Organic Reactive Intermediates and the Chemistry of Interstellar Space

Nathan P. Bowling Nicola J. Burrmann Jeffrey T. DePinto Brian J. Esselman Robert J. Halter Jonathan A. Hodges Jessica L. Menke Eric V. Patterson Randal A. Seburg Christopher J. Shaffer Phillip S. Thomas Katherine Traynor R. Claude Woods Robert J. McMahon

University of Wisconsin National Science Foundation

Chemistry Division Astronomy Division

Collaborators

Robb J. Wilson Sean A. Peebles Robert L. Kuczkowski

University of Michigan Francis J. Lovas

NIST Jens-Uwe Grabow

Universität Hannover Anthony J. Remijan

National Radio Astronomy Observatory

Benjamin J. McCall University of Illinois

Susanna L. Widicus Weaver Emory University

Christopher S. Simmons Kurt W. Sattelmeyer John F. Stanton

University of Texas Jürgen Gauss

Universität Mainz James Mack Lawrence T. Scott

Boston College John B. Dudek Carl A. Gottlieb Michael C. McCarthy Patrick Thaddeus

Harvard-Smithsonian Center for Astrophysics

Carbon-Rich Molecules

Combustion chemical intermediates

in flames

Soot Formation fullerenes

carbon nanotubes

Space understanding our physical universe

origin of life

Interstellar Molecules H2C=NH CH3OH CH3NH2 HCO2CH3 CH3CH2OH H2C-CN CH3SH CH3C≡CH CH3C2CN CH3OCH3

H2N-CN HCONH2 CH3CHO HOCH2CHO CH3C4H H2C=C=O HC≡CCHO CH2=CHCN CH2=CHCHO CH3CH2CN HCO2H CH3CN HC5N H2NCH2CN HC7N SiC4 CH3NC HC6 H2C6 HC8

H2C3 C5N HC6− HC7 HC8

−

HC≡CCN H2C4

HC≡CNC HC5 CH3CH2CHO HC3N (CH3)2CO HC4

HC4−

C60

C70

HC9N HC11N

Organic Chemistry Astrochemistry

Identify chemically significant targets Rosetta Stone vs. Stamp Collecting

Aromatic Compounds and PAHs

Rotational spectroscopy of stable & reactive species

Electronic absorption spectroscopy of reactive intermediates

Important Targets for Astronomy

Chemical Mechanism linking

acyclic species ubiquitous in the

interstellar medium and

aromatic species widely hypothesized

but undetected

Benzene in PPNe: Ion Route

Woods, Millar, Herbst, Zijlstra A&A 2003, 402, 189

PAH Formation

Frenklach and Feigelson Astrophys. J. 1989, 341, 372

Cherchneff, Barker, Tielens Astrophys. J. 1992, 401, 269

Important Targets for Astronomy

Chemical Mechanism linking

acyclic species ubiquitous in the

interstellar medium and

aromatic species widely hypothesized

but undetected

Synthesis and Isolation of Enediyne

Structural Analogs

Kuczkowski, Stanton, McMahon, coworkers J. Am. Chem. Soc. 2001, 123, 12353

µ = 0.18 D µ = 3.53 D µ = 5.25 D

synthesis of isotopomers molecular structure determination

rotational constants, dipole moment

Strategies to Probe for Aromatics

Direct Detection of Polar Rings

Mechanistic and Structural Inference

FT Microwave Spectroscopy

Thaddeus, Gottlieb, McCarthy Harvard-Smithsonian

Center for Astrophysics

Benzene Discharge

•  optimize signal of o-benzyne •  search for fundamental 11,1 → 00,0 transition

predicted at 9.2 or 9.4 GHz; scan 9.0 – 9.6 GHz •  observe several candidates

rule out most on basis of magnetic behavior •  complex (blended) spectrum

hyperfine, spin-rotation splittings comparable

Phenyl: FT-Microwave Data

a (G) A (MHz) ortho 17.4 48.8 meta 5.9 16.5 para 1.9 5.3 εcc 4.78

Benzene Discharge

observation of protoplanetary nebula

CRL 618

Radio Astronomy Search for Phenyl, o-Benzyne

Anthony J. Remijan National Radio Astronomy Observatory

Susanna L. Widicus Weaver Benjamin J. McCall

University of Illinois Robert J. McMahon

University of Wisconsin

Robert C. Byrd Telescope National Radio Astronomy

Observatory Green Bank, WV

o-benzyne column density

< 1015 cm-2

Astrophys. J. 2007, 671, L153-L156

Organic Chemistry Astrochemistry

Identify chemically significant targets Rosetta Stone vs. Stamp Collecting

Aromatic Compounds and PAHs

Rotational spectroscopy of stable & reactive species

Electronic absorption spectroscopy of reactive intermediates

Astrophys. J. 2011, 726, 1-9

known interstellar molecule absorptions across the visible transparent 260-400 nm

not responsible for prominent DIB features

serious candidate for other DIB features

matrix spectrum (solid state) not sufficient for critical comparison with DIB spectra

high resolution gas-phase spectrum is required

Electronic Spectrum of Propadienylidene (H2C=C=C:) and Its Relevance to the Diffuse Interstellar Bands

Hodges, McMahon, Sattelmeyer, Stanton Astrophys. J. 2000, 544, 838

Diffuse Interstellar Bands vs. H2C=C=C: in Neon

known interstellar molecule absorptions across the visible transparent 260-400 nm

not responsible for prominent DIB features

serious candidate for other DIB features

matrix spectrum (solid state) not sufficient for critical comparison with DIB spectra

high resolution gas-phase spectrum is required

Outlook Astrochemistry

need a much deeper understanding of the organic chemistry

of astronomical environments

ALMA will provide opportunities and capabilities

to address these questions

Will require good communication and collaboration between

observational and laboratory spectroscopy

Benzene in PPNe: Radical Route

Frenklach and Feigelson Astrophys. J. 1989, 341, 372

Phenyl: Spectroscopic Constants Constant Expt (MHz) Theory A 6279.8(3) 6282 B 5599.9(2) 5599 C 2959.4009(6) 2959 103 ΔJ 1.419(4) 1.89 103 ΔJK −2.39(1) −3.22 103 ΔK 1.09(6) 1.46 εcc 4.78(2) ---

Inertial Defect (amu Å2) Δ 0.046(5) 0.043 Watson’s A-reduced Hamiltonian

Essential Data for Accurate Prediction of Astronomically

Relevant Frequencies (Rest Frequencies)

McMahon, McCarthy, Gottlieb, Dudek, Stanton, Thaddeus Astrophys. J. 2003, 590, L61-L64