Synthesis of Organic Compounds in Triple- reaction the Late Stages - - PDF document

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Synthesis of Organic Compounds in the Late Stages of Stellar Evolution

Sun Kwok

International conference on interstellar dust, molecules, and chemistry Pune, November 22, 2011

Evolution of intermediate mass (1-8 M⊙) stars

• Triple- reaction

(HeC)

• Slow neutron

capture (s-process)

(Y, Zr, Ba, La, Ce, Pr, Nd, Sm, Eu, etc)

• Thermal pulse and

dredge up

3 M⊙ track

0.1 1.0 10.0 100.0

Wavelength (m)

1 10 100

F(10-10 erg cm-2s-1 )

21318+5631

2500 BB LWS SWS

Model

Remnant AGB dust envelope in PN

1 10 100

Wavelength (m)

1 10 100 1000 10000

Flux (10-10 erg s-1 cm-2) BD +30 3639

In young PN, ~1/3 of flux emitted in IR (Zhang & Kwok 1991)

Dust continuum b-f continuum

Amorphous Silicates & silicon carbide

6 8 10 12 14 16 18 20 22 24

Wavelength (m)

1000 2000 3000 4000 5000 6000

F(10-10erg cm-2 s-1)

AFGL 5357 TX Cam

IRAS LRS 6 8 10 12 14 16 18 20 22 24

Wavelength (m)

200 400 600 800 1000 1200 1400 1600 1800 2000

F(10-10erg cm-2 s-1)

AFGL 230 AFGL 2591

5 10 15 20

Wavelength (m)

500 1000 1500

F(10-10erg cm-2 s-1) V CrB

SiC

• 4000 stars detected to have

amorphous silicates by IRAS LRS

• 700 stars detected in SiC

Unidentified infrared emission bands

2 4 6 8 10 12 14 16 18 20

Wavelength (m)

500 1000 1500

F(10-10erg cm-2 s-1 ) NGC 7027

6.2 3.3 7.7 11.3

[NeV] [SiIV] [NeIII] [MgV] 3.3: sp2 C-H stretch 6.2: sp2 C=C stretch 7.7: sp2 C-C stretch 8.6: sp2 =C-H in-plane bend 8.6 11.3: sp2 =C-H out-of-plane bend 12.0 12.7 13.5

• 11.3 µm: Gillett et al.

1973

• 3.3 µm: Merrill et al.

1975

• 6.2, 7.7, 8.6 µm:

Russell et al. 1978 (from KAO)

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11/24/2011 2 Aromatic (sp2) hydrocarbon bands

2 4 6 8 10 12 14 16

Wavelength (m)

400 600 800 1000 1200 1400 1600 1800 2000 2200 2400

F(10-10erg cm-2 s-1) Aromatic Bands in the Red Rectangle

ISO SWS01 ISO SWS06 C-H stretch C=C stretch C-C stretch C-H in-plane bend C-H out-of-plane bend

• Aromatic

grains: (Knacke 1977, Duley & Williams 1979, 1981; Puetter et al. 1979)

2 4 6 8 10 12 14 16 18 20

Wavelength (m)

• 20

20 40 60 80 100 120 140 160 180 200

F(10-10erg cm-2 s-1)

IRAS 21282+5050

3.3 6.2 7.7 8.6 11.3 6.2: sp2 C=C stretch 7.7: sp2 C-C stretch 11.3: sp2 C-H out-of-plane bend 8.6: sp2 C-H in-plane bend 12.4: sp2 C-H out-of-plane bend 12.4

When are the aromatic compounds synthesized?

• AIB features not seen in AGB stars
• AIB features are strong in young planetary

nebulae

• Have to study the missing link between

AGB and PN phases

Proto-planetary nebulae

• Objects in transition

between AGB and PN stages

• ~30 PPN are known, most

discovered as the result of follow up of the IRAS survey (Kwok 1993, Ann.

• Rev. Astr. Ap., 31, 63)

AFGL 2688, the Egg Nebula

PPN as imaged by the HST

The Walnut Nebula The Water Lily Nebula The Spindle Nebula The Silkworm Nebula The Cotton Candy Nebula

Reflected starlight, not emission!

