RFM Spectroscopic Data | ||
14NOV24 |
Symbol | Parameter | Units |
---|---|---|
M | Molecule number | [n/a] |
I | Isotope number | [n/a] |
ν | Vacuum Wavenumber | cm-1 |
S | Intensity | cm-1/(molec cm-2) |
γair | Air-broadened half-width | cm-1 atm-1 |
γself | Self-broadened half-width | cm-1 atm-1 |
E" | Lower-state energy | cm-1 |
nair | Temperature dependence exponent for γair | [n/a] |
δair | Air pressure-induced line shift | cm-1 atm-1 |
V',V" | Vibrational quanta (via HITBIN, for non-LTE) | [n/a] |
Q',Q" | Rotational quanta (for CO2 line-mixing) | [n/a] |
The basic form consists of text records of 160-characters (.par file), one record for each transition, ordered by increasing wavenumber.
The 2020 edition contained over 7 million records spanning 0–7×106 cm-1 (i.e. wavelengths down to 1.4 nm), for 55 different molecules.The parameters used by the RFM are listed in the table.
While the RFM 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. The binary format is also required for non-LTE calculations, selection of vibrational bands and use of the internal CO2 line-coupling model.
There are also some local Fortran/Python programs for manipulating the HITRAN parameter files:
A limitation of the standard HITRAN .par format is that it does not allow for any additional line parameters beyond the basic set required for the standard Voigt lineshape, and even those are restricted to measurements with 'air' as the broadening gas (with the exception of self-broadened half-width).
Nowadays HITRAN is actually a database, and the 160-character .par line list is just one way of accessing the information. In fact the user has complete flexibility in extracting any subset of parameters in any order in different formats [Example].
Unfortunately this flexibility makes reading the extracted data more complicated and, unlike the standard .par structure, there is no guarantee that valid data exists for all the selected fields (in fact most of the 'non-standard' fields are filled with '#' characters, i.e., blank), so any code reading the data has to make decisions on whether to ignore the line completely or use default values.
See [HITRAN Database Files] for RFM implementation.
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).
It is generally recommended that only data from a single source is combined.
Eg using the linux cat command to create
a combined file sf6.xsc for data in the spectral range
925–955 cm-1
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.
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.
[Note: for RFM v5.10 and later versions,
the files can be
concatenated in any order]
For example, using the linux cat command with the CFC-11 (CCl3F) data
to create a combined file f11.xsc
HITRAN Collision-Induced Absorption
Collision Induced Absorption data are a
relatively new (since 2012)
third type of HITRAN spectroscopic data. As with
absorption cross-sections
these are tabulations 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.
Since it is in the same 160-character
.par file format as the standard HITRAN line
list the RFM can use these files either directly or converted
to binary.. 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 uses the 2020 Gamache TIPS functions
which are valid up to 9000K.
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.
GEISA line data
[format]
contains the same set of
essential parameters required by the RFM, but in a different format.
Also the list of molecules and
isotopologues is slightly different to HITRAN. The RFM cannot read GEISA
data records directly, but 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.
GEISA
absorption cross-section data
[format]
are also in a different format to HITRAN (although often from
the same orginal source).
As with the line parameter data, there is a Fortran convversion program:
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.
HITEMP Data
HITEMP data is a line parameter compilation including many more transitions
for the major molecules which are only apparent at higher temperatures.
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.
GEISA Data
GEISA
[Web-site]
is an alternative source of spectroscopic line parameters and cross-section
parameters.
Recognised Molecules
The following is a list of all the molecules
(Names in Red)
recognised by RFM.
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'.
Molecules 1–55 follow the assigments for HITRAN 2020, 56 –57 are extra molecules assigned these indices in the associated TIPS data, and 61–63 are assigned to additional molecules defined in the GEISA 2015 database. | |||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
ID | Molecule | ID | Molecule | ID | Molecule | ID | Molecule | ID | Molecule | ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
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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 | CH3F*
| 52 | GeH4*
| 53 | CS2
| 54 | CH3I
| 55 | NF3
| 56
| C3H4
| 57
| CH3
| 60
| *
| 61
| C3H8q
| 62
| HNC
| 63
| C2H6q
| Key
| Standard HITRAN line molecules
|
| *Changed with RFM v5.2. Was
(51) C3H4, (52) CH3, (60) GeH4, while 53–57 were undefined
|
| HITRAN line data normally/better represented
as cross-sections
|
| Additional line
molecule indices defined in 2020 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 |
| |