Notes on cross section (Alan Heays, 2017-10-10)

An absolute photoabsorption cross section for the continuum A-X absorption is recorded by nee1985c between 112 and 145 nm, and the entire VUV photoabsorption spectrum is measured by electron-energy-loss spectroscopy by hitchcock1984, but with a 2 times greater absolute magnitude for the A-X transition. Subsequent calculations of the A-X transition (brown2000a, li_yuanjun2010) clearly favour the absolute magnitude (and absorption) profile of the nee1985c A-X measurement. I have then downscaled the entire spectrum of hitchcock1984 to match this (a factor of 0.53).

The photoabsorption recorded by nee1985c is extrapolated linearly from 145 to 165 nm to match the approximately point where the calculated cross sections of brown2000a and li_yuanjun2010 become zero.

A photoionisation yield measured by berkowitz1971 was rescaled by a factor of 1.47e-17 to match the cross section of hitchcock1984 (itself already rescaled) at its shortest wavelength, 62.5 nm. We assume 100% for this wavelength and shorter, which is roughly consistent with the branching measured by carnovale1981b.

I judge the overall uncertainty of the cross section to be about 30%.


Cross sections

Cross section figure.

[An explanation of the cross sections in this database]
[All cross sections — variable wavelength scale]
[All cross sections — variable wavelength scale in binary hdf5 format]
[All cross sections — 0.1nm wavelength scale]
[Photodissociation cross section — separate lines and continuum]
[Photoionisation cross section — separate lines and continuum]
[Download cross section figure as pdf]

Photodissociation and ionisation rates (s-1)

Radiation Photodissociation Photoionisation
ISRF 1.38e-10 0.00e+00
Mathis 9.85e-11 0.00e+00
4000K 5.31e-13 0.00e+00
10000K 2.88e-11 0.00e+00
20000K 1.17e-10 0.00e+00
Lyman-alpha 4.93e-10 0.00e+00
Solar 2.18e-11 2.45e-13
TW-Hya 3.19e-10 2.13e-12
Cosmic ray UV 1.84e-14 5.20e-24

[An explanation of the interstellar photo rates.]
[An explanation of the cosmic-ray induced photo rates.]
[An explanation of the radiation fields listed below.]
[Download all rates in a csv file.]

Shielding functions and fitted constants


Radiation γE2 γexp k0fit γfit Line data Dust data
ISRF 2.13 3.00 0.51 2.66 [Download] [Download]
Mathis 2.15 3.03 0.50 2.68 [Download] [Download]
4000K 1.65 2.40 0.61 2.15 [Download] [Download]
10000K 1.95 2.79 0.54 2.48 [Download] [Download]
20000K 2.14 3.01 0.49 2.66 [Download] [Download]
Lyman-alpha 2.11 2.97 0.58 2.70 [Download] [Download]
Solar 2.14 3.01 0.54 2.70 [Download] [Download]
TW-Hya 2.12 2.98 0.57 2.69 [Download] [Download]


Radiation γE2 γexp k0fit γfit Line data Dust data
ISRF - - - -
Mathis - - - -
4000K - - - -
10000K - - - -
20000K - - - -
Lyman-alpha - - - -
Solar 3.58 4.73 0.48 4.37 [Download] [Download]
TW-Hya 3.65 4.81 0.47 4.44 [Download] [Download]

[An explanation of the shielding functions and parameterisations.]
[Download all γ factors in a csv file.]
[Download all dust and line shielding functions in a zip file.]