Measurements and modelling of high pressure pure CO2 spectra from 750 to 8500cm-1. I central and wing regions of the allowed vibrational bands.

Precisemodellingofinfraredabsorptionbycarbondioxideisofprimaryimportancefor radiativetransfercalculationsinCO2-rich atmosphereslikethoseofVenusandMars. Despitevariousmeasurementsandtheoreticalmodelsdedicatedtothissubject,accurate data atdifferenttemperaturesandpressuresarestilllackinginnumerousspectral regions.Inthiswork,usingtwoFourierTransformSpectrometers,wehavemeasured spectraofpureCO2 in alargespectralregionrange,from750to8500cm-1 at various densities(3–57amagat)andtemperatures(230–473K).Comparisonsbetweenmea- sured dipolarabsorptionbandsandspectracalculatedwiththewidelyusedLorentzline shapeshowverylargediscrepancies.ThisresultisexpectedsincetheLorentzapproach neglectsline-couplingeffectsduetointermolecularcollisionswhichtransferabsorption from thewingstothebandcenter.Inordertoaccountforthiseffect,atheoretical approachbasedontheimpactandEnergyCorrectedSuddenapproximationshasbeen developed.Comparisonsofthismodelwithnumerouslaboratoryspectrainawiderange of pressure,temperatureandspectraldomainshowsatisfactoryagreementsforband centersandnearwingregionswheretheimpactapproximationisvalid.However,as expected,duetothebreakdownoftheimpactapproximation,themodelfailswhen consideringfarwingregions.Intheabsenceofprecisemodelsaccountingforline-mixing and finite collisionduration(nonimpact)effects,empiricalapproximationsareproposed in ordertomodelthefarwings.