Cross-Sections ============== The method is described in: C. Hill, S. N. Yurchenko, J. Tennyson, "Temperature-dependent molecular absorption cross sections for exoplanets and other atmospheres", Icarus, 226, 1673-1677 (2013). `See the paper here`_. .. _See the paper here: http://www.sciencedirect.com/science/article/pii/S0019103512003041 Gaussian profile ^^^^^^^^^^^^^^^^ Example (HWHM is the half-width at half-maximum): :: Temperature 2000.0 Range 0.0 12000.0 Npoints 200001 absorption Gaussian HWHM 0.5 (cm-1) threshold 1e-40 (to skip weak lines) output abs_gauss_0.5_T2000.0 States "../all/ch4-50.states-all" Transitions a-03000.dat a-03100.dat a-03200.dat a-03300.dat a-03400.dat a-03500.dat a-03600.dat a-03700.dat a-03800.dat a-03900.dat end Doppler profile ^^^^^^^^^^^^^^^ Doppler_ is the effective mass of the molecule in amu. .. _Doppler: https://github.com/Trovemaster/exocross/blob/master/img/alpha.png Example: :: Temperature 1500.0 Range 0.0 12000.0 Npoints 200001 emission doppl mass 16.0313 output dop_emiss_1500.0 States ch4-50.states-all Transitions a-02100.dat Lorentzian profile ^^^^^^^^^^^^^^^^^^ Here b is the normalization factor. Example: :: Temperature 300 Range 0.0 10000.0 Npoints 10001 absorption Loren HWHM 0.1 (cm-1) output abs_lor_0.1_T300.0 States NaH.states Transitions NiH.trans Stick spectrum ^^^^^^^^^^^^^^ Example: :: (ScH stick spectrum) Temperature 1500.0 Range 0. 16000.0 Npoints 16001 absorption stick threshold 1e-29 output ScH_1500K_stick States ScH.states Transitions ScH.trans bin ^^^ is to produce average intensity per the wavenumber or wavelength interval as defined by Range/(Npoints-1). The wavelength is invoked by adding um to the range values. Example: :: (ScH bin spectrum) Temperature 1500.0 Range 0. 16000.0 Npoints 16001 absorption bin output ScH_1500K_bin_stick States ScH.states Transitions ScH.trans or: :: (ScH bin spectrum) Temperature 1500.0 Range 1. 100.0 um (or micron) Box ^^^ Is to plot the maximal transition intensity per wavenumber interval, which is a cheaper alternative for the stick spectrum Example: :: (ScH box spectrum) Temperature 1500.0 Range 0. 16000.0 Npoints 16001 abundance 0.97 absorption box threshold 1e-29 output ScH_1500K_box_stick States ScH.states Transitions ScH.trans Line-width cut-offs ^^^^^^^^^^^^^^^^^^^ A line width cut-off can be defined using ``cutoff`` or ``line-cutoff`` :: cutoff 25 (cm-1) :: line-cutoff 25 (cm-1) where the offset value is in wavenumbers (cm-1). The default value is 25 cm-1. Alternatively, one can define the cut-off in terms of the HWHM as follows: :: cutoff 50 HWHM multi-grid ^^^^^^^^^^ A multi-grid with regions of different resolutions can be defined using the following `grid` section: :: grid Range 0 100 Npoints 10000 cutoff 10 Range 100 1000 Npoints 1000 cutoff 25 Range 1000 10000 Npoints 100 end The maximal number of sub-grids is 100. Currently this option only works with simple sampling-type profiles, such as `Voigt`, `Doppler Sampling`, `Gaussian Sampling` or `Bin`. The latter is commonly used to generate super-lines. `cutoff` or `line-cutoff` is an optional keyword to allow region-dependent cutoffs for line profiles. If undefined, the value of the global keyword `cutoff` the corresponding default value (25 cm-1) is used. gf line list ^^^^^^^^^^^^ A stick spectrum is produced with the gf-factors in place of the Einstein coefficients. Here is the example for the VALD format, where the columns are the wavelength in Angstrom, the lower state energy in eV, log10(gf), 0.0, the statistical weight 2J'+1 (upper state J') and zero. :: temperature 5000 Range 100. 16000.0 gf vald threshold 1e-29 output ScH_gf States ScH.states Transitions ScH.trans Using HITRAN .par with ExoCross ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Here is an example of an ExoCross input file for computing absorption cross sections from a HITRAN .par with ExoCross: :: Temperature 400 Range 0 8000 Npoints 800001 absorption voigt pf 274.56910 ref 1.74581257E+02 HITRAN mass 18 iso 1 1 abundance 0.99734 pressure 1.0 transitions HTRAN_H2O_2020.par species air gamma 0.075 n 0.40 t0 296.0 ratio 0.70 delta 0.000000 self gamma 0.670 n 1.00 t0 296.0 ratio 0.30 delta 0.000000 end output H2O_HITRAN_400K_voigt_1bar It is important to provide two partition functions, for the target temperature (here 400 K) as well as for 296 K (HITRAN reference temperature). One also needs to define the air:self ratio as well as as the mass, isotopologe number etc.