Misure ottiche su atmosfere planetarie in laboratorio

1. La ricerca dei pianeti extrasolari in Italia, 5-7 nov. 2014, Roma EXO-IT Misure ottiche su atmosfere planetarie in laboratorio Marcel Snels1, Stefania Stefani2 1) Institute of Atmospheric Sciences and Climate (ISAC) 2) Institute for Space Astrophysics and Planetology (IAPS)

2. OUTLINE • Rationale of the work • Experimental setup: • Measurements of CO2 transmittance using a venusian real vertical profile • Collision Induced Absorption (CIA) bands • Study of the continuum • Study of the weak absorption • Conclusions • High Pressure-High Temperature gas cell • Cavity Ring Down • Multi Pass gas cell

3. Rationale of the work Several databases are available: • HITRAN (HIgh resolution TRANsmission), (Rothman LS et al et al. 2009) • HITEMP (HIgh TEMPerature), (Rothman LS et al et al. 2010) • CDSD (Carbon Dioxide Spectroscopic Databank), (Tashkun S.A.; et al 2006) Laboratory measurements of the optical properties of gases at planetary conditions is of great importance to support radiative transfer modelling relevant for remote sensing instruments and retrieved chemical-physical products

4. Experimental setup FT-IR Specification: Detectors: DTGS 350-10000 cm-1 MCT 850-12000 cm-1 InGaAs 9000-12.800 cm-1 Si 9000-25000 cm-1 Sources: MIR 100-8000 cm-1 NIR/VIS 3000-25000cm-1 Beam splitter: KBr 380-10000 cm-1 CaF24000-50000 cm-1 Resolution (10-0.07) cm-1

5. High Pressure High Temperature Gas cell Optical parameters • Pressure up to 300 Bar • Temperature up to 310 °C • Optical path: l ≈ 2 cm

6. *All data can be downloaded from http:\\ exact.iaps.inaf.it *Experimental CO2 absorption coefficients at high pressure and high temperature .S.Stefani et al (JQSRT, 2012) 1–28 http://dx.doi.org/10.1016/j.jqsrt.2012.11.019 **Thanks to this data now we have a theoretical model which reproduces our spectra better than 80% ** Measurements and modeling of high pressure pure CO2 spectra in central and wing regions from 600 to 9000 cm-1. H.Tran et al (JQSRT 2011) Absorbance(cm-1)

7. CO2 Collision Induced Absorption (CIA) p=40 bar

8. Study of the continuum Continuum: set of very weak absorption which consist of different effects, such as CIA, far wings, line mixing and so on. In order to distinguish each contribution it's necessary to work at high densities with very long optical paths. Our experimental setup does not allow to reach large optical path, because the gas cell is only 2 cm long. To overcome this limitation, the Cavity Ring Down (CRD) spectroscopy can be used

9. Venus’ atmospheric windows

10. Acousto optic switch DFB laser Beam splitter Optical isolator Cavity ring down apparatus Wavemeter, etalon Fotodiode Beam expander collimator Cavity ring down cell

11. Assembling the high pressure Cavity Ring Down cell Properties: Optical path 5.4 km; Volume : 3.8 L, Pressure rating 124 bar @ 37oC; 78 bar @ 200 oC

12. Laboratory measurements on CO2 [1] Loss rate = 1.93*10-6+1.17(5)*10-8 D+ 5.47(14)*10-10 D2 • We have three different contributions: • Constant due to the loss of the mirrors: 1.93*10-6 (cm-1) • Linear contribution due to Ryleigh scattering : • 1.17(5)*10-8 cm-1Amagat-1 (calculated 1.23(8)* 10-8 cm-1Amagat-1) • Quadratic contribution due tothe wings + CIA + continuum: • 5.47(14)*10-10 cm-1Amagat-2 • Refer to B. Bézard et al. (Icarus, 2011 and JOURNAL OF GEOPHYSICAL RESEARCH, 2009) • Continuum: 7(2)*10-10 cm-1Amagat-2 • Far wings: 2*10-10 cm-1Amagat-2 Quadratic fit [1] Carbon dioxide absorption at high densities in the 1.18 mm nightside transparency window of Venus M. Snels, S.Stefani, G.Piccioni and B. Bzard (Journal of Quantitative Spectroscopy and Radiative Transfer, 2013)

13. Multipass cell for FTIR • This apparatus is characterized by variable optical path from 2.5 up to 30 m, a pressure up to 10 bar and temperature from -30°C up to +100°C to study: • Collision induced absorption in CO2, H2 ecc. • Linebroadening in weak bands • Weak absorption features in planetary atmospheres (impurities, • less abundant isotopic species, gas mixtures, weak bands)

14. Multi pass gas cell @ intermediate pressure and high temperature Optical Layout Max path length: 30 m P.L. variable from 2.5 to 30 m Pressure From 1 to 10 bar Temperature From 200 to 400K

15. H2 @ room T 5 bar and 15m of Optical Path H2 @ room T 2 bar and 15m of Optical Path

16. Conclusions • The FTIR spectrometer in combination with heatable/coolable high pressure absorptioncellsallowsmeasurements for a large class of planetaryatmospherescovering a large spectralrange. • CRD is a powerfultechnique for studyingweakabsorptions in planetaryatmospheres up to high pressures and can be performedatdifferentwavelengths by usingnarrow band tunablelasers, which are availabethroughout the NIR. • Collisioninducedphenomena, important in high pressure atmospheres can be studied for pure gases and mixtures.