Spectroscopy of complex organic molecules on Titan A. JOLLY

Spectroscopy of complex organic molecules on Titan A. JOLLY

Outline of the talk New molecules on Titan? Expected molecules from laboratory experiment Results from the Huygens lander Infrared observation from CIRS-CASSINI Improvement in infrared spectroscopy Ultraviolet observation from UVIS-CASSINI Improvement in ultraviolet spectroscopy

Past IR observations of TITAN

Species Abundances Predominant species N 2 0.85 0.98 CH 4 5.10-3 8,5.10-2 Hydrocarbons C 2 H 6 7.10-6 2,8.10-5 C 2 H 2 1,65.10-6 3,8.10-6 C 3 H 8 3.10-7 1.10-6 C 2 H 4 7.10-8 2.10-7 C 3 H 4 (propyne) 4.10-9 8,5.10-9 C 4 H 2 8.10-10 -2.10-9 C 3 H 4 (allene) < 10-9 C 6 H 6 1.10-10 -7.10-10 C 6 H 2? Titan s atmosphere Nitriles HCN 1.10-7 4.10-7 HC 3 N 8. 10-10 8,4.10-8 CH 3 CN 1,5.10-9 10-8 C 2 N 2 some 10-9 C 4 N 2 solid HC 5 N? Oxygenated compounds CO 3,3.10-6 6,4.10-5 CO 2 9.10-9 2,2.10-8 H 2 O 8.10-9

Titan s Atmospheric chemistry Long UV short UV CH 4 N 2 C 2 H 4 HCN C 2 H 2 CH 3 CN CH 3 CCH HC 3 N C 2 H 6 C 4 H 2 C 2 N 2 C 3 H 8 condensation sedimentatio n

Dust formation on TITAN and in the laboratory? Organic particles are easily formed in a N 2 /CH 4 plasma Caracteristics : molecules formed (all molecules detected on Titan and more) Refraction Index (compared to Titan s albedo) Chemical composition (C/N ratio) UV emission Spectroscopic analysis (radicals ; CN, NH, CH...)...

IR spectrum of a mixture produced by a N2/CH4 plasma discharge

Huygens Atmosphérique Entry: 14-01-2005

Huygens GC-MS data

Cassini at Saturn since 1. July 2004

INMS

CIRS Observations of Titan : various latitudes

CIRS Observations of Titan : north to south ratio

CASSINI MISSION Composite InfraRed Spectrometer

C 6 H 2? TITAN Limb Observation (CIRS) T = 100 K 0.15 0.10 C 4 H 2 HC 3 N HC 5 N? CO 2 HCN C 2 H 2 Obs Sim Flux 0.05 0.00 C 3 H 4-0.05-0.10 600 620 640 660 680 700 720 740 760 780 800 cm -1

HC 3 N in Titan. Hot bands? 20000 HC 3 N Titan North Limb (180 km)? 0 640 645 650 655 660 665 670 675 680 cm -1

Infrared Spectra of HC 3 N (resolution : 0.5 cm -1 ) 1.2 1.0 Exp G E IS A Absorbance 0.8 0.6 0.4 0.2 0.0 1.2640 650 660 670 680 690 Absorbance 1.0 0.8 0.6 0.4 ν 5 Exp This work 0.2 ν 5 -> 2ν 5 (Π - Σ ) ν 5 -> 2ν 5 (Π - ) 0.0 640 650 660 670 680 690 W avenumber (cm -1 )

Energy level diagram : HC 3 N Hot bands in HC 3 N 2ν 5 Σ + + Σ + +Σ + ν 5 +ν 6 ν 5 +2ν 7 Π+Φ 33 % of the population in the ground level at room T Σ + + Π+Φ 2ν 6 ν 6 +2ν 7 ν 5 +ν 7 Σ + +Σ + Σ + +Σ + ν 6 +ν 7 ν 5 Π Π ν 6 2ν 7 Σ + + ν 7 Π Ground Σ +

Fayt et al. (2000) 181 sublevels between 0 and 1750 cm-1 2000 calculation by Fayt experiment 1500 abs. coeff 1000 500 0 640 645 650 655 660 665 670 675 680 685 690 cm -1

Hot HC 3 N bands in Titan 20000 15000 HC 3 N Fayt 300 K Fayt 100 K Titan North Limb (180 km) 10000 5000 0 640 645 650 655 660 665 670 675 680

More hot bands on Titan? YES 30000 CIRS LIMB Observation of Titan Simulation with GEISA @ 300 K C 4 H 2 20000 Flux 10000 C3H4 0 620 622 624 626 628 630 632 634 636 638 640 cm -1

C 4 H 2 simulation 10000 8000 6000 4000 2000 0 600 610 620 630 640 650

First absolute intensity measurement for HC 5 N in the infrared (resolution : 0.5 cm -1 ) 100 90 ν 7 80 Abs. Coeff. (cm -1.atm -1 ) 70 60 50 40 30 20 10 ν 8 ν 8 +ν 11? ν 9 +ν 10? 0 450 500 550 600 650 700 750 Wavenumber (cm -1 )

