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LABORATORY STUDIES OF LOW TEMPERATURE GAS PHASE CHEMISTRY AND AEROSOL FORMATION IN TITAN’S ATMOSPHERE

Kevin Wilson Chemical Sciences Division, Lawrence Berkeley National Laboratory

Jordy Bouwman, Fabien Goulay, and Stephen LeoneChemical Sciences Division, Lawrence Berkeley National Laboratory

Department of Chemistry University of California Berkeley

Satchin SoorkiaInstitut des Sciences Moléculaires d'Orsay

Université Paris-Sud 11, Orsay, France

Jesse Kroll and Kelly DaumitDepartment of Civil and Environmental Engineering

Massachusetts Institute of Technology

Hiroshi ImanakaDepartment of Chemistry and Biochemistry

University of Arizona Funding

Surface growth

Atmospheric Chemistry of Titan

“Tholins”Complex Formationand Heterogeneous Chemistryty

Particle nucleation

.. . ...

and Heterogeneous Chemistry

sing

che

mic

al c

ompl

exit

Molecular zone

CH

H2O

CN

C2H

C

Rate CoefficientsProduct Branching Ratios

C2H• + C2H2, C2H4, C3H6

Incr

eas

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Titan’s atmosphere in the lab: Pulsed Laval Nozzle

Low temperature chemistry (75 – 295K)

Pressure (0.1 – 1 Torr)

C2H2 + 193 nm C2H + H

Rowe et al., J. Chem. Phys. (1984) 80, 4915 (CRESU)

Atkinson & Smith, Rev. Sci. Instrum. (1995), 66, 4434 (PULSED LAVAL)

Gas pulse

Pulsed Laval Nozzle Kinetics

Uniform Densityand Temperature

Laser kinetic window

p

Kinetic measurements made over region of uniform temperature and density of gas pulse

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Pulsed Laval Nozzle Kinetics: Radical – Neutral Reactions

D t ti f R di l iDetection of Radicals via:

Chemiluminescence (C2H)

Laser Induced Fluorescence (OH)

Rate Coefficient (k)

C2H + C2H2 products?k

C2H

Synchrotron-Based Product Detection via Photoionization Mass Spectrometry

The Chemical Dynamics Beamline7-30 eV (1013 to 1015 photons/s)Resolution = 0.010 to 0.1 eV

7-30 eV Vacuum Ultraviolet (VUV)photons

Kinetic reaction tube and sampling aperture (Osborn and Coworkers, Sandia)

Flame sampling mass Spectrometer(Cornell, Sandia, etc.)

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Isomer Identification via Photoionization Efficiency Spectrum (PIE)

m/z=42 (C3H6)

Person and Nicole (J. Chem. Phys. 53, 1767 (1970))

Pulsed Laval Vacuum Ultraviolet Mass Spectrometer

Rate Coefficients

Product Branching Ratios

Airfoil Laval nozzlePhotolysis

laser

Synchrotron

Vf = 675 m/sVf = 675 m/s

Hassan Sabbah, Ludovic Biennier, CRESU

Quadrupole

Collimated Laval beam(Pi)

Laval nozzle Block(Ps)

Stephen J. Klippenstein, Ian R. Sims, and Bertrand R. Rowe, J. Phys. Chem. Lett., 2010, 1 (19), pp 2962–2967

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Kinetic measurements via Time-Resolved Mass Spectrometry

Chemical evolution (k)

Sampling

x

Rulex 2kT

m 0 1

t 0.1

Rule of thumb for kinetic validity:

• x : distance• : rate coefficient• δt: full width in arrival time

Spread in arrival time (∂t)

… where to ionize?

Taatjes: Int. J. Chem. Kinet. 39 565-570, 2007; Moore and Car, Int. J. Chem. Kinet, 1977

Synchrotron

m

2kT

m u

2 0.1 • T : temperature• k : Boltzmann constant• u : initial velocity• m: mass

Molecular velocity distribution & Kinetics measurement by Time-Resolved Mass spectrometry

Sampling

x

10

Taatjes: Int. J. Chem. Kinet. 39 565-570, 2007

Synchrotron

κ = f(x)

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Quadrupole(QMS)

Pulsed Laval Nozzle Vacuum Ultraviolet Mass Spectrometer

Molecular beam

Detection chamber10-6 Torr

Airfoil

(QMS)

Source chamber0.15 – 1 Torr

External photon sourceLaser/synchrotron

Excimer Laser

Pulsed Laval Nozzle Vacuum Ultraviolet Mass Spectrometer

Roots Blower

Laval Nozzle

Airfoil

Excimer Laser248 and 193 nm

Roots Blower1200 CFM

Mass Spectrometer

2 X 2000 L/sTurbomolecular Pumps

A user machine Funded by NASA Planetary Equipment Request (2009)

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N2+ signal from mass

Comparison with Other Sampling Geometries

30° angle skimmer Ionization at 12 cm

N2 signal from mass spectrometer

Lee and coworkers (Rev. Sci. Instrum., 71, 4, 2000). 

