ERIC HERBST DEPARTMENTS OF PHYSICS AND ASTRONOMY THE OHIO STATE UNIVERSITY The Production of Complex Molecules in Interstellar and Circumstellar Sources

Dust particles contain 1% of interstellar matter.

Cosmic rays produce ions some radical-stable reactions

Radical-Stable Neutral Reactions Radicals: C, CN, CCH 1) Inverse T dependence 2) Large rate coefficients by K: k  10(-10) cm 3 s -1

FORMATION OF GASEOUS WATER H 2 + COSMIC RAYS  H e Elemental abundances: C,O,N = 10(-4); C<O H H 2  H H H O  OH + + H 2 OH n + + H 2  OH n H H 3 O + + e  H 2 O + H; OH + 2H, etc

C 3 + H 2

NEUTRAL-NEUTRAL RX (CONT) CN + C 2 H 2  HCCCN + H CCH + HCN  HCCCN + H YES NO CCH + C 2 H 2  C 4 H 2 + H YES O + CCH  CO + CH MAYBE (E a = 250K?) k  (-11) cm 3 s -1

O Reactions at Low Temperature (cm 3 s -1 )

UNSATURATED SPECIES HYDROGENATION WITH H2 DIFFICULT BARE CLUSTERS PROMINENT EXCEPTION: HOT CORES (NEAR NEW HIGH-MASS STARS) WHERE GRAIN MANTLES EVAPORATE!!

Quiescent cores: (1)Reproduces 80% of abundances including ions, radicals, isomers (10 5 yr); (2) For longer times, use gas-grain model.

TOWARDS FULLERENES No. Carbon Atoms n 2448 Linear Chains Monocyclic Rings Tricyclic Rings Fullerenes Spontaneous Isomerization condensation He + conversion GROWTH BY C+/C ADDITION Bettens, Herbst 1995,1996

IMPORTANT SYNTHETIC RX C + + C n H m  C n+1 H m + + h C n+1 H m + + e   C n+1 H m + h C + C n H m  C n+1 H m + h

RESULTS FOR FULLERENES RESULTS VERY DEPENDENT ON REACTIVITY OF LINEAR CLUSTERS AND UNSATURATED HYDROCARBONS WITH O ATOMS, WHICH ARE VERY ABUNDANT IN OXYGEN-RICH REGIONS. WHAT ABOUT CARBON-RICH REGIONS? Extended to synthesis of dust particles in supernova remnants by Liu, Clayton, Dalgarno

IRC10216: An AGB (Old) Star Molecules and dust here C>O N,T similar to cloud UV radiation + cosmic rays LTE CO, C 2 H 2, HCN, H 2 Dust and PAH’s

PAH/DUST PRODUCTION Occurs close to stellar photosphere (HOT; K) a) Formation of benzyl radical A 1 - from acetylene b) Reaction with acetylene to add CCH A C 2 H 2  A 1 CCH + H c) Radical formation A 1 CCH + + H  A 1- CCH + H 2 d) Ring addition A 1 CCH * + C 2 H 2  A 2-

Actual Distributions

GROWTH OF MOLECULES Occurs via neutral and ionic (+ and -) reactions. Modified network necessary to account for acetylenic chemistry. Photochemistry important in the production of radicals such as CN and CCH (Millar, Herbst, Bettens 2000) C 2 H 2 + h  CCH + H

GROWTH OF MOLECULES. II CCH + C 2n H 2  C 2n+2 H 2 + H CN + C 2n H 2  HC 2n+1 N + H C 2n H reactions with hydrocarbons, HCN(?), HNC(?) as well as cyanoacetylenes.

GROWTH OF MOLECULES. III C 2 H C 2n H m  C 2n+2 H m H e + C n  C n - + h C n - + C m  C n+m - + h Model network through 23 C atoms: unsaturated species prevail!! BUT…..

CYANOPOLYYNES in IRC Radius 

DETECTABLE LARGE SPECIES SPECIES Cal. Col. Dens. (cm -2 ) Measured HC9N5.8(13)3(13) HC15N9.1(11) C8H1.1(14)5(12) C10H1.8(13) C8H - 2.7(13) C6H63.0(13) CRL618 (100X) % Agreement

CRL618: A Protoplanetary Nebula empty Dense Thin Slab (500 yr old) 250 K Detection of benzene Photons, X-rays from central star! 500 x normal ionization rate Woods et al. 2002

SYNTHESIS OF BENZENE C 2 H C 2 H 2  C 4 H H C 4 H C 2 H 2  c-C 6 H h c-C 6 H H 2  c-C 6 H h c-C 6 H e  c-C 6 H 6 + H

SUMMARY A. COMPLEX CARBONACEOUS SPECIES ARE PRODUCED BOTH IN OXYGEN-RICH AND CARBON-RICH OBJECTS B. THE BEST SOURCE FOR DETECTING SUCH MOLECULES MAY BE THE COMPLEX PROTOPLANETARY NEBULA CRL 618. ACCORDING TO MODEL, COLUMN DENSITIES ORDERS OF MAGNITUDE GREATER THAN IN IRC+10216!!!