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Laboratory Studies of Organic Chemistry in Space A. Ciaravella Palermo, 2014 March 26 InterStellar Medium (ISM) overview ISM composition Dust and Ice Mantles : synthesis of complex molecules Laboratory Astrochemistry: main results Space vs Laboratory conditions IR Spectroscopy (Ices) An experiment step by step Synthesis of organic compounds on the origin of life InterStellar Medium (ISM) The ISM: ● mostly gas and dust existing over a wide range of physical conditions ● ● ● ● dust is 1% in mass half of the ISM mass in our Galaxy is composed by molecule processed by the radiation field from stars and cosmic rays Can be devided in 5 components: “coronal” gas warm intercloud medium HII regions neutral hydrogen (HI) clouds and complexes of giant molecular clouds (GMCs) ISM: Hot and Warm Gas Hot or Coronal gas T ≥ 106 k n ≤ 0.5 cm-3 Hot gases ejected in stellar explosions and winds Observed as ar-UV absorption lines of highly ionized atoms soft X-ray background VELA (0.1 - 2.4 keV), ROSAT Warm gas T ≤ 104 k 0.1 ≤ n ≤ 1 cm-3 The source in not entirely clear Can be neutral or ionized Observed as neutral − n ≈ 1 cm-3 − emission features in HI Ionized ( UV radiation) − n ≈ 0.1 cm-3 − HII Orion nebula Hubble Space Telescope Neutral Hydrogen Clouds Almost half of the ISM T < 102 K n ≈ 50 cm-3 Observed in neutral HI 21 cm line Excellent tracers of spiral structure Molecular Clouds Sites of chemical and dynamical activity leading to star formation H2 is the dominant molecule but CO is used to map the clouds Large variety Diffuse, Giant, Dark, Dense cores T ≤ 10 − 50 K n ≅ 102 – 104 cm-3 sizes 20-200 pc masses 103-107 M mean density 102 cm-3 In cores (~1pc) n ~104 cm-3 A Multi-Wavelenght View of the Milky Way Visible HI 21cm CO 115GHz H2 X-ray Dust extinction Dark regions ISM Composition Neutral Atoms: mainly H and He, with signicant amounts of C, N, O Ions: mainly H+ and cations of other abundant elements. Cations are the dominating ions in ISM Electrons: from ionization. Free electrons are signicantly abundant. Small Size Molecules: the most abundant are H2 and CO, but other small size are present, mainly in molecular clouds. Larger Molecules: mainly, polycyclic aromatic hydrocarbons PAH have been found in many places in galaxies. Dust Particles: small particles 0.01 − 1 μm Composition Si, Fe, C, and O Play a crucial role in the formation of molecules Molecular Clouds: the richest in molecules 1) Medium complexity molecules e. g. CO , NH3, H2O, HCnN (up to n=13) 2) Polycyclic Aromatic Hydrocarbons (PAH) , C C multiple bonds 3) Large partly H saturated molecules( with no C C multiple bonds & > 3 H) Which are the formation routes? 3-body no working in gas phase. 2-body efficient in gas phase for 1) and 2) No gas phase routes for 3) !!! Where and in which conditions complex molecules can be produced? Need for a heterogeneous chemistry Chemistry in Dust Grain Mantles I Dust grains have icy mantles t ≈ 109/n Freeze-out time Diffuse ISM n ≈ 102 t ≈ 107 yr Dense (≥104 cm-3) and cold (10 – 20 K) regions t≤ Visible 105 yr C18O [yr] too long!! Ice Mantles N 2 H+ Evidence for freeze out appear as emission holes in the maps of some molecules Chemistry in Dust Grain Mantles II Adsorption or sticking efficiency is high for