3.4 μm aliphatic C-H stretch

• 3.38 μm: asymmetric CH3
• 3.42 μm: asymmetric CH2
• 3.46 μm: lone C-H group
• 3.49 μm: symmetric CH3
• 3.51 μm: asymmetric CH2

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Aliphatic sidegroups

3.0 3.1 3.2 3.3 3.4 3.5 3.6 3.7 3.8 3.9 4.0

Wavelength (m)

1.0 2.0 3.0 4.0 5.0 6.0 7.0 8.0

F(10-10erg cm-2 s-1)

21282+5050

3.4 3.462 3.515 3.56 3.40: asym. CH2, CH3 3.46: lone C-H group 3.51: symmetric CH2 3.29: aromatic C-H stretch Keck NIRSPEC 3.29 3.56: aldehydes C-H stretch

10 20 30 40 50

Wavelength (m)

100 200 300 400 500

F(10-10erg cm-2 s-1)

IRAS 22272+5435

ISO SWS01

6.2 6.9 7.8 26 11.3 20.3 12.2 16.0 6.2: sp2 C=C stretch 6.9: sp3 C-H bend 7.8: sp2 C-C stretch 11.3: sp2 C-H out-of-plane bend 12.2: sp2 C-H out-of-plane bend

Number of CH groups in aromatic molecules

• Solo: 11.1-11.6 μm
• Duo: 11.6-12.5 μm
• Trio:12.4-13.3 μm
• Quarto: 13-13.6 μm

Hugdins and Allamandola 1999

6 7 8 9 10 11 12 13 14

Wavelength (m)

20 40 60 80 100 120

 F ( 1 0-10 e r g c m-2 s-1 )

6.9 broad 8 22574+6609 07134+1005 7.6 6.2 11.3

ISO SWS01

12.1 13.3 12.4

Broad emission plateaus

2 4 6 8 10 12 14 16 wavelength (m) 1 2 3 4 ratioed spectrum IRAS Z02229+6208 2 4 6 8 10 12 14 16 wavelength (m) 2 4 6 8 10 ratioed spectrum IRAS 16594-4656 2 4 6 8 10 12 14 16 wavelength (m) 1 2 3 ratioed spectrum IRAS 19500-1709 2 4 6 8 10 12 14 16 wavelength (m) 4 8 12 16 20 ratioed spectrum IRAS 23304+6147

10 20 30 40 50

Wavelength (m)

1 2 3 4 5 6

ratioed spectrum

IRAS 22272+5435

ISO SWS01

6.2 6.9 4.8 26 11.3 20.3 12.2 6.2: sp2 C=C stretch 6.9: sp3 C-H bend 7.7: sp2 C-C stretch 11.3: sp2 C-H out-of-plane bend 12.2: sp2 C-H out-of-plane bend 7.7

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Aliphatic bending modes

• 8m plateau: -CH3 (7.25 m), -C(CH3)3 (8.16 m, “e”), =(CH3)2 (8.6 m, “f”)
• 12 m plateau: C-H out-of-plane bending modes of alkene (“a”, “b”), cyclic

alkanes (9.5-11.5 m, “c”), long chains of -CH2- groups (13.9 m, “d”).

Kwok et al. 2001

2 4 6 8 10 12 14 16 18

Wavelength (m)

0.0 0.2 0.4 0.6 0.8 1.0 1.2 1.4

normalized spectrum IRAS 22272+5435

11.4 12.1 6.2 6.9 13.4 14.2 7.3 7.7

10 20 30 40 50

Wavelength (m)

20 40 60 80 100 120

F(10-10erg cm-2 s-1)

23304+6147

21 m 27 m 30 m

Acetylene: first step to organic synthesis

10 20 30 40 50

Wavelength (m)

100 200 300 400 500 600

F(10-10erg cm-2 s-1 ) 21318+6531

ISO SWS01

25.5 m 20.1 m C2H2 27.5 m

5 fundamental at 13.7m.

Polymerization of C2H2 in Post-AGB evolution

13 14 15 16 17

Wavelength (m)

500 1000 1500 2000

F(10-10erg cm-2 s-1) AFGL 618

C2H2 HCN HC3N C4H2 HC5N C6H2

ISO SWS06

Chemical evolution from AGB to PN

• Extreme carbon stars (t~104 yr):

C2H2C6H6

• PPN (t~103 yr): clusters of aromatic rings

with peripheral aliphatic bonds

• PN (t~104 yr): loss of H and a progressive

formation of clusters of rings into more structured units

Advantages of circumstellar chemistry

• Single energy source
• Simple geometry
• Well-determined physical environment

(density (r), temperature T(r), radiation background I(r))

• Chemical time scale defined by dynamical

time scale (AGB: 104 yr, PPN:103 yr, PN: 104 yr)

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What is the carrier of the UIR features?