Photodissociation of 1,3 Butadiene

Photodissociation of 1, 3 Butadiene

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Beam Velocity

kT T 72Kv flow

kTflow

mM

gamma = 1.4k = Boltzmann constantM = 4 (Mach number for M4 nozzle)m = mass

Tflow 72K

C2H + Acetylene

++ C4H2 + Hm/z = 50

m/z = 50

Increasing[C2H2]

[C4H2] = [C2H]0 (1-exp(-kobst))

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C2H + Acetylene

k = 1.34 x 10-10 cm3 molec.-1 s-1

Photoionization vs. Photon Energy(PIE): C2H + Acetylene

di l

m/z = 50

diacetylene

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C2H + Ethylene (C2H4)

++ C4H4 + HC2H4

m/z = 52

Increasing[C2H4]

C2H + Ethylene (C2H4)

k = 1.14 x 10-10 cm3 molec.-1 s-1

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C2H + Ethylene (C2H4)

Vinylacetylene

m/z = 52

Consistent with Crossed

Vinylacetylene

Ion

Cou

nts

++ C4H4 + HC2H4

Molecular Beam Study ofZhang et al. JPC, 2009

C2H + Propene (C3H6)

++C5H6 + H m/z = 66

C4H4 + CH3 m/z = 52C4H4 CH3 m/z 52

m/z = 52

Increasing[C3H6]

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C2H + Propene (C3H6)

k = 2.42 x 10-10 cm3 molec.-1 s-1

C2H + Propene (C3H6)

++ C4H4 + CH3 m/z = 52

m/z = 52

Vinylacetylene

n C

ount

sIo

n

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C2H + Propene (C3H6)

++C5H6 + H m/z = 66

13 stable isomers

m/z = 66

Ionization energies from NIST WebBook

Low temperature kinetics & product detection

C H +C H +

2-vinylpyridine Styrene

C2H + C2H +

Pyridine

CH•

PyrroleRing Expansion

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Laboratory Simulated Haze

From Sagan and Khare, Nature, 277, 1979

Molecularly complex “Reduced Variable Descriptions”

Carbon Oxidation State

methaneoxidation

C5 carbonchain

Ox. State ≈ 2 (O/C) ‐ (H/C) ‐ x (N/C) 

Exceptions:- peroxides (O: -1)- heteroatoms (N: -3…+5; S: -2…+6; etc.)

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Carbon Oxidation State Representation

CO2

Kroll et al., Nature Chemistry, 2011

oleicacid

acetaldehydephenanthrene

sucrose levoglucosan

sesquiterpene monoterpene isoprene

C5 tetrol

CH2O

glyoxalglyoxaldimer

oxalicacid

pinonicpinic

C8triacid

butaneoctane

toluene

CO

MVK

methylglyoxal

fulvicacid

dodecaneCH3OH

elementalcarbon, cellulose

ethane

butane

CH4

CO2

Oxidation State Evolution: Present Day Earth

Aerosol Envelope

CO

e oso e ope

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Oxidation Pathways: Present Day Earth

oligomerization

Carbon Oxidation State RepresentationJesse Kroll and Kelly Daumit (MIT)Hiroshi Imanaka (University of Arizona and SETI)

Neglect N=N and N-O bondsAssumes Nitrogen Oxidation state = -3 (CN, NH . . .)

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Molecular Weight Growth: HCNx, Polyyne, PAH’s

HCNx

CH4

+ C2H -H

“HACA”

4

Changes in Carbon Oxidation State with Chemistry

Nitrogen Fixation

+ CN

“Polymerization”CH4

Photolysis?

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Imanaka and Smith, JPCA 2009Imanaka and Smith, GRL 2007Imanaka and Smith, PNAS 2010

Laboratory Simulated Haze: EUV Photolysis of CH4/N2

High Resolution Mass Spectrometrym/Δm = 3 x 107

Collect solid material for analysis

Solid Material= 82.5 nm = “Nitrogen Rich”

LDI-FTICR-MS

5000 peaks between m/z = 200-700

Unambiguous assignment of CvHxOyNz

g= 60 nm = “Carbon Rich”

High Res. Mass Spectral Data from Imanaka and Smith PNAS 2010

Aerosol Formation: Irradiate N2/CH4 at82.5 nm (15 eV)

HCNx = +2

“Nitrogen Rich” Aerosol

Assume oxidation state of N is -3Neglects N=N and N-O bonds

C7 - C14

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Aerosol Formation at 60 nm (20.6 eV)High Resolution Mass Spectral Data from Imanaka and Smith PNAS 2010

C2H2N = +0.5

HCCN + aerosol growth

C10-C19

High Res. Mass Spectral Data from Imanaka and Smith PNAS 2010

Heterogeneous Growth at 60 nm (20.6 eV)

+ HCCN

Polyacetylene

HCCN + aerosol growth

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Conclusion

Low Temperature Isomer Resolved Product DetectionRate Coefficient

Airfoil Laval nozzlePhotolysis

laser

Synchrotron

Vf = 675 m/sVf = 675 m/s

60 nm

82.5 nm

Chemical Evolution of

Quadrupole

Collimated Laval beam(Pi)

Laval nozzle Block(Ps)

60 nmChemical Evolution of Carbon Oxidation State

CH4

?

Laval Nozzle (LBNL, Berkeley Lab)

Acknowledgements

Funding

Jordy BouwmanFabien GoulaySatchin Soorkia (Université Paris-Sud 11)Stephen Leone

Carbon Oxidation State

Jesse Kroll and Kelly Daumit (MIT)Hiroshi Imanaka (U. of Arizona, SETI)