dust grains. H adsorption CO O reactions CO2 Mobilty of particles is necessary for chemical reactions: ✓quantum tunneling, τq =4h/ΔE for H C Silicate core NH3 ✓thermal hopping, τh=ν-1exp(TB/T) diffusion H2O CH3OH CH4 desorption Desorption occurs continuously: ✗ Micro exothermic reaction liberates molecule from surface; ✗ Macro explosive liberation of molecules by mantle destruction by energetic photons or cosmic rays; ✗ Violent collective destruction of grains by shock waves Feeding the ISM From Prestellar through the collapsing envelope into a planetary disk Laboratory Astrochemistry: ICES The brightest UV line 1979 - UV irradiation ✓Hydrogen lamp 1216 Å ✓T higher than today exp ✓6eV min E for breaking 10.6 eV typical molecular bonds after Zombec handbook ~ 1983 - Particle bombardment Ion beam effects of sputtering and ionchemistry mediated by the solar wind and cosmic rays Sample Energies Few keV to hundred MeV Laboratory Astrochemistry: Results Many of the observed molecules have been produced in laboratory UV CH3OH UV NH3:CO (Öberg et al 2009) (Grim et al 1989) 46 MeV ions H2O:NH3:CO (Pilling et al. 2010) A Typical Laboratory Setup Mass Spect, Radiation Source IR 1 − A gas is deposited on a cold (≤ 15 K) InfraRed transparent substrate 2 − The ice is then irradiated 3 − Ice evolution is followed by means of IR spectroscopy (mostly transmission) 4 − After irradiation the substrate is heated at a rate of 1-2 K min-1 or slower 5 − The ice desorbs and the desorbed species are detected by the Mass Spectrometer 6 − Refractory residue on the substrate LIFE (Light Irradiation Facility for Exochemistry) UV Source ( HI Lyα ) Cold Finger IR Spectrometer Control Needle Valve System Gas Inlet Pumping System Gas Line Mass Spectrometer Laboratory vs ISM Conditions: I Temperature 4 - 10 K or higher Chamber pressure: early exp. ~ 10-7 mbar today exp. ~ 10-10 mbar ~ 5 × 10-11 mbar How many part. cm-3 in the chamber? At sea level ~1bar and Standard Temperature and Pressure (STP) we have In the best case the density inside the chamber is: ≈ 1.3 × 106 particle cm-3 !!! Laboratory vs ISM Conditions: II In the best case the density inside the chamber is: ≈ 1.3 × 106 particle cm-3 !!! !! MUCH MORE dense (> 104 times) than the average density in ISM This value is closer to: ✔ ✔ Dense cores in molecular clouds (where ices form!) Regions of stellar formations ISM gas is mainly H2 and CO CO /H2 ≈ 10-6 − 10-4 Diffuse to Dense gas Laboratory vs ISM Conditions: II cont ISM CO /H2 ≈ 10-6 − 10-4 Laboratory Vacuum Composition 2 × 10-9 mbar 5.3 × 107 part. cm-3 1.5 × 10-10 mbar 4 × 106 part. cm-3 H2O H2 CO CO2 Lab CO /H2 ≈ 0.4 − 0.5 H2O !!! Laboratory vs ISM Conditions: III As in the ISM particles in the chamber stick to the ice. Sticking coefficient S measures the capability of a given species to stick to a surface S = f (Surf. Cov, T, F, ….) 0 ≤ S≤ 1 The time required to accrete Assuming S=1 ~ 28 hours !! Coarse vacuum conditions high deposition of H2O on top of the ice Laboratory vs ISM Conditions: III cont Radiation fluxes in the lab are orders of magnitude larger than in the space ✖ even if compatible with stellar emission ✖ not much with the fluxes inside the clouds UV X Laboratory chemistry is quick! ✔ Irradiation times range from min to several hours ✔ The same absorbed energy/photon could take several yr ( or much more !!) in space UV space 6< F<2000 eV 108 cm-2 s-1 Lab 1015 cm-2 s-1 103 yr 1h Molecular clouds are stable over time > 3 × 107 yr Molecular InfraRed Spectra InfraRed spectra originate from molecules vibrational-rotational modes cm-1 105 Ultraviolet cm 10-5 104 Visible Near infrared 103 InfraRed 10-4 Far Infrared 10-3 λ = 2.5 × 10-4 cm = 4000 cm-1 101 102 Microwaves 10-2 λ = 2.5 × 10-3 cm = 400 cm-1 ICES Near−IR: Overtone or Harmonic vibrations Mid−IR: Fundamental vibrations Far−IR: Rotational Spectroscopy 10-1 d IR Source Iλ(0) InfraRed Spectra Iλ IR Detector Absorption/Transmission coupling of a dipole vibration with the electric field of the infrared radiation Transmittance Absorbance Optical depth molecule & line dependent Molecular Vibrational Spectra Change in the dipole moment molecular IR band Not all the molecules are IR active: H2, N2 are IR inactive CO2 linear molecule is IR inactive for symmetric stretch of the O atoms Symmetrical Strecthing Twisting Asymmetrical Strecthing CH2 Wagging Scissoring Rocking InfraRed Spectra: II The absorption due to a particular dipole oscillation is generally not affected greatly by other atoms present in the molecule. Trasmittance % The absorption occurs at ~ the same frequency for all bonds in different molecules. Functional Groups Molecular Fingerprints Wavenumber (cm-1) Bonds with H (vs C, O) higher energies InfraRed Spectra: III Absorption of C = O occurs always 1680 − 1750 cm-1 O−H “ “ “ 3400 − 3650 cm-1 C=C “ “ “ 1640 − 1680 cm-1 InfraRed Spectra: cont The Column Density molecular mass The ice tickness species density Avogadro number X-ray Irradiation of Ices X-ray irradiation of ICEs is a new research field Why X-ray Irradiation ? Almost all stars are X-ray emitters after Güdel 2003 Emission varies with age Young stars X-rays > EUV & vacuum UV X-rays penetrate deeply in circumstellar regions inhibited to EUV and UV after Ribas et al. 2005 X-ray Interaction with the Ice UV HI Lyα 10.9 eV interacts with molecular bonds X-rays photons interact with the atoms of the molecules ph 550 eV KE = hν – BE = 18 eV C=2p3/2 B=2p1/2 Auger KE = EA- EB - EC = 501 eV Z BE (eV) 1s 8O 532 2p1/2 2p3/2 24 7 A=1s 2 e- 18 & 501 eV hν < BE atom into an excited state accompained by single electron emission Interaction of ices with X-rays is a multistep process Ionization of the atoms in the molecule Production of secondary e- which in turn interact with the medium X-ray Irradiation of Ice 1) Irradiation of simple ices: CO, CO2, H2O, CH3OH study the products their dependence from physical parameter 2) Ice mixtures: H2O + CO + NH3, H2O + CH3OH +NH3 …. We will go Through an Experiment National Synchrotron Radiation Research Center (NSRRC-Taiwan) Irradiation of CH3OH ice with 550 eV photons X-ray Irradiation of CH3OH Ice •Deposited CH3OH Ice @ 10 K •Take a IR spectrum 550 eV Photon Flux ~ 4 × 1012 ph cm-2 s-1 •Compute the ice tickness using the 1026 cm-1 band •Compute the column density N = 2.08 × 1018 cm-2 nML= 2080 d = 1.08 μm X-ray Irradiation of CH3OH Ice: cont The used flux ~ 4 × 1012 ph cm-2 s-1 is typical of a very active young solar type star log(N ph cm-2 sec-1) ★ X-ray Irradiation of CH3OH Ice: cont 1) Start irradiation sequence @ 550 eV : 16, 80, 160,340, 640,960,1200….70m5s 2) Taking IR spectra after each step Many new features New Species Formic Acid Acetic Acid Glycolaldehyde Methane Formaldehyde Methyl Fomate Ethanol b W blended weak New Species: cont Column densities increase with irradiation time (absorbed energy) Heating the Ice After irradiation the CH3OH ice is heated at a rate of 1 K/min T T CH3OH start desorbing at ~120 K Residue A refractory residue left on the substrate X-rays vs Particle & UV X-ray Products of irradiation are more similar to e− More efficient than e− and UV HCOOCH3 ≈ 10 times more than e− HCOOCH3 not a product of UV × a Bennet et al. 2007 b Öberg et al 2009 An Inventory of Molecules in Space H2 C3 AlF C2H AlCl C2O C2 C2S CH CH2 CH+ HCN CN HCO CO HCO+ CO+ HCS+ CP HOC+ SiC H2O HCl H2S KCl HNC NH HNO NO MgCN NS MgNC NaCl N2H+ OH N2O PN NaCN SO OCS SO+ SO2 SiN c-SiC2 SiO CO2 SiS NH2 CS H3+ HF SiCN HD AlNC FeO SiNC O2 HCP CF+ CCP SiH AlOH PO H2O+ AlO H2Cl± OH+ KCN CN= FeCN SH± HO2 SH TiO2 HCl± TiO ArH± c-C3H C5 l-C3H C4H C3N C4Si C3O l-C3H2 C3S c-C3H2 C2H2 H2CCN NH3 CH4 HCCN HC3N HCNH+ HC2NC HNCO HCOOH HNCS H2CNH HOCO+ H2C2O H2CO H2NCN H2CN HNC3 H2CS SiH4 H3O+ H2COH+ c-SiC3 C4H– CH3 HC(O)CN C3N– HNCNH PH3 CH3O HCNO NH4± HOCN H2NCO± HSCN H2O2 C3H± HMgNC C5H C6H CH3C3N CH3C4H CH3C5N l-H2C4 CH2CHCN HC(O)OCH3 CH3CH2CN (CH3)2CO C2H4 CH3C2H CH3COOH (CH3)2 O (CH2OH)2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH3NC CH3CHO C6H2 HCN CH3O CH3NH2 CH2OHCHO C8H CH3SH c-C2H4O l-HC6H CH3C(O)NH2 HC3NH+ H2CCHOH CH2CHCHO C8HF HC2CHO C6H– CH2CCHCN C3H6 NH2CHO H2NCH2CN C5N CH3CHNH l-HC4H l-HC4N c-H2C3O H2CCNH C5N– HNCHCN HC9N c-C6H6 CH3C6H C2H5OCH3 C2H5OCHO n-C3H7CN CH3OC(O)CH3 HC11N C60 C70 ≥ 75% contains Carbon The interstellar chemistry is carbon-dominated Organic Molecules & Origin of Life on Earth 4.6 × 109 yr 3.8 × 109 3.6 × 109 Our Solar System was born Meteorites, comets etc etc bombardment End of impacts Only 200 million yr ! Life started on Earth 3.55 × 109 yr old fossilized microorganisms (< 10 μm) from the Barberton Greenstone Belt (South Africa). … if (& oh what a big if) we could conceive in some warm little pond with all sorts of ammonia & phosphoric salts,—light, heat, electricity……a protein compound was chemically formed ….(Charles Darwin, 1 Feb 1871, letter to J.D. Hooker) 1953: Miller Experiment CH4, NH3, H2O, H2 Earth atmosphere composition(N2, CO, CO2 H2O) …… too rich of O Amino Acids in Space ? To date amino acids have not been detected in the Interstellar Medium. 1999: NASA’s Stardust (http://stardustnext.jpl.nasa.gov) Glycine detection in a samples from comet 81P/Wild 2 (Elsila et al 2009) (Muñoz-Caro et al 2002) Laboratory UV irradiation of ice mixtures: H2O:CH3OH:NH3:CO:CO2 H2O:CH3OH:NH3:HCN glycine, serine, alanine, (Bernstein et al 2002) glycine, serine, alanine,valine, aspartic acid, proline Amino Acids in Space ? cont Many Complex molecules in Space are Prebiotic (i.e. with structural elements in common with those found in living organisms) ➛ 2002 Hydrogenated sugar, ethylene glycol HOCH2CH2OH ➛ 2004 Interstellar sugar, glycolaldehyde CH2OHCHO ➛ 2006 The largest interstellar molecule with a peptide bond, Acetamide, CH3CONH2 ➛ 2008 A direct precursor of the amino acid glycine, amino acetonitrile NH2CH2CN It is likely that life is a common phenomenon throughout our Universe