments and theory reporting values that typically range from 54 ms to 170 ms.…”