Oscillator strengths (10-70 eV) for absorption, ionization and dissociation in H<sub>2</sub>, HD and D<sub>2</sub>, obtained by an electron-ion coincidence method

Backx, C.; Wight, G.R.; Wiel, M.J. van der

doi:10.1088/0022-3700/9/2/018

Cited by 113 publications

(46 citation statements)

References 29 publications

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“…Only transitions to those portions of the finalstate potential-energy curves lying within this region will be appreciably populated in the photoionization process, with the excess energy being carried off by the photoelectron. Although -2 % of the transitions to the ground Iso, ionic state of H: are dissociative [85], the photofragment energy is very low and is not separated from the very intense H,f peak in this work. The more energetic protons, which we are primarily concerned with, result from the dissociation of the three repulsive curves of H: lying above the lso, ground state.…”

Section: Photoion Angular Distributionsmentioning

confidence: 61%

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

Dehmer

1978

J. Phys. Colloques

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RCsumC. -Durant ces dix dernikres annees, les distributions angulaires des photo-electrons ont kte exclusivement utilisees pour ktudier la dynamique des processus de photoionisation dans les atomes et les molkcules. Nous faisons le point, ici, sur les resultats les plus marquants survenus depuis la dernikre Conference Internationale d'il y a trois ans. De loin, les plus grands progres ont eu lieu pour les atomes, l'interst s'etant plus particulierement port6 sur les points suivants : amelioration de l'ordre zero (Hartree-Slater, Cooper-Zare), comprehension du paramttre d'asymetrie P(&), en considerant les correlations Clectroniques, les effets relativistes, les interactions de 1'Ctat final anisotropique. L'etude des gaz rares a bkneficik de l'ttroite coordination entre l'expkrience et la theorie, tandis que l'etude des atomes non spheriques est restee principalement theorique, mis a part les mesures rkcentes sur I'oxygkne atomique. Les etudes de distribution angulaire sur les molecules sont encore a un stade t r b preliminaire de dtveloppement. Ceci resulte du manque de mesures en fonction de la longueur d'onde, mises a part les experiences trks recentes, et l'absence de methodes theoriques pratiques et realistes. Le point sera donc fait sur ce travail recent, ainsi que sur une selection de travaux plus anciens concernant les molCcules et obtenus avec des raies de resonance. De plus, une nouvelle serie d'ktudes angulaires sur les molCcules -la distribution angulaire des ions non thermiques formes par photoionisation dissociative -fournissant des informations complCmentaires sur les mesures correspondantes avec des photoClectrons, sera presentee.Abstract. -During the last ten years, photoelectron angular distributions have been used extensively to study the dynamics of the photoionization process in atoms and molecules. Here we review some major advances in this body of work, with special emphasis on results emerging since the last Conference on VUV Radiation Physics three years ago. By far the greatest progress has occurred for atoms, where interest is focussed on improving our zero-order (Hartree-Slater, Cooper-Zare) understanding of the asymmetry parameter P(&), by considering electron correlations, relativistic effects, and anisotropic final-state interactions. The study of the rare gases has benefitted from extensive coordination between experiment and theory, whereas work on non-spherical atoms has been mainly theoretical, with the only measurements being performed very recently on atomic oxygen. Angular distribution studies on molecules are in a much earlier stage of development. Progress has been impeded by the lack of practical, realistic theoretical methods and wavelength-dependent measurements, both of which are becoming available only now. This recent work, together with selected topics from earlier resonance-line work on molecules will be reviewed. In addition, a new class of angle-dependent stud~es of molecules will be discussed -the angular distribution of non-thermal ions formed by dissociative ph...

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Section: Photoion Angular Distributionsmentioning

confidence: 61%

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

Dehmer

1978

J. Phys. Colloques

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“…Hence, although O 2 is the dominant species, there is no absorption by it at the Lyα. A low cross-section is also measured for H 2 (Backx et al 1976) and the optical depth will be similarly low due to the lower abundance of H 2 compared to O 2 . The absorption cross-sections of H 2 O and OH (Nee & Lee 1984;Yoshino et al 1996Yoshino et al , 1997 both peak near the Lyα line and assume a similar value of ∼1.5×10 −17 cm 2 at 1216 Å.…”

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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“…The lack of spectral resolution in this kind of experiment does not lead to an underestimate of unresolved features, in contrast to direct photoabsorption measurements, because of the linear relation between cross section and the signal from the analysed electrons. Electron-energy-loss cross sections can be recorded for energylosses spanning the entire photoabsorbing wavelength range and then absolutely calibrated according to the Thomas-ReicheKuhn sum rule (Backx et al 1976) without detailed knowledge of the sample column density. These kinds of experiments typically yield an uncertainty of 30% or better but can not resolve the detailed wavelength structure of many molecules.…”

Section: Experimental Cross Sectionsmentioning

confidence: 99%

“…The resultant photoions and photoelectrons can be experimentally manipulated with electric fields and detected with high-efficiency, possibly simultaneously (e.g., Backx et al 1976;Holland et al 1993;Edvardsson et al 1999). When all fragments are simultaneously detected, it is possible to spectroscopically examine the initial neutral species and produced ions.…”

Section: Experimental Cross Sectionsmentioning

confidence: 99%

Photodissociation and photoionisation of atoms and molecules of astrophysical interest

Heays

Bosman

Dishoeck

2017

A&A

428

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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Oscillator strengths (10-70 eV) for absorption, ionization and dissociation in H₂, HD and D₂, obtained by an electron-ion coincidence method

Cited by 113 publications

References 29 publications

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

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

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Oscillator strengths (10-70 eV) for absorption, ionization and dissociation in H2, HD and D2, obtained by an electron-ion coincidence method

Cited by 113 publications

References 29 publications

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

Angular Distributions of Photoelectrons and Non-Thermal Photoions From Atoms and Molecules

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

Contact Info

Product

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About

Oscillator strengths (10-70 eV) for absorption, ionization and dissociation in H₂, HD and D₂, obtained by an electron-ion coincidence method