RFM Spectroscopic Data

17SEP19

Line Parameters

List of HITRAN parameters used by the RFM
SymbolParameter Units
ν0 Transition Wavenumber cm-1
S Line Intensity cm-1/(molec cm-2)
γair Air-broadened width cm-1 atm-1
γself Self-broadened width cm-1 atm-1
EL Lower-state energy cm-1
n Temperature dependence of γair [n/a]
δ Pressure shift cm-1 atm-1
V Vibrational quanta (for non-LTE) [n/a]
Q Rotational quanta (for line-mixing) [n/a]
HITRAN [
Web-site] is the most widely-used compilation of spectroscopic line parameters. The basic form consists of text records of 160-characters (.par file), one record for each transition, ordered by increasing wavenumber. The 2016 edition contained over 5 million records spanning 0–36000 cm-1. These are largely selected on the basis of their relevance to modelling the earth's atmosphere.

The parameters used by the RFM are listed in the table on the right.

While the RFM v5 can use this .par file directly, it can be quite slow, and the recommendation is to use the hitbin program to convert it to a binary format.

There are also some local FORTRAN programs for manipulating the HITRAN parameter files:

subhit
Subset HITRAN .par file. Can be used to reduce original .par file to containing only molecules/spectral range of interest.
mrghit
Merge HITRAN .par files. Can be used to merge different .par files, eg to replace molecule within the original file with a different set.
GEISA [Web-site] is an alternative source of spectroscopic line parameters. Structurally GEISA is similar to HITRAN, and contains the same set of essential parameters required by the RFM, but the records are formatted differently (and 252 characters in length). Also the list of molecules and isotopologues is slightly different. Although the RFM cannot read GEISA data records directly, a FORTRAN program is provided to convert GEISA to HITRAN .par format, which can then be read directly by the RFM, or converted to binary.
geihit
Convert GEISA 2015 data to HITRAN 2016 .par format

Absorption Cross-sections

Certain molecules, usually the more complex type, have lines which are too closely spaced to be resolved. For these, the absorption coefficient k(ν) [cm2/molec] is tabulated directly from lab measurements under particular pressure and temperature conditions. These are the HITRAN Absorption Cross-Section data files.

In HITRAN 2016 the data for each tabulation of k(ν) at a particular (p,T), (p in this case is measured in Torr, 760 Torr = 1 atmosphere) is provided as a separate file. Each tabulation is on a regular spectral grid, although not necessarily the same for all (p,T) — at lower pressures the spectral features start to resolve and higher spectral sampling is necessary.

The RFM expects cross-section data as a single file for each molecule, which can be constructed by simply concatenating the HITRAN files in any order of (p,T). Some caution is required here: the HITRAN data are often a collection from different sources and simply combining all the available data can lead to systematic errors when interpolating in the (p,T) domain (particularly noticeable when evaluating Jacobians). You are advised to only concatenate data from a single source.

Eg using the linux cat command to create a combined file sf6.xsc for data in the spectral range 925–955 cm-1

cat SF6*925*xsc > sf6.xsc

However, where the cross-section data covers different bands (eg 810–880 cm-1 and 1050–1120 cm-1 for CFC-11) all the data for each band should be concatenated first, and then data for the individual bands concatenated. For example, using the linux cat command with the CFC-11 (CCl3F) data to create a combined file f11.xsc

cat CCl3F*810*xsc CCl3F*1050*xsc > f11.xsc

GEISA [Web-site] absorption cross-section data are in a different format (although often from the same orginal source). As with the line parameter data, there is a Fortran90 program to convert from GEISA to HITRAN format:

geixsc
Convert GEISA 2015 absorption cross-section data to HITRAN .xsc format

HITRAN Collision-Induced Absorption

Collision Induced Absorption is a relatively new (since 2012) third type of HITRAN data. As with absorption cross-sections this is a tabulation of absorption coefficient as a function of wavenumber c(ν) but representing the absorption due to collisions between a specific pair of molecules rather than generic pressure broadening. As a consequence the absorption coefficient c is in units of cm5/molec2 (so that, mulitplied by the product of the densities of the two molecules, the result cρ1ρ2 is cm-1, as with conventional absorption kρ). The tabulations are only functions of temperature.

The data are available as single files for each pair of molecules, with all temperatures and spectral ranges contained in the same file. The ordering is band-by-band, and within each band, tabulations for different temperatures.

The RFM can use these data files directly.

HITEMP Data

HITEMP data is a line parameter compilation of including many more transitions for the major molecules which are only apparent at higher temperatures.

Since it is in the same 160-character format as the standard HITRAN line list the RFM can use these files either directly (RFM v5) or converted to binary format using hitbin. However since HITEMP contains only a limited set of molecules you might first want to merge this with the standard HITRAN list using mrghit.

RFM v5 uses the 2016 Gamache TIPS functions which are valid up to 9000K.

UV Data

Radiative transfer in the ultra-violet is dominated by molecular scattering so the RFM cannot be used to calculate meaningful radiances. However it is still useful for calculating the molecular absorption component.

The HITRAN 2016 line database extends into the UV (>25 000 cm-1, <0.4 µm) but only for a limited set of molecules with well-resolved lines: H2O (<25 711 cm-1), OH (<35 875 cm-1), HF (<32 352 cm-1) and H2 (<36 406 cm-1)

For other gases, absorptions are available as cross-section tabulations, in the same format as for the infrared heavy molecules, and so can be handled by the RFM in the same way. Note that for molecules which are normally represented in the infrared by HITRAN line data (eg O3) to specify cross-section data you have to append the letter 'x' (eg 'O3x') in the RFM driver table *GAS section - see also Recognised Molecules below, molecule numbers 171-184.

