Transcript Laboratory Studies of Organic Chemistry in Space A. Ciaravella

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