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 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
Transitions NO_128_N15.trans.head
The local quantum numbers in the HITARN output includes J follows by QNS specified the QN structure as the column number in the State file using the keyword local (or ``rot):
QN
local 7
end
The global quantum numbers are taken from States file (starting from column 7 by default, after uncertanty and lifetimes columns) and can be listed in the QN using the Global (vib) keyword:
QN
global 8 9 10
end
Here 8,9,10 are the columns in .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
error-nu
end
Here error-unc is to define the energies/frequency error codes using the ExoMol uncertanties from column 5 in States file using ierr = \(int(1-log10({\rm unc}))\), where unc = \(\sqrt{{\rm unc}_i^2+{\rm unc}_f^2}\) using the corresponding uncertanties of the initial and final states, respectively.
error-E and error-S define HITRAN error codes (integer) of the frequencies and intensities based on the quantum numbers: qn defines the QN column (starting from the state ID coulmn =1), ierr is the errro value and vmax is used to define the range of the quanrum numbers this error code is applied to. here ierr = 4 for QN(4) = 0…10, ierror = 3 for QN(4) = 11…20 etc.
error-Air, error-self, error-N, error-delta define HITRAN error codes (integer) of the corresponding line shape parameters.
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
A complete example for an SO line list:
Temperature 296
Range 0.0 45000.0
absorption
stick
threshold -1e-30
hitran write
iso 50 1
QN
global 8 9 10 11
local 7
end
hitran write
error-E ierr 1
error-S ierr 3
error-Air ierr 0
error-self ierr 0
error-n ierr 0
error-delta ierr 0
error-unc
end
abundance 0.947926
pressure 1.0
species
air gamma 0.8000 n 0.50 t0 296.0 delta 0.000
self gamma 0.8000 n 0.50 t0 296.0 delta 0.000
end
output SO_298K_HITRAN
States 32S_16O__SOLIS_MARVELised.states
Transitions 32S-16O__SOLIS.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