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 ≥ 10 6 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 ( keV), ROSAT  Warm gas T ≤ 10 4 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 < 10 2 K n ≈ 50 cm -3 Observed in neutral HI 21 cm line Excellent tracers of spiral structure

Molecular Clouds Large variety Diffuse, Giant, Dark, Dense cores T ≤ 10 − 50 K n ≅ 10 2 – 10 4 cm -3 sizes pc masses M  mean density 10 2 cm -3 In cores (~1pc) n ~10 4 cm -3 Sites of chemical and dynamical activity leading to star formation H 2 is the dominant molecule but CO is used to map the clouds

A Multi-Wavelenght View of the Milky Way Visible HI 21cm CO 115GHz H 2 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 H 2 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 Where and in which conditions complex molecules can be produced? 1) Medium complexity molecules e. g. CO, NH 3, H 2 O, HC n N (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) !!! Need for a heterogeneous chemistry

Chemistry in Dust Grain Mantles I Dense (≥10 4 cm -3 ) and cold (10 – 20 K) regions t ≤ 10 5 yr Freeze-out time t ≈ 10 9 /n [yr] Diffuse ISM n ≈ 10 2 t ≈ 10 7 yr too long!! Ice Mantles Visible C 18 O N 2 H + Evidence for freeze out appear as emission holes in the maps of some molecules Dust grains have icy mantles

Chemistry in Dust Grain Mantles II Mobilty of particles is necessary for chemical reactions: ✓ quantum tunneling, τ q =4h/ΔE for H ✓ thermal hopping, τ h =ν -1 exp(T B /T) reactions diffusion desorption H2OH2O CH 3 OH CO NH 3 CO 2 Silicate core adsorption CH 3 OH CH 4 C O H Adsorption or sticking efficiency is high for dust grains. 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  UV irradiation ✓ Hydrogen lamp 1216 Å 10.6 eV ✓ T higher than today exp ✓ 6eV min E for breaking typical molecular bonds  ~ Particle bombardment effects of sputtering and ionchemistry mediated by the solar wind and cosmic rays Energies Few keV to hundred MeV Ion beam Sample after Zombec handbook The brightest UV line

Many of the observed molecules have been produced in laboratory Laboratory Astrochemistry: Results UV CH 3 OH (Öberg et al 2009) UV NH 3 :CO (Grim et al 1989) 46 MeV ions H 2 O:NH 3 :CO (Pilling et al. 2010)

A Typical Laboratory Setup IR Radiation Source Mass Spect, Gas Inlet 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) Pumping System Gas Line Control System Cold Finger IR Spectrometer Needle Valve Gas Inlet Mass Spectrometer UV Source ( HI Lyα )

Laboratory vs ISM Conditions: I Temperature K or higher Chamber pressure: early exp. ~ mbar today exp. ~ mbar ~ 5 × 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 × 10 6 particle cm -3 !!!

Laboratory vs ISM Conditions: II !! MUCH MORE dense (> 10 4 times) than the average density in ISM This value is closer to: ✔ Dense cores in molecular clouds (where ices form!) ✔ Regions of stellar formations In the best case the density inside the chamber is: ≈ 1.3 × 10 6 particle cm -3 !!! ISM gas is mainly H 2 and CO CO /H 2 ≈ − Diffuse to Dense gas

Laboratory Vacuum Composition H2H2 CO CO 2 H2OH2O 2 × mbar 5.3 × 10 7 part. cm × mbar 4 × 10 6 part. cm -3 ISM CO /H 2 ≈ − Laboratory vs ISM Conditions: II cont Lab CO /H 2 ≈ 0.4 − 0.5 H 2 O !!!