• Aromatic features: 3.3, 6.2, 7.7, 8.6, and

11.3 µm

• Aliphatic features: 3.4 and 6.9 µm
• Features at 15.8, 16.4, 17.4, 17.8, and 18.9

µm

• Broad plateau features at 8, 12, and 17 µm.

Polycyclic aromatic hydrocarbons (PAH)

• Fused ring molecules

made up of pure C and H

The PAH hypothesis

(Allamandola et al. 1989, Puget & Léger 1989)

• the UIE features are the result of infrared

fluorescence from small (~50 C atoms) gas-phase PAH molecules being pumped by far-ultraviolet photons (Tielens 2008)

• The central argument for the PAH hypothesis is

that single-photon excitation of PAH molecules can account for the 12 µm excess emission

• bserved in cirrus clouds in the diffuse interstellar

medium by IRAS (Sellgren 1984, 2001).

Problems with the PAH model

• PAH molecules have well-defined sharp features but the UIR

features are broad

• PAHs primarily excited by UV, with little absorption in the

visible

• UIR features seen in PPN and reflection nebulae with no UV

radiation

• Shapes and peak wavelengths independent of stellar temperature
• The strong and narrow predicted gas phase features in the UV are

not seen in interstellar extinction curves

• No PAH molecules have been detected in spite of the fact that

the vibrational and rotational frequencies are well known

• In order to fit the astronomical observations, the PAH model has

to appeal to a mixture of PAH of different sizes, structures (compact, linear, branched) and ionization states, as well as broad intrinsic line profiles.

Reflection nebulae

• The UIR features have

consistent profiles and peak wavelengths in spite of the fact that the nebulae are heated by central stars of 11000, 19000 and 6800 K

• No UV background

Uchida et al. (2000)

Excitation problem

• The 3.3 and 7.7 µm radiate at too short a

wavelength for the grains to be in thermal equilibrium

• Stochastic heating by single photon
• Alternate explanation: sudden release of

chemical energy as a source of transient heating (Duley and Williams 2011).

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Laboratory Simulations of Cosmic Dust

• Quenching of plasma of 4-torr methane (Sakata et al.

1987)

• Hydrocarbon flame or arc-discharge in a neutral of

hydrogenated atmosphere (Colangeli et al. 1995)

• HAC films prepared by laser ablation of graphite in a

hydrogen atmosphere (Scott and Duley 1996)

• Infrared laser pyrolysis of gas phase molecules (C2H4,

C4H6)C-based nanoparticles (Herlin et al. 1998)

• HAC polymers: photolysis of methane at low temperatures

(Dartois et al. 2004)

• Flame combustion forming soot (Pino et al. 2008) (C2H2,

C2H4, C3H6 mixed with O2) If not PAH, then what is it?

Hydrogenated Amorphous Carbon

• Aromatic rings of various

sizes bonded peripherally to polymeric of hydrocarbon species

• A mixture of sp2 and sp3

bonded carbon

• Formed when H content

exceeds 0.1 relative to C

• Similar to soot formed from

the combustion of hydrocarbons

Duley

Pure C & H or with N?

• QCC: hydrocarbon plasma deposition
• Tholins: refractory organic materials formed

by UV photolysis of reduced gas mixtures (N2, NH3, CH4, etc.)

• HCN polymers: amorphous hydrogenated

carbon nitride, formed spontaneously from HCN

Infrared Spectrum of Coal

Guillois et al. 1996

Emission plateaus

Coal

• The physical and chemical

properties of coal are entirely controlled by the chemical evolution of the Earth’s crust

• semianthraciteanthracite

semi-graphite

• Decreasing H and O content
• Change from aliphatic (sp3)

to aromatic (sp2) bonds

• graphitization

Kerogen

• random arrays of aromatic carbon sites,

aliphatic chains (-CH2-)n), and linear chains

• f benzenic rings with functional groups

made up of H, O, N, and S attached

• a solid sedimentary, insoluble, organic

material found in the upper crust of the Earth

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Origin of coal and kerogen

• Fraction of H, S, N, and O relative to C in

kerogen are similar to those in lipids  formed as the result of decay of living

• rganisms

Petroleum fractions

Anthracite coal Modified fraccion 2 Distillate aromatic extract PPN 22272+5435

Cataldo et al. 2004

Complex organic solids with disorganized structures

Kwok & Zhang 2011

• Small units of

aromatic rings linked by alphatic chains

• Inpurities of O, N, S
• A typical

nanoparticle may contain multiple of this structures

How do they form?

