# HITRAN¶

ExoCross can be used with the standard HITRAN line list by adding the HITRAN keyword anywhere in the input file (outside any sections). This will also require the partition function (pf) and isotopologue number (iso) defined.

HITRAN broadening parameters will be used unless the species-section is given, which specifies the broadening. The .states file is not required and ignored if given. The HITRAN total statistical weights are used directly.

For example:

Temperature  296.0
Range 0.0  10000.0

Npoints 10001

absorption
gauss
hwhm 0.5 (cm-1)

hitran
iso 26 1
pf 1000.0

output C2H2_ab_g0.5
Transitions  26_hit12.par


Here iso can appear in a HITRAN form as, e.g. 261.

HITRAN keyword can also also used for writing in the HITRAN output. In this case the broadening parameters are expected to be specified for air and self as part of the SPECIES section, including delta. To invoke HITRAN output use WRITE next to the HITRAN keyword, which starts a section, which should be ended either by END or an emty line. The ID_ISO should be also specified using ISO keyword.

Temperature  1900.0
Range 0.0  10000.0

absorption
stick
threshold -1e-25

hitran write

iso 28

pressure  1.0
species
air   gamma 0.0155 n 0.41 t0 298.0  ratio 0.82 delta 0.000
self  gamma 0.1070 n 0.77 t0 298.0  ratio 0.18 delta 0.000
end

mass 40.0

output NO_1900K_HITRAN

States 15N16O.states



The following example allows one to specify the error codes (6 values) for the HITRAN format outputs. It is still a part of the HITRAN WRITE section, the six keywords (error-E, error-S, error-Air, error-self, error-delta) start lines with the corresponding specifications. The Energy and Intensity (S) lines are used to give the ranges of he quantum numbers for different error codes. The other four can hold only one error code.

hitran write
error-E  qn 4 ierr 4  vmax  10 ierr 3  vmax  20 ierr 2  vmax  30  ierr 1  vmax  40 ierr 0  vmax  100
error-S  qn 4 ierr 5  vmax  10 ierr 4  vmax  20 ierr 3  vmax  100
error-Air   ierr 4
error-self  ierr 4
error-n     ierr 4
error-delta ierr 0
end


Here write indicates that the HITRAN-stick-like list will be printed.

qn 4 indicates the quantum number (4th column in States after J’s columns);

ierror 4 vmax 10 means that the error code 4 is applied for all values of qn less or equal to 10 etc.

error-Air ierr 4 indicates that the error code for the Air-broadening is 4.

The absorption spectrum using HITRAN can be computed using the HITRAN reference intensity:

$$I(T)=I(T_{\rm ref}) \frac{ \exp(-c_0 \tilde{E}''/T) \left(1-\exp(-c_0\tilde{\nu}/T)\right) Q(T_{\rm ref})}{\exp(-c_0 \tilde{E}''/T_{\rm ref}) \left(1-\exp(-c_0\tilde{\nu}/T_{\rm ref})\right) Q(T)}$$

where $$T_{\rm ref}$$ and $$Q(T_{\rm ref})$$ are the reference temeprature (296 K) and the corresponding reference partition function. This expression is always used if $$Q(T_{\rm ref})$$ is provided: The reference temperature is assumed 296 K (HITRAN standard). It can be changed via

pf 100000. ref 30000.


Otherwsie the standard absorption expression is amployed. The reference temperature is assumed 296 K (HITRAN standard). It can be changed via

Temperature  1000 ref 173


The intensity cut-off (stick) can be done using the HITRAN method: $$S=S_{0} \tanh(c_2 \nu/2T)$$ for $$\nu\le 2000$$ cm $$^{-1}$$ and $$10^{-29}$$ cm/molecule above.

absorption
stick
cutoff HITRAN (S_crit) 1e-29  nu_crit 2000

output ScH_1500K_box_stick
States       ScH.states
Transitions  ScH.trans


# VALD¶

The Vald format has the following structure:

lambda E_low_eV loggf 0.0 gtot_f 0.0

where lambda is the wavelength in nm, E_low_eV is the energy of the lower state in eV, loggf is log10(gf), gf is the gf factor in the Physics (ExoMol) convention, gtot_f is the total degeneracy in the ExoMol convention. To convert to the Astrophysics convention, the keyword gf_factor canm be used.

Here is an example to generate a Vald-formatted line list for 13C__8states using gf_factor 0.25 to convert to he Astrophysics convention. Here, the nuclear statistical weights are 1 (A1,A2) and 3 (B1,B3), which gives the factor 1/(1+3) = 1/4.

Temperature  8000
Range 1000 30000

vald
gf

gf_factor 0.25
threshold 1e-99

output 13C2__8states_vald_T8000K_1e-99_10000-30000

States 13C2__8states.states
Transitions 13C2__8states.trans