Laboratory Studies of Organic Chemistry in SpaceA. Ciaravella

Palermo, 2014 March 26

InterStellar Medium (ISM) overview ISM composition Dust and Ice Mantles : synthesis of complex moleculesLaboratory 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 regionsneutral hydrogen (HI) cloudsand 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 HIIonized ( UV radiation) − n ≈ 0.1 cm-3 − HII

Orion nebulaHubble 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

Large variety Diffuse, Giant, Dark, Dense cores T ≤ 10 − 50 K n 10≅ 2 – 104 cm-3

sizes 20-200 pc masses 103-107 M

mean density 102 cm-3

In cores (~1pc) n ~104 cm-3

Sites of chemical and dynamical activity leading to star formation H2 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

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

Where and in which conditions complex molecules can be produced?

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) !!!

Need for a heterogeneous chemistry

Chemistry in Dust Grain Mantles I

Dense (≥104 cm-3) and cold (10 – 20 K) regions

t ≤ 105 yr

Freeze-out time t ≈ 109/n [yr]

Diffuse ISM n ≈ 102 t ≈ 107 yr too long!!

Ice Mantles

Visible C18O N2H+

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, τq =4h/ΔE for H

✓thermal hopping, τh=ν-1exp(TB/T)reactions

diffusion

desorption

H2O

CH3OH

CO

NH3

CO2

Silicatecore

adsorption

CH3OH

CH4

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

1979 - UV irradiation ✓Hydrogen lamp 1216 Å 10.6 eV ✓T higher than today exp ✓6eV min E for breaking typical molecular bonds

~ 1983 - 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 CH3OH (Öberg et al 2009) UV NH3:CO

(Grim et al 1989)

46 MeV ions H2O:NH3:CO(Pilling et al. 2010)

A Typical Laboratory Setup

IR

Radiation Source

Mass S

pect,

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 SystemGas Line

Control System

Cold Finger

IR Spectrometer

Needle Valve Gas Inlet

Mass Spectrometer

UV Source ( HI Lyα )

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

!! 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

In the best case the density inside the chamber is: ≈ 1.3 × 106 particle cm-3 !!!

ISM gas is mainly H2 and CO

CO /H2 ≈ 10-6 − 10-4 Diffuse to Dense gas

Laboratory Vacuum Composition

H2

CO CO2

H2O

2 × 10-9 mbar

5.3 × 107 part. cm-3

1.5 × 10-10 mbar

4 × 106 part. cm-3

ISM CO /H2 ≈ 10-6 − 10-4

Laboratory vs ISM Conditions: II cont

Lab CO /H2 ≈ 0.4 − 0.5

H2O !!!

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 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

Molecular clouds are stable over time > 3 × 107 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 108 cm-2 s-1 Lab 1015 cm-2 s-1

103 yr 1 h

Molecular InfraRed Spectra

InfraRed spectra originate from molecules vibrational-rotational modes

105 104 103 102cm-1 101

λ = 2.5 × 10-3 cm = 400 cm-1

10-5 10-4 10-3 10-2cm 10-1

λ = 2.5 × 10-4 cm = 4000 cm-1

Ultraviolet Visible Near InfraRed Far Infrared Microwaves infrared

Near−IR: Overtone or Harmonic vibrationsMid−IR: Fundamental vibrationsFar−IR: Rotational Spectroscopy

ICES

Transmittance

Absorbance

InfraRed Spectra

Iλ(0) Iλ

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

TwistingAsymmetrical

Strecthing

RockingScissoring

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

Change in the dipole moment molecular IR band

CH2

InfraRed Spectra: II

Tra

smit

tanc

e %

Wavenumber (cm-1)

Functional Groups Molecular 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 Gudel 2003

