Absorption Cross Sections of O2(a1Δg) and O2(X3Σg−) in the Region from 1087 to 1700 Å

Ogawa, Soichi; Ogawa, Masaru

doi:10.1139/p75-236

Cited by 120 publications

(55 citation statements)

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“…The cross-section of the primary atmospheric constituent, O 2 , reaches the highest values at the observed FUV wavelengths near 1244.4 and 1205.4 Å, and at the SchumannRunge continuum above ∼1300 Å (Ogawa & Ogawa 1975;Lu et al 2010). At 1216 Å (Lyα) the cross-section assumes a lower value of ∼1×10 −20 cm 2 (Ogawa 1968 (Hall et al 1998;Roth et al 2016), which corresponds to a maximum line-of-sight column density of , or a transmittance of >99.9%.…”

Section: Estimation Of the Optical Depth And Emission Contributionsmentioning

confidence: 97%

DETECTION OF A HYDROGEN CORONA IN HST Lyα IMAGES OF EUROPA IN TRANSIT OF JUPITER

Roth

Retherford

Ivchenko

et al. 2017

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We report far-ultraviolet observations of Europa in transit of Jupiter obtained with the Space Telescope Imaging Spectrograph of the Hubble Space Telescope on six occasions between 2014 December and 2015 March. Absorption of Jupiter's bright hydrogen Lyα dayglow is detected in a region several moon radii above the limb in all observations. The observed extended absorption provides the first detection of an atomic hydrogen corona around Europa. Molecular constituents in Europa's global sputtered atmosphere are shown to be optically thin to Lyα. The observations are consistent with a radially escaping H corona with maximum densities at the surface in the range of (1.5-2.2)×10 3 cm −3 , confirming the abundances predicted by Monte Carlo simulations. In addition, we search for anomalies around the limb of Europa from absorption by localized high H 2 O abundances from active plumes. No significant local absorption features are detected. We find that an H 2 O plume with line-of-sight column density in the order of 10 16 cm −2 , as inferred by Roth et al. would not be detectable based on the statistical fluctuations of the transit measurements, and hence is not excluded or further constrained. The presence of plumes with line-of-sight column densities of >2×10 17 cm −2 can be excluded at a 3-σ level during five of our six observations.

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Section: Estimation Of the Optical Depth And Emission Contributionsmentioning

confidence: 97%

DETECTION OF A HYDROGEN CORONA IN HST Lyα IMAGES OF EUROPA IN TRANSIT OF JUPITER

Roth

Retherford

Ivchenko

et al. 2017

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“…Photoabsorption cross sections are most frequently recorded directly, by observing the transmission of an ultraviolet continuum through a gas sample, with radiation generated by discharge lamps (e.g., Ogawa & Ogawa 1975;Dehmer & Chupka 1976) or synchrotrons (e.g., Yoshino et al 1996;Cheng et al 2011), and dispersed by diffraction gratings or interferometry (Yoshino et al 2006). Laser-generated ultraviolet radiation is sometimes used in photoabsorption experiments and provides the highest spectral resolution (Gao et al 2013;Niu et al 2014), but generally cannot be tuned over a large wavelength range or provide controllable intensity.…”

Section: Experimental Cross Sectionsmentioning

confidence: 99%

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Heays

Bosman

Dishoeck

2017

A&A

442

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A new collection of photodissociation and photoionisation cross sections for 102 atoms and molecules of astrochemical interest has been assembled, along with a brief review of the basic physical processes involved. These have been used to calculate dissociation and ionisation rates, with uncertainties, in a standard ultraviolet interstellar radiation field (ISRF) and for other wavelength-dependent radiation fields, including cool stellar and solar radiation, Lyman-α dominated radiation, and a cosmic-ray induced ultraviolet flux. The new ISRF rates generally agree within 30% with our previous compilations, with a few notable exceptions. Comparison with other databases such as PHIDRATES is made. The reduction of rates in shielded regions was calculated as a function of dust, molecular and atomic hydrogen, atomic C, and self-shielding column densities. The relative importance of these shielding types depends on the atom or molecule in question and the assumed dust optical properties. All of the new data are publicly available from the Leiden photodissociation and ionisation database. Sensitivity of the calculated rates to variation of temperature and isotope, and uncertainties in measured or calculated cross sections, are tested and discussed. Tests were conducted on the new rates with an interstellar-cloud chemical model, and find general agreement (within a factor of two) in abundances obtained with the previous iteration of the Leiden database assuming an ISRF, and order-of-magnitude variations assuming various kinds of stellar radiation. The newly parameterised dust-shielding factors makes a factor-of-two difference to many atomic and molecular abundances relative to parameters currently in the UDfA and KIDA astrochemical reaction databases. The newly-calculated cosmic-ray induced photodissociation and ionisation rates differ from current standard values up to a factor of 5. Under high temperature and cosmic-ray-flux conditions the new rates alter the equilibrium abundances of abundant dark cloud abundances by up to a factor of two. The partial cross sections for H 2 O and NH 3 photodissociation forming OH, O, NH 2 and NH are also evaluated and lead to radiation-field-dependent branching ratios.

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“…The f-scaling process has the effect of replacing the wave functions used for ICS Born with accurate wave functions. We note that the ICS Born for the SR continuum were calculated from the experimental GOS of Xu et al, 25 and accurate OOS were used from the work of Chan et al 43 On the other hand, the ICS Born for the LB, and SB were calculated from the theoretical work of Li et al, 10 while the required accurate OOSs were used from Ogawa and Ogawa 44 and Lewis et al, 45 respectively. In addition the BE-scaled Born cross sections (ICS BE ) are given by This scaling corrects the well known deficiency of the Born approximation at low E 0 without losing its established validity at high E 0 (Ref.…”

Section: Bef-scaling Detailsmentioning

confidence: 99%

Electron excitation of the Schumann–Runge continuum, longest band, and second band electronic states in O2

Suzuki

Kato

Ohkawa

et al. 2011

The Journal of Chemical Physics

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We report measurements of differential and integral cross sections for electron excitation of the Schumann–Runge continuum, longest band, and second band electronic states in molecular oxygen. The energy range of the present study is 15–200 eV, with the angular range of the differential cross section (DCS) measurements from 2 to 130°. A generalized oscillator strength analysis is then employed in order to derive integral cross sections (ICSs) from the corresponding DCSs, and these ICSs are compared with relevant energy and oscillator strength scaled Born cross section (BEf-scaling [Y.-K. Kim, J. Chem. Phys. 126, 064305 (2007)]) results determined as a part of this investigation. Interestingly, while the present Schumann–Runge continuum and second band ICSs were in reasonable agreement with the respective BEf-scaling results, agreement for the longest band was poor below 100 eV with a possible reason for this apparently anomalous behavior being canvassed here. Finally, where possible all present data are compared with the results from earlier measurements and calculations with the level of agreement found being very good in some cases and marginal in others.

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Absorption Cross Sections of O₂(a¹Δ_g) and O₂(X³Σ_g⁻) in the Region from 1087 to 1700 Å

Cited by 120 publications

References 0 publications

DETECTION OF A HYDROGEN CORONA IN HST Lyα IMAGES OF EUROPA IN TRANSIT OF JUPITER

DETECTION OF A HYDROGEN CORONA IN HST Lyα IMAGES OF EUROPA IN TRANSIT OF JUPITER

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Electron excitation of the Schumann–Runge continuum, longest band, and second band electronic states in O2

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