1. Influence of H2 formation on PDR model results M. Röllig V. Ossenkopf, C. Glück Universität zu Köln, Germany CO Ladder Workshop - Leiden 2012

2. Outline H 2 formation on grain surfaces – chemisorption vs. physisorption – H 2 formation efficiencies on different dust sorts – chemical H 2 heating & cooling – effects on clump structure CO Ladder Workshop - Leiden 2012

3. Introduction Numerical PDR models of proved to be a valuable tools in analyzing and understanding the local conditions in massive star forming regions. Ossenkopf et al, 2010, A&A 518, L79v Hollenbach & Tielens, 1999, R.o.m.P., 71 CO Ladder Workshop - Leiden 2012

4. Introduction Yet, here be dragons... complex physics / chemistry complex/unknown local conditions Röllig et al. 2007, A&A, 467 θ 1 Ori C (O6) CO Ladder Workshop - Leiden 2012

5. Introduction and unfortunately, deficient input data missing experimental data inter/extrapolation CO Ladder Workshop - Leiden 2012

6. H 2 formation on grain surfaces CO Ladder Workshop - Leiden 2012

7. H 2 formation on grain surfaces H atoms hitting grain surfaces can stick weakly (physisorption) or strongly (chemisorption) bound. T d >100 K desorption overcomes binding and H 2 formation efficiency →0 Chemisorbed H atoms can effectively form H 2 up to T d >500K we implemented the formalism presented by Cazaux & Tielens (2002,2004) in the KOSMA-  chemistry. CO Ladder Workshop - Leiden 2012

8. H 2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

9. H 2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

10. H 2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

11. H 2 formation efficiency Cazaux & Tielens 2004, ApJ 604 CO Ladder Workshop - Leiden 2012

12. H 2 formation rate total formation rate depends on total dust surface CO Ladder Workshop - Leiden 2012

13. H 2 formation rate CO Ladder Workshop - Leiden 2012 Weingartner and Draine, 2001, ApJ 548

14. H 2 formation rate CO Ladder Workshop - Leiden 2012

15. H 2 heating/cooling H 2 binding energy 4.5 eV → H 2 formation heating kinetic H 2 dissociation cooling ( Lepp & Shull, 1983, ApJ 270, 578 ) H 2 + H → H + H + H - 4.5eV H 2 + H 2 → H 2 + H + H - 4.5eV Alternatively: sticking coeff. CO Ladder Workshop - Leiden 2012

16. H 2 heating/cooling CO Ladder Workshop - Leiden 2012 Le Bourlot et al. 2012

17. H 2 heating/cooling CO Ladder Workshop - Leiden 2012 Le Bourlot et al. 2012

18. H 2 heating/cooling CO Ladder Workshop - Leiden 2012 Le Bourlot et al. 2012 A: R=const, B: only LH, C=LH+ER

19. H 2 heating/cooling CO Ladder Workshop - Leiden 2012 Le Bourlot et al. 2012 A: R=const, B: only LH, C=LH+ER

20. Dust influence CO Ladder Workshop - Leiden 2012

21. Dust influence CO Ladder Workshop - Leiden 2012 radiative transfer effect H 2 chemistry effect

22. Dust influence H 2 binding energy 4.5 eV → H 2 formation heating kinetic H 2 dissociation cooling ( Lepp & Shull, 1983, ApJ 270, 578 ) H 2 + H → H + H + H - 4.5eV H 2 + H 2 → H 2 + H + H - 4.5eV large effect on H-H 2 transition region chemistry CO Ladder Workshop - Leiden 2012

23. Dust influence H 2 binding energy 4.5 eV → H 2 formation heating kinetic H 2 dissociation cooling ( Lepp & Shull, 1983