X-ray irradiation of ICEs is a new research field

after Ribas et al. 2005

X-ray Interaction with the IceUV HI Lyα 10.9 eV interacts with molecular bonds

X-rays photons interact with the atoms of the molecules

KE = hν – BE Auger KE = EA- EB - EC

A=1s

B=2p1/2

C=2p3/2

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 2p1/2 2p3/2

8 O 532 24 7

2 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, 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

•Deposited CH3OH Ice @ 10 K

•Take a IR spectrum

IR

•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

•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

550 eV

Photon Flux ~ 4 × 1012 ph cm-2 s-1

lo

g(N

ph

cm-2 s

ec-1)

★

X-ray Irradiation of CH3OH Ice: contThe used flux ~ 4 × 1012 ph cm-2 s-1

is typical of a very active young solar type star

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

Ethanol

Glycolaldehyde

Formaldehyde

Acetic Acid

Methyl Fomate

Formic Acid

Methane

b blendedW weak

All de

tect

ed in

the I

SM

New Species: cont

Column densities increase with irradiation time (absorbed energy)

Heating the IceAfter 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 SpaceH2 C3 c-C3H C5 C5H C6H CH3C3N CH3C4H CH3C5N HC9N c-C6H6 HC11NAlF C2H l-C3H C4H l-H2C4 CH2CHCN HC(O)OCH3 CH3CH2CN (CH3)2CO CH3C6H C2H5OCH3  C60

AlCl C2O C3N C4Si C2H4 CH3C2H CH3COOH (CH3)2 O (CH2OH)2 C2H5OCHO n-C3H7CN C70

C2 C2S C3O l-C3H2 CH3CN HC5N C7H CH3CH2OH CH3CH2CHO CH3OC(O)CH3

CH CH2 C3S c-C3H2 CH3NC CH3CHO C6H2 HCNCH+ HCN C2H2 H2CCN CH3O CH3NH2 CH2OHCHO C8HCN HCO NH3 CH4 CH3SH c-C2H4O l-HC6H  CH3C(O)NH2

CO HCO+ HCCN HC3N HC3NH+ H2CCHOH CH2CHCHO C8HFCO+ HCS+ HCNH+ HC2NC HC2CHO C6H– CH2CCHCN C3H6

CP HOC+ HNCO HCOOH NH2CHO H2NCH2CNSiC H2O HNCS H2CNH C5N CH3CHNHHCl H2S HOCO+ H2C2O l-HC4H KCl HNC H2CO H2NCN l-HC4NNH HNO H2CN HNC3 c-H2C3ONO MgCN H2CS SiH4 H2CCNHNS MgNC H3O+ H2COH+ C5N–

NaCl N2H+ c-SiC3 C4H– HNCHCNOH N2O CH3 HC(O)CN PN NaCN C3N– HNCNHSO OCS PH3 CH3O SO+ SO2 HCNO NH4

± SiN c-SiC2 HOCN H2NCO±

SiO CO2 HSCNSiS NH2 H2O2

CS H3+ C3H±

HF SiCN HMgNCHD AlNCFeO SiNCO2 HCP CF+ CCP SiH AlOHPO H2O+AlO H2Cl±

OH+ KCN CN= FeCNSH± HO2

SH TiO2 HCl±

TiOArH±

≥ 75% contains CarbonThe interstellar chemistry is

carbon-dominated

Organic Molecules & Origin of Life on Earth

Our Solar System was born 4.6 × 109 yr

Life started on Earth3.6 × 109

3.8 × 109 End of impactsOnly 200 million yr !

Meteorites, comets etc etc bombardment

3.55 × 109 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(N2, CO, CO2 H2O) …… too rich of O

CH4, NH3, H2O, H2

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)

Laboratory UV irradiation of ice mixtures:

H2O:CH3OH:NH3:CO:CO2

glycine, serine, alanine,valine, aspartic acid, proline

(Muñ

oz-C

aro

et a

l 200

2)

(Ber

nste

in e

t al 2

002)

H2O:CH3OH:NH3: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 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