Formation of Astrobiologically Important Molecules in Extraterrestrial Environments

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Formation of Astrobiologically Important
Molecules in Extraterrestrial Environments
Ralf I. Kaiser Department of Chemistry University
of Hawaii Honolulu, HI 96822 kaiser_at_gold.chem.haw
aii.edu http//www.chem.hawaii.edu/Bil301/welcome.
html
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Orion Constellation
Orion Nebula
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Interstellar Medium

molecular clouds and cores
e
s


circumstellar envelopes

T 10 K r 10-11 cm-3
T 10 4000 K r 102 109 cm-3

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Amino Acid
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Characteristics of a Chemical Reaction
1. exoergic vs. endoergic 2. no entrance barrier
vs. barrier 3. binary vs. ternary reactions
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The 70es Bimolecular Ion-Molecule Reactions
O O e-
O H2 OH H
OH H2 OH2 H
OH2 H2 OH3 H
OH3 e- H2O H
simple hydrides in cold molecular clouds (CH4,
NH3, H2O)
k 10-9 cm3s-1 (Herbst et. al)
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The 80es Problems with Ion-Molecule Reactions
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The 80es Problems with Ion-Molecule Reactions
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The 90es Bimolecular Neutral-Neutral Reactions
CN(X2?) CnHm CnH(m-1)CN H
C2H(X2?) CnHm CnH(m-1)C2H H
C(3Pj) CnHm C(n1)H(m-1) H
C2(X1?g) CnHm C(n2)H(m-1) H
k 10-10 cm3s-1 (Kaiser et al. Smith et al.)
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The 90es Bimolecular Neutral-Neutral Reactions
IRC10216
Titan
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Interstellar Medium

molecular clouds and cores
e
s


circumstellar envelopes

T 10 K r 10-11 cm-3
T 10 4000 K r 102 109 cm-3

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Cold Molecular Cloud B68
cosmic ray particles
UV photons
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water
carbon monoxide
carbon dioxide
methane
ammonia
methanol
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The late 90es Grain-Surface Reactions
H H H2
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water
carbon dioxide
carbon monoxide
methane
ammonia
methanol
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The 00es - Galactic Cosmic Ray Processing
9 MeV
electronic interaction

• ionization
• 2. electronic excitation
• 3. vibrational excitation
• 4. electron attachment

10 MeV
cleavage of chemical bonds
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The 00es - Galactic Cosmic Ray Processing
1. Energy Conservation
10 eV transfer 4.5 eV bond energy 5.5 eV
maximum kinetic energy
2. Angular Momentum Conservation
H atom (5.15 eV) versus CH3 radical (0.35 eV)
kinetic energy
vibrational energy
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Non-Equilibrium Chemistry
A BC
1. exoergic vs. endoergic 2. no entrance barrier
vs. barrier 3. binary vs. ternary reactions
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C2H4O Isomers
ethylene oxide
vinyl alcohol
acetaldehyde
H2O, CO, CO2, NH3, CH4, CH3OH
CO2/C2H4
CO/CH4
H2O/C2H2
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C2H4O Isomers
ethylene oxide
vinyl alcohol
acetaldehyde
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Surface Scattering Machine
p 8?10-11 torr
T 10 350 K
LET (5 keV e-) 3 5 keV ?m-1 LET (10 MeV H)
30 min laboratory 106 years in cold molecular
cloud
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Sources

1. electron source

2. cation source (positively charged particles)
3. pyrolytic radical source
4. tunable photon source
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CO/CH4 Ice before Irradiation at 10 K
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CO/CH4 Ice after Irradiation at 10 K
612 cm-1 ?2 (CH3 out of plane)
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CO/CH4 Ice after Irradiation at 10 K
1853 cm-1 ?3 (HCO CO stretch)
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CO/CH4 Ice after Irradiation at 10 K
1725 cm-1 ?4 (CH3CHO CO stretch)
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QMS CO/CH4 during Irradiation
H H H2
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CO/CH4 Ices after Irradiation at 10 K
CH4-CO CH3HCO CH3CHO
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Kinetics
(pseudo) 1st order kinetics
electron induced decomposition
CH4-CO CH3HCO CH3CHO
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Kinetics
k1
k2
CH4-CO CH3HCO CH3CHO
a 2.32 (?0.42) ? 1015 cm-2 k1ltltk2 1.13 (?
0.29) ? 10-11 s-1
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Kinetics
k3
k4
CH4 (X1A1) CH3(X2A2) H(2S1/2)
CO (X1S) H(2S1/2) HCO (X2A)
a 3.39 (?0.15) ? 1015 cm-2 k4 5.49 (? 0.73)
? 10-11 s-1
a 3.87 (?0.18) ? 1015 cm-2 k3 4.4 (? 0.37) ?
10-11 s-1
CH4-CO CH3HCO CH3CHO
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Electronic Structure Calculations
Osamura et al. 2004
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C2H4O Isomers
ethylene oxide
vinyl alcohol
acetaldehyde
H2O, CO, CO2, NH3, CH4, CH3OH
CO2/C2H4
CO/CH4
H2O/C2H2
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CO2/C2H4 Ices after Irradiation at 10 K
2139 cm-1 ?1 (CO stretch)
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CO2/C2H4 Ices after Irradiation at 10 K
1723 cm-1 ?4 (CH3CHO CO stretch)
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CO2/C2H4 Ices after Irradiation at 10 K
868 cm-1 ?12 (c-C2H4O ring)
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Kinetics
(pseudo) 1st order kinetics
electron induced decomposition
C2H4-CO2 C2H4OCO C2H4OCO
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Kinetics
k1
k2
C2H4 O c-C2H4O
C2H4 O CH3CHO
a 2.10 (?0.09) ? 1015 cm-2 k1 5.22 (? 0.37) ?
10-12 s-1
a 1.77 (?0.05) ? 1015 cm-2 k2 6.29 (? 0.34)
? 10-12 s-1
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Mechanism
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Mechanism
cone of acceptance favors attack of ? bond
(formation of acetaldehyde and ethylene oxide)
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Mechanisms
CH4-CO CH3HCO CH3CHO
a 2.32 (?0.42) ? 1015 cm-2 k 1.13 (? 0.29) ?
10-11 s-1
C2H4-CO2 C2H4OCO C2H4OCO
a 2.10 (?0.09) ? 1015 cm-2 k 5.22 (? 0.37) ?
10-12 s-1
a 1.77 (?0.05) ? 1015 cm-2 k 6.29 (? 0.34) ?
10-12 s-1
CH3CHO
c-C2H4O
kinetics versus dynamics
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C2H4O Isomers
ethylene oxide
vinyl alcohol
acetaldehyde
H2O, CO, CO2, NH3, CH4, CH3OH
H2O/C2H2
CO/CH4
CO2/C2H4
synchrotron irradiations are crucial to
discriminate between O(3P) and O(1D)
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Interstellar Medium

molecular clouds and cores
e
s


circumstellar envelopes

T 10 K r 10-11 cm-3
T 10 4000 K r 102 109 cm-3

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Crossed Molecular Beams Machine
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Acknowledgements
Chris Bennett (UH, USA) Corey Jamieson (UH,
USA) Prof. Nigel Mason (OU, UK) Prof. Yoshihiro
Osamura (Tokyo, Japan)