Comparison with theoretical results HC 5 N Absolute Intensities (atm -1 cm -2 ) at 296 K Mode Vibration Position (cm -1 ) This work (2005) Theoretical Results* ν 1 /ν 3 +ν 5 C-H str. (R) 3333 (P) 3322 167 508 a /362 b ν 2 C=C str. (R) 2257 (P) 2248 77.6 277 a /138 b ν 3 C=C str. (R) 2192.5 (P) 2182.5 17.3 1.24 a /22.5 b ν 7 bend. 642.2 128.3 177 a /318 c ν 8 bend. 500.9 10 7.4 a /55 c * converted from km/mol to atm -1.cm -2 a Scemama (2002) b Botschwina (1997) c Deguchi (1984), Uyemura (1986)

CASSINI UVIS Team, Science (2005)

Experimental study done at BESSY : Berlin Synchrotron Facility (GERMANY) April and July 2005 HC 3 N absorption spectra depending on the Temperature 4000 295 K 220 K 3000 relative intensity 2000 1000 0 121,5 122,0 122,5 123,0 Wavelength (nm)

Cyanopolyynes spectra above 120 nm, HCN.. 1600 Absorption coefficient (cm -1.amagat -1 ) 1400 1200 1000 800 600 400 200 0 120 125 130 135 140 145 150 155 160 Wavelength (nm)

Cyanopolyynes spectra, HCN, HC3N.. Absorption coefficient (cm -1.amagat -1 ) 5000 4000 3000 2000 1000 0 HCN HC 3 N 120 125 130 135 140 145 150 155 160 Wavelength (nm)

Cyanopolyynes spectra, HCN, HC3N, HC5N.. Absorption coefficient (cm -1.amagat -1 ) 8000 7000 6000 5000 4000 3000 2000 1000 HCN HC3N HC5N 0 120 140 160 180 200 Wavelength (nm)

New C4H2 spectra and UVIS occultation spectra

Simplified photochemical model : polymerisation Reactions with radicals H + CH C H + H HC N+ CH HC N+ H 2n 2 2 + 2n + 1 2 2n+ 3 C 2(n 1) 2 Photodissociation : C 1 H + CN HC N+ H 2n 2 2n+ C H + hν C H+ H 2n 2 2n Photodissociation rates: Φ( λ) S( λ) τ ( z) σ ( λ,t ) J= Quantum yield λ0 0 φ Solar Flux (photons.cm -2.s -1 ) Optical depth Absorption cross Section HC N+ hν C N+ H 2n + 1 2n+ 1 ( ) ( ) τ ( z) λ. S λ. e. σ( λ, T). dλ

Solar spectrum in the absorption domain of hydrocarbons and nitriles Solar Spectrum 1E10 1E9 1E8 Flux photon/s/cm2 1E7 120 130 140 150 160 170 180 190 200 Wavelength (nm)

Predicted relative abondance of polyynes and cyanopolyynes on Titan 1 HCN C 2 H 2 Cyanopolyynes Polyynes Abondance relative 0.1 0.01 HC 3 N C 4 H 2 C 6 H 2 1E-3 HC 5 N 0 1 2 3 4 5 6 7 Nombre de Carbone

CRL 618 : Nebuleuse proto-planétaire riche en carbone

Predicted relative abondance of polyynes on Titan and CRL618 1 C 2 H 2 TITAN CRL 618 Abondance relative 0.1 C 4 H 2 C 6 H 2 0.01 1 2 3 4 5 6 7 Nombre de Carbone

ISO Observation of CRL 618 Observations 1.1 Spectra calculation 1.0 0.9 Transmission 0.8 0.7 0.6 C 6 H 2 C 4 H 2 HCN 0.5 0.4 C 6 H 2 /C 4 H 2 = 0.6 C 2 H 2 0.3 620 680 700 720 740 760 780 Wavenumber (cm -1 )

Predicted relative abondance of cyanopolyynes on Titan and CRL618 1 HCN TITAN CRL 618 Abondance relative 0.1 0.01 HC 3 N HC 5 N 1E-3 0 1 2 3 4 5 6 7 Nombre de Carbone

1,2 1,1 ISO Observation of CRL618 Obs Sim 1,0 0,9 HC 5 N Flux 0,8 0,7 0,6 C 6 H 2 C 4 H 2 HC 3 N HCN 0,5 0,4 0,3 C 2 H 2 620 640 660 680 700 720 740 760 780 cm -1

Titan's spectroscopic database http://www.lisa.univ-paris12.fr/gpcos/scoopweb/scoop.html The LISA Team and collaborators UV spectroscopy Titan's spectroscopic :Yves Benilan database, Thomas Ferradaz, Martin Schwell, Marie-Claire Gazeau, Nicolas Fray, Hans Jochims (Berlin) IR spectroscopy : Yves Benilan, Jean Claude Guillemin (Rennes), André Fayt (Louvain la neuve)