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 Laboratory vs ISM Conditions: III 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 H 2 O 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 Molecular clouds are stable over time > 3 × 10 7 yr 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 10 8 cm -2 s -1 Lab cm -2 s yr 1 h

Molecular InfraRed Spectra InfraRed spectra originate from molecules vibrational-rotational modes cm λ = 2.5 × cm = 400 cm cm λ = 2.5 × cm = 4000 cm -1 Ultraviolet Visible Near InfraRed Far Infrared Microwaves infrared Near−IR: Overtone or Harmonic vibrations Mid−IR: Fundamental vibrations Far−IR: Rotational Spectroscopy ICES

Transmittance Absorbance InfraRed Spectra I λ (0) IλIλ IR Source IR Detector molecule & line dependent d Absorption/Transmission coupling of a dipole vibration with the electric field of the infrared radiation Optical depth

Molecular Vibrational Spectra Symmetrical Strecthing Wagging Twisting Asymmetrical Strecthing RockingScissoring Not all the molecules are IR active:  H 2, N 2 are IR inactive  CO 2 linear molecule is IR inactive for symmetric stretch of the O atoms Change in the dipole moment molecular IR band CH 2

InfraRed Spectra: II Trasmittance % Wavenumber (cm -1 ) Functional GroupsMolecular Fingerprints The absorption due to a particular dipole oscillation is generally not affected greatly by other atoms present in the molecule. The absorption occurs at ~ the same frequency for all bonds in different molecules. 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 The ice tickness Avogadro number molecular mass species density

X-ray Irradiation of Ices Why X-ray Irradiation ? Almost all stars are X-ray emitters Emission varies with age Young stars X-rays > EUV & vacuum UV X-rays penetrate deeply in circumstellar regions inhibited to EUV and UV after Gu ̈ del 2003 X-ray irradiation of ICEs is a new research field after Ribas et al 

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 KE = hν – BE Auger KE = E A - E B - E C A=1s B=2p 1/2 C=2p 3/2  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 Z BE (eV) 1s 2p 1/2 2p 3/2 8 O e - 18 & 501 eV ph 550 eV = 18 eV = 501 eV hν < BE atom into an excited state accompained by single electron emission

X-ray Irradiation of Ice 1) Irradiation of simple ices: CO, CO 2, H 2 O, CH 3 OH study the products their dependence from physical parameter 2) Ice mixtures: H 2 O + CO + NH 3, H 2 O + CH 3 OH +NH 3 …. 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 CH 3 OH Ice Deposited CH 3 OH 10 K Take a IR spectrum Deposited CH 3 OH 10 K Take a IR spectrum IR Compute the ice tickness using the 1026 cm -1 band Compute the column density N = 2.08 × cm -2 n ML = 2080 d = 1.08 μm Compute the ice tickness using the 1026 cm -1 band Compute the column density N = 2.08 × cm -2 n ML = 2080 d = 1.08 μm 550 eV Photon Flux ~ 4 × ph cm -2 s -1

log(N ph cm -2 sec -1 ) ★ X-ray Irradiation of CH 3 OH Ice: cont The used flux ~ 4 × ph cm -2 s -1 is typical of a very active young solar type star

X-ray Irradiation of CH 3 OH Ice: cont 1) Start irradiation 550 eV : 16, 80, 160,340, 640,960,1200….70 m 5 s 2) Taking IR spectra after each step Many new features

New Species Ethanol Glycolaldehyde Formaldehyde Acetic Acid Methyl Fomate Formic Acid Methane b blended W weak All detected in the ISM

New Species: cont Column densities increase with irradiation time (absorbed energy)

Heating the Ice After irradiation the CH 3 OH ice is heated at a rate of 1 K/min T T CH 3 OH 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  HCOOCH 3 ≈ 10 times more than e − HCOOCH 3 not a product of UV a Bennet et al b Öberg et al 2009

