(B) “Hybrid” compressed 12CH4 data designed for a fast spectra modeling.
( release of November 2017 )
At high the CH4 spectra are very congested including many millions (T > 400 K ) or even billions (T > 1000 K ) of transitions ( see refs [1,2]). To accelerate a modeling of spectral functions in these cases the initially computed full LbL lists are partitioned into two sets as described in Ref  :
(b1) “Light lists” contain three columns ( WN /cm-1, I/ cm*molec-1, E_low/cm-1) for strong and medium transitions necessary for an accurate description of sharp features in absorption/emission spectra.
The exhaustive light list sets are provided from T=100 K to T= 2000 K with the step of dT = 100 K according to wavenumber ranges specified in Table below.
(b2) For a fast and efficient modeling of quasi-continuum (QC) cross sections, billions of tiny lines are compressed in “super-lines” (SL) libraries . Each “super-line”  represents the sum of intensities of all very weak transition at a given temperature over the wavenumber range d_WN. In the present release the wavenumber step was chosen constant d_WN = 0.005 cm-1. The temperature step for super-lines is dT = 20 K. They are tabulated with this steps from T=100 K to T= 2000 K according to wavenumber ranges specified in Table 1 ( below) containing three columns ( WNs /cm-1, Is/ cm*molec-1, Ns).
WNs = wavenumber at the predefined grid, Is = sum of QC lines, Ns = number of summed lines for QC)
Warning (!) : For a correct use of these “hybrid” data sources, the spectral functions computed from (b1) “Light lists” and from (b2) “quasi-continuum” must be summed together. Otherwise , a part of the opacity would be missing.
Instruction for the users for the hybrid data:
Both true “Light lists” and compressed “super-lines” libraries are accessible to download.
If you need a XS simulation at the temperature T_user.
- Then take the “Light list” at the nearest T >= T_user. Recalculate intensities of provided individual true lines to your T_user using E_low and the partition functions. Choose line width on your convenience and generate your “Light list” absorption/emission simulation.
- Take the superline lists (SL) at the nearest T ~ T_user . Convert the QC absorption coefficient to your needed spectral function.
- Finally you must sum up your spectral function simulations originated from “Light list” (b1) and from QC (b2) in the total computed spectrum.
- Because of the compression [1,3] , the superline does not have a E_low and thus cannot be easily recalculated to another temperature , which is very different from the specified T. The user could make an Is interpolation from the nearest T >= T_user and T =< T_user in the provided SL libraries.
- As a default option for QC simulation, it is advised to use the same broadening coefficients for SLs as for true strong lines. For simulations with low resolution it is advised to apply to SLs the same "apparatus function" convolutions as for strong lines. For simulations with high spectral resolution ~ 2* d_WN = 0.01 cm-1 one has to give a profile to the superlines with line-width > d_WN = 0.005 cm-1.
Online simulations at the TheoReTS site:
Both contributions from (b1) and (b2) data sources are automatically accounted for spectral functions. A detailed discussions and instructions for the use of “hybrid” data sources in case of high-T methane spectra can be found in .
Warning: The graphical tools cannot support online simulations in too large WN ranges. For the corresponding requests the user is invited to download (b1) and (b2) data and make simulations on his (her) own computer.
Click here to access to "Hybrid" data directory
To download the data, you can use any program to retrieve files from the World Wide Web using HTTP, like wget, Download Master, Fresh Download etc.
- Rey, M., Nikitin, A.V., Tyuterev, V.G. “Theoretical hot methane line lists up to t = 2000 k for astrophysical applications”. Astrophysical Journal, 789 (1), art. no. 2, (2014); doi: 10.1088/0004-637X/789/1/2.
- Rey, M., Nikitin, A.V., Tyuterev, V.G. “Accurate Theoretical Methane Line Lists in the Infrared up to 3000 K and Quasi-continuum Absorption/Emission Modeling for Astrophysical Applications”. Astrophysical Journal, 847 (2), art. no. aa8909 (2017); doi: 10.3847/1538-4357/aa8909.
- M. Rey, A.V. Nikitin, Y. Babikov, V. Tyuterev, TheoReTS - An information system for theoretical spectra based on variational predictions from molecular potential energy and dipole moment surfaces // JMS, 2016, doi:10.1016/j.jms.2016.04.006.