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Formation and Evolution of Molecules Behind Shocks GEORGE HASSEL Dept. of Physics, The Ohio State University Eric Herbst (Ohio.

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Presentation on theme: "Formation and Evolution of Molecules Behind Shocks GEORGE HASSEL Dept. of Physics, The Ohio State University Eric Herbst (Ohio."— Presentation transcript:

1 Formation and Evolution of Molecules Behind Shocks GEORGE HASSEL Dept. of Physics, The Ohio State University Eric Herbst (Ohio State), Ted Bergin (U. Michigan) SATURDAY, NOVEMBER 8, 2008 MWAM08

2 OVERVIEW Can shocks form dense clouds from diffuse ISM? (Bergin et al. 2004) Replicate molecular observations? –Ice composition with A V (Whittet et al. 2007, Nummelin et al. 2001) –Complex gas molecules: L134N, TMC-1 (Ohishi et al 1992, Wakelam, Herbst & Selsis 2007)

3 Modifications: Read shock hydro results as input Compute dust temperature New / modified rates: –Photodesorption –Eley-Rideal –CO + O surface barrier OSU GAS-GRAIN NETWORK Grain Model: r = 0.1 m Spherical, silicate grains Rate equations – no stochastic methods

4 Shock Chemistry Model Hydrodynamical 1 point model (Bergin et al. 2004) Diffuse ISM -> Shock -> Dense cloud? Formation of H 2 (g) & CO(g) - ices & complex species? Photos from NASA-APOD Archive

5 Physical Conditions n H, T g – dense cloud ~ yr A V, T d – more gradual change

6 Photodesorption Rates CO: Direct photodesorption Temperature dependent CO 2 : Photodissociation / desorption Temperature, coverage dependent N 2 : Direct photodesorption only with CO **indicates non-thermal** H 2 O: Photodissociation / desorption Oberg et al. 2007, in prep.

7 Ice – No Photodesorption Ices: Whittet et al. 2007, CO(g): Ohishi et al 1992 (TMC-1, L134N)

8 Ice – Photodesorption

9 Ice Composition Formation at A V ~ 3-4 OH(s) + H(s) -> H 2 O(s) CO(g) -> CO(s)

10 Ice Composition CO(s) + OH(s) -> CO 2 (s) CO 2 (s) + h -> CO(s) + O(s) CO(s) + O(s) -> CO 2 (s) E A = 290 K (Roser et al. 2001) = 130 K (Ruffle & Herbst 2001)

11 CO 2 Ice T d0 =20 K E A = 130 K E A =290 K T d0 =15 K E A = 130 K E A =290 K

12 Complex Gas Molecules H2SH2SNH 3 HC 3 N 14 species 6 species species

13 Conclusions Ice composition: H 2 O : CO : CO 2 ~ observed abundances A V Threshold CH 4 minimized Governed by photodesorption Gas phase molecules – 3 distinct evolution stages

14 Acknowledgements Rob Garrod Herma Cuppen & Karin Oberg MWAM 08 Organizing Committee

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