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4.1. Testcase #1

In this example we calculate the population ratios of the 3PJ ground levels of atomic carbon as a function of neutral hydrogen density. These population ratios are a useful density estimator [19] and are needed to interpret ratios of UV C I fine structure absorption lines observed in damped Lyman-alpha QSO absorbers [20, 21, 22], for example.

We take into account collisions with several collisional partners - electron, proton, neutral hydrogen, para/ortho molecular hydrogen, neutral helium -, tying their densities to the neutral hydrogen density nH0 according to:

Equation 22 (22)

We also take into account the effect of CMBR at a redshift z = 1 and the radiation field of the Galaxy.

In the high density limit, function LTEDEV is called to show that the population ratios differ from LTE conditions by less than 4% .

To run this testcase the user should include the radiation field of the Galaxy in the body of function URAD in module POPRATIO:

urad = Fgal(lambda)