The GEISA-2015 sub-database of absorption cross-sections

Besides the line transition parameters data catalog itself, GEISA includes, a second catalog, providing, at various temperatures and pressures, the cross-sections of molecules for which spectral line parameters are incomplete or unavailable; generally these are ‘large’ molecules for which the generation of line parameters is very difficult.

As in the previous editions of GEISA, the absorption cross-sections σ (ω), expressed in cm2 molecule-1 , at a given wavenumber ω, are determined through the following expression:

σ (ω)= ( ln [ I0(ω) / I(ω) ] ) / n*l


and where :

  • ln is the natural logarithm
  • ω is the wavenumber (cm-1)
  • I0(ω) and I(ω) are the intensities at wavenumber ω , of the incident and transmitted radiation, respectively
  • n is the number of absorbing molecules (molecule cm-3)
  • l is the optical path length (cm)

Starting from the previous GEISA 2011 archive as described in Jacquinet-Husson et al. (2008, 2011), the 2015 version has been enriched by several molecular species in a larger spectral range Cross-sections are available in two spectral regions: the infrared and the ultraviolet/visible.

It should be noticed that pressure and temperature ranges depend on the molecular species and on the data sources.


  • In the Infrared :

In the spectral range 200 – 6500 cm-1, 39 molecular species already archived, in GEISA-2011, were kept, i.e.: CFC-13, CFC-113, CFC-114, CFC-115, CFC11, CFC12, CFC14, HCFC22, HCFC123, HCFC124, HFC125, HFC134a, HCFC141b, HCFC142b, HFC152a, HCFC225ca, HCFC225cb, HFC32, HFC143a, HFC134, N2O5, SF6, ClONO2; HFC-143, HCFC-21, CCl4, C2F6, C2H2, C2H4, C2H6, C3H8, C4H8, HNO4, SF5CF3, HCH-365mfc, C6H6, CH3CN, C2H3NO5, (CH3)2CO.

Five molecular species, already present in GEISA-2011, were updated, i.e.: in the TIR (Thermal InfraRed): CFC-12, C2 H6 , C3 H8 (Propane), (CH3)2CO (Acetone); in the TIR and in the NIR (Near InfraRed), CH3CN (Acetonitrile).

New :
In the spectral range 25 – 7497 cm-1, 41 new molecular species were included in GEISA-2015:
– In the spectral interval 25 – 4800 cm-1, 35 molecular species, i.e.: CF2=CF2 (PFC-1114), CF3CF=CF2 (PFC-1216), CF2=CFCF=CF2, CHF2OCF2CF2OCHF2 (HFE-338pcc13), HF2OCF2OCHF2 (HFE-236ca12), (CF3)2CHOCH2F (Sevoflurane), CHF2OCHClCF3 (Isoflurane), (CF3)2CFC(O)CF2CF3 (Perfluoro(2-methyl-3-pentanone), CHF2CF2CH2OCH3, CF3CF2CH2OCH3, CF3CH2OCH2CF3, (CF3)2CHOCH3, CHF2CHFOCF3, CF3CHFOCF3, CHF2OCHFCF3, CF3CHFCF2OCH2CH3, CF3CF2CF2OCHFCF3, CHF2OCH2CF3, CF3CH2OCH3, CF3CFHCF2OCF2H, CH2FCH2OH, CHF2CH2OH, CF3CH2OH, CF3CF2CH2OH, CHF2CF2CH2OH, CF3CF2CF2CH2OH, CF3CHFCF2CH2OH, CF3CH2CH2OH, CF3(CH2)2CH2OH, CF3CHO, CF3CH2CHO, CF3(CH2)2CHO, CH3OH (Methanol), CHF3 (HFC-23), CH3CHO (Acetaldehyde)

– In the near infrared (NIR), spectral interval 6600 – 7497 cm-1, 6 molecular species, i.e.: CH3I (Methyl iodide), CH3O2 (Methyldioxidanyl), H2CO (Formaldehyde), HO2 (Hydroperoxy radical), HONO (Nitrous acid), NH3 (Ammonia).


  • In the Ultraviolet/Visible :

No update occurred in this spectral region. The GEISA 2011 database content has been kept, in the spectral range 7750 cm-1 to 51282 cm-1, for the following molecules and radicals: NO2, CS2, O3, SO2, O2, O2-O2, O2-N2, OClO, H2CO, OBrO, BrO, IO, OIO, and aromatic hydrocarbons; these are C6H6, C7H8 and the three isomers of (C6H4(CH3)2, as well.