Recognised Molecules

The following is a list of all the molecules (Names in Red) recognised by RFM v5.02 If the last letter is 'q' this is a line molecule which is normally expected to be represented by tabulated cross-section data, and vice-versa for 'x'.

Internally the RFM assigns each molecule a number (set in subroutine molidx_sub.f90), although for tabulated cross-section data (.xsc files) it is possible to add arbitrary molecules which are, internally, assigned temporary numbers. This is possible for cross-section molecules since it is only necessary to associated the molecule's name with a matching cross-section file and atmospheric profile. However, for molecules described by line parameters, additional information such as molecular weight (for Doppler widths), permitted isotopologues and TIPS data is also required, requiring amendments to the code.
Molecules 1–49 follow the assigments for HITRAN 2016, 50–53 are extra molecules assigned these indices in the associated TIPS data, and 60–63 are assigned to additional molecules defined in the GEISA database.
ID Molecule ID Molecule ID Molecule ID Molecule ID Molecule
1 H2O 2 CO2 3 O3 4 N2O 5 CO
6 CH4 7 O2 8 NO 9 SO2 10 NO2
11 NH3 12 HNO3 13 OH 14 HF 15 HCl
16 HBr 17 HI 18 ClO 19 OCS 20 H2CO
21 HOCl 22 N2 23 HCN 24 CH3Cl 25 H2O2
26 C2H2 27 C2H6 28 PH3 29 COF2 30 SF6q
31 H2S 32 HCOOH 33 HO2 34 O 35 ClONO2q
36 NO+ 37 HOBr 38 C2H4 39 CH3OHq 40 CH3Br
41 CH3CNq 42 CF4q 43 C4H2 44 HC3N 45 H2
46 CS 47 SO3 48 C2N2 49 COCl2 50 SO
51 C3H4 52 CH3 53 CS2
60 GeH4 61 C3H8q 62 HNC 63 C2H6q
Key Standard HITRAN line molecules
HITRAN line data normally/better represented as cross-sections
Additional line molecule indices defined in 2016 TIPS data
Additional line molecule indices defined in the GEISA database
Molecules 100+ are RFM-specific indices for species represented by infrared absorption cross-section data.
ID Molecule ID Molecule ID Molecule ID Molecule ID Molecule
100 Aerosol
General Heavy Molecules
101 ClONO2 102 N2O5 103 SF6 104 CCl4 105 HNO4
106 SF5CF3 107 BrONO2 108 ClOOCl 109 X109 110 X110
CFCs (ChloroFluoroCarbons)
111 F11 (CCl3F) 112 F12 (CCl2F2) 113 F113 (C2Cl3F3) 114 F114 (C2Cl2F4) 115 F115 (C2ClF5)
116 F116 (C2F6) 117 F13 (CClF3) 118 F14 (CF4)
HCFCs (HydroChloroFluoroCarbons)
121 F21 (CHCl2F) 122 F22 (CHClF2) 123 F123 (CHCl2CF3) 124 F124 (CHClFCF3) 125 F141b (CH3CCl2F)
126 F142b (CH3CClF2) 127 F225ca (CHCl2CF2CF3) 128 F225cb (CClF2CF2CHClF)
HFCs (HydroFluoroCarbons)
131 F125 (CHF2CF3) 132 F32 (CH2F2) 133 F134 (CHF2CHF2) 134 F134a (CFH2CF3) 135 F143 (CF3CH3)
136 F143a (CF3CH3) 137 F152a (CH3CHF2) 138 F365mfc
MHCs (Methylated Hydrocarbons)
141 CH3OH (Methanol) 142 CH3CN (AcetoNitrile) 143 CH3CHO (Acetaldehyde) 144 Acetone (CH3COCH3) 145 PAN (CH3C(O)OONO2)
NMHCs (Non-Methylated Hydrocarbons)
151 C2H6x (Ethane) 152 C3H8 (Propane) 153 C6H6 (Benzene) 154 C2H2x (Acetylene) 155 C2H4x (Ethylene)
Halocarbons
161 C4F8 (Octafluorocyclobutane)
UV Cross-sections of simple molecules
171 O3x 172 N2Ox 173 SO2x 174 NO2x 175 H2COx
176 BrO 177 NO3 178 OClO
UV Cross-sections of heavy molecules
181 C7H8 (Toluene) 182 oxylene (o-C8H10) 183 mxylene (m-C8H10) 184 pxylene (p-C8H10)
Key Extinction cross-section [km-1]
Molecular cross-section [cm2/molec]
Dummy names for user-supplied cross-section molecules
Cross-section normally represented as HITRAN line data
Additional GEISA Cross-section molecules - RFM v4.31 onwards
UV Cross-sections - RFM v4.31 onwards
Some molecules are represented by both HITRAN line parameters and as cross-section data.

  • Where the RFM default is to use cross-section data (eg ClONO2, ID=101) the user can select the line data instead by adding 'q' after the molecule name (eg ClONO2q, ID=35).
  • Where the default is to use line data (eg C2H6, ID=27), the cross-section data can be selected by adding 'x' after the molecule name (eg C2H6x, ID=151).