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); CO N,T similar to cloud UV radiation + cosmic rays LTE CO, C 2 H 2, HCN, H 2 Dust and PAHs 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!!!