.cia File

RFM File Formats: Collision-Induced Absorption Data

26OCT23

Type
Input(s), mandatory if collision-induced absorption is to be used

Description
Collision-Induced Absorption cross-sections [cm5/molec2] for pairs of molecules, tabulated for particular wavenumber ranges at different temperatures.

Filename(s)
Specified in *CIA section of the Driver Table.

Structure
This is the HITRAN file format, although the optional initial comment records are an RFM extension.
An individual file consists of a concatenated set of tables for one pair of molecules, usually ordered by temperature (inner loop) then spectral band (outer loop), but the RFM makes no assumption about the internal ordering.
The tabulation for a particular molecule pair, wavenumber range and temperature (as described below) consists of a 100-character formatted header record followed by a series of records each containing a (wavenumber,absorp.coeff) pair.
File Structure
For iBnd = 1, NBnd Loop over arbitary number of spectral bands
  For iTem = 1, NTem Loop over arbitary number of temperatures
    !CMNT Comment record(s) (optional)
    MOLEC   WMIN   WMAX   NPT   TEM   AMAX   RES   CMT   REF C100 Header record[1]
    For i = 1, NPT Loop over NPT spectral points
      WNO(i) CIA(i) Separate record for each point

Fields
Field Format Description Units Range
!CMNT A80 Comment record(s) (optional) Record starts with '!'
MOLEC A20 Chemical Formula, right justified eg 'N2-O2'
WMIN F10.3 Lower Wavenumber of tabulation cm-1 0< : WMAX
WMAX F10.3 Upper Wavenumber of tabulation cm-1 WMIN :
NPT I7 No. of tabulated points 0< :
TEM F7.1 Temperature of tabulation K 0< :
AMAX E10.3 Max value of CIA cm5/molec2 0< :
RES F6.3 Resolution cm-1 0< :, or -.999 if irreg.
CMT A27 Comment
REF I3 Reference index
WNO(:) F10.4 (NPT) Wavenumber value cm-1 WMIN : WMAX
CIA(:) E10.3 (NPT) CIA value [3] cm5/molec2 ~0[4] : AMAX

Notes
  1. The RFM only reads the following fields from the Header records: MOLEC, WMIN, WMAX, NPT, TEM.

  2. On input, the RFM will extract the subset of the tabulated spectral ranges which overlaps the min/max wavenumbers required for the RFM calculations (as specified in the *SPC section). A message appears in the RFM log file specifying the range used, as well as the number of temperature tabulations, eg:
    I-CIAFIL: 2199.9000 - 2300.0600 cm-1 read 9 Temps from 228.2 - 362.5 K

  3. CIA values are of the order of 1E-45, which is smaller than can be stored as a FORTRAN REAL variable. Therefore, internally, the RFM multiplies these values by (Avogadro's number ~ 6E26)2, converting units from cm5/molec2 to cm5/kmol2.

  4. CIA values are sometimes negative, arising from noise on the measurement. These values are set to zero on input.

Example
O2-O2_2011.cia (HITRAN O2 self-broadening).

Software
read_cia.py (Python function to read CIA file)