• Surface temperature of red giants: 3000 degrees
• Solid grains condensed from gas in the stellar

wind under near vacuum conditions

• Theoretically impossible, especially during the

PPN phase

• Observationally we see aliphatics and aromatics

form in PPN on time scales as short as hundreds of years

• In novae, they form on a time scale of days

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Aromatic & aliphatic features in novae

The 3.3 & 3.4 (left) and 8.2 and 11.4 m features of Nova V705 Cas at 253 (solid line) & 320 (broken line) days after outburst (Evans et al. 2005)

Aliphatics in novae

Kwok & Zhang 2011

Organic grains in the diffuse ISM

• 3.4 µm C–H stretch
• bserved along the

line of sight to the GC (Wickramasinghe & Allen

1983)

• Other sources: Sandford

et al. 1991, Pendleton et

• al. 1994, Chiar et al. 2000

Aliphatics in diffuse ISM

Dartois et al. 2004, Chiar et al. 2002, Dartois 2011

15% of C in sp3 bonding

Organics in the Solar System

• Planets and their satellites, asteroids,

comets, minor bodies in the outer Solar System

• Traditional picture: made up of minerals,

metals, and ices

Interplanetary dust particles

• About 30,000 tons of

IDP fall on Earth every year, higher in the early periods

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Interplanetary Dust

• Few microns to tens of

microns in size (Brownlee 1978)

• Silicates (olivine &

pyroxene)

• 10-12% carbon content
• 3.4 µm aliphatic feature and

sometimes C=O group (Flynn

et al. 2003)

O-XANES spectrum of IDP

The soluble component

• Carboxylic acids, sulfonic and phosphonic acids,

amino acids, aromatic hydrocarbons, heterocyclic compounds, aliphatic hydrocarbons, amines and amides, alcohols, aldehydes, ketones, and sugar related compounds

• Almost all biologically relevant organic

compounds are present in carbonaceous meteorites C and N isotopic ratios suggest interstellar origin (Martins et al. 2008; Nakamura-Messenger et al. 2006)

Carbonaceous Chondrite Meteorites

• Pre-biotic organic matter
• Insoluble

macromolecular material similar to kerogen (Kerridge 1999), possibly

• f interstellar origin due

to excess of D, 13C, 15N, etc.

Functional groups identified in Murchison IOM (Cody 2008)

Spectral profiles of IOM similar to interstellar 3.4 µm features (Ehrenfreund et al. 1991)

Pre-solar grains

• Isotopic studies of

meteorites have also identified grains of presolar origin, including diamonds (Lewis et al. 1987), SiC (Bernatowicz et al. 1987), corundum (Al2O3) and spinel (MgAl2O4) (Nittler et al. 1997).

Scanning electron microscopic micrograph of a 4 m pre-solar SiC crystal from the Murchison meteorite.

Burning down a haystack to find a needle

Planetary satellites

• Cassini-Huygens
• bservations of the

Saturnian satellite Titan

• Total amount of

hydrocarbons on Titan is larger than the oil and gas reserves on Earth

Comparison between 3.4 µm features in Titan haze, comets, and PPNs

Kim et al. 2011

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Primordial solids

• Most of the original solar nebula was

incorporated in the Sun, with the remaining planetesimals aggregated into planets

• Small fractions of the pristine materials

reside in comets and asteroids which were not subjected to extensive processing

• Effects of exogenous delivery (Anders

1989, Chyba & Sagan 1992)

Summary

• Organic compounds are everywhere in the

Universe (from solar system to ISM to galaxies)

• Hydrocarbons with linear, aromatic and aliphatic

structures are detected in the circumstellar envelopes of evolved stars

• These carbonaceous materials undergo a change

from aliphatic to aromatic structures during the transition from PPN to PN

• Chemical evolution leading to complex organic

compounds can take place over only a few thousand years in the circumstellar environment

Summary (cont.)

• The detection of pre-solar grains suggests that

grains from AGB stars can survive the journal through the ISM and reach the Solar System

• Macromolecular organics in meteorites, IDP,

comets, and planetary satellites show similarities with organics produced by planetary nebulae

• To what extent was the Early Earth chemically

enriched by the early bombardment?

A star-Earth connection

References

Kwok, S. 2004 The Synthesis of Organic and Inorganic Compounds in Evolved Stars, Nature, 430, 985 Kwok, S. & Zhang, Y. 2011, Mixed aromatic/aliphatic organic nanoparticles as carriers of the unidentified infrared emission features, Nature, 479, 80