An Inventory of Molecules in Space H 2 C 3 c-C 3 H C 5 C 5 H C 6 H CH 3 C 3 N CH 3 C 4 H CH 3 C 5 N HC 9 N c-C 6 H 6 HC 11 N AlF C 2 H l-C 3 H C 4 H l-H 2 C 4 CH 2 CHCN HC(O)OCH 3 CH 3 CH 2 CN (CH 3 ) 2 CO CH 3 C 6 H C 2 H 5 OCH 3 C 60 AlCl C 2 O C 3 N C 4 Si C 2 H 4 CH 3 C 2 H CH 3 COOH (CH 3 ) 2 O (CH 2 OH) 2 C 2 H 5 OCHO n-C 3 H 7 CN C 70 C 2 C 2 S C 3 O l-C 3 H 2 CH 3 CN HC 5 N C 7 H CH 3 CH 2 OH CH 3 CH 2 CHO CH 3 OC(O)CH 3 CH CH 2 C 3 S c-C 3 H 2 CH 3 NC CH 3 CHO C 6 H 2 HCN CH + HCN C 2 H 2 H 2 CCN CH 3 O CH 3 NH 2 CH 2 OHCHO C 8 H CN HCO NH 3 CH 4 CH 3 SH c-C 2 H 4 O l-HC 6 H CH 3 C(O)NH 2 CO HCO+ HCCN HC 3 N HC 3 NH + H 2 CCHOH CH 2 CHCHO C 8 HF CO + HCS + HCNH + HC 2 NC HC 2 CHO C 6 H – CH 2 CCHCN C 3 H 6 CP HOC + HNCO HCOOH NH 2 CHO H 2 NCH 2 CN SiC H 2 O HNCS H 2 CNH C 5 N CH 3 CHNH HCl H 2 S HOCO + H 2 C 2 O l-HC 4 H KCl HNC H 2 CO H 2 NCN l-HC 4 N NH HNO H 2 CN HNC 3 c-H 2 C 3 O NO MgCN H 2 CS SiH 4 H 2 CCNH NS MgNC H 3 O + H 2 COH + C 5 N – NaCl N 2 H + c-SiC 3 C 4 H – HNCHCN OH N 2 O CH 3 HC(O)CN PN NaCN C 3 N – HNCNH SO OCS PH 3 CH 3 O SO + SO 2 HCNO NH 4 ± SiN c-SiC 2 HOCN H 2 NCO ± SiO CO 2 HSCN SiS NH 2 H 2 O 2 CS H 3 + C 3 H ± HF SiCN HMgNC HD AlNC FeO SiNC O2 HCP CF+ CCP SiH AlOH PO H 2 O+ AlO H 2 Cl ± OH+ KCN CN = FeCN SH ± HO 2 SH TiO 2 HCl ± TiO ArH ± ≥ 75% contains Carbon The interstellar chemistry is carbon-dominated

Organic Molecules & Origin of Life on Earth Our Solar System was born 4.6 × 10 9 yr Life started on Earth 3.6 × × 10 9 End of impacts Only 200 million yr ! Meteorites, comets etc etc bombardment 3.55 × 10 9 yr old fossilized microorganisms (< 10 μm) from the Barberton Greenstone Belt (South Africa). CONDITIONS NOT CONDUCIVE TO LIFE

1953: Miller Experiment … 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 ) Earth atmosphere composition(N 2, CO, CO 2 H 2 O) …… too rich of O CH 4, NH 3, H 2 O, H 2

Amino Acids in Space ? To date amino acids have not been detected in the Interstellar Medium. 1999: NASA’s Stardust ( ) Glycine detection in a samples from comet 81P/Wild 2 (Elsila et al 2009) Laboratory UV irradiation of ice mixtures: H 2 O:CH 3 OH:NH 3 :CO:CO 2  glycine, serine, alanine,valine, aspartic acid, proline (Muñoz-Caro et al 2002) (Bernstein et al 2002) H 2 O:CH 3 OH:NH 3 :HCN  glycine, serine, alanine,

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) It is likely that life is a common phenomenon throughout our Universe ➛ 2002 Hydrogenated sugar, ethylene glycol HOCH 2 CH 2 OH ➛ 2004 Interstellar sugar, glycolaldehyde CH 2 OHCHO ➛ 2006 The largest interstellar molecule with a peptide bond, Acetamide, CH 3 CONH 2 ➛ 2008 A direct precursor of the amino acid glycine, amino acetonitrile NH 2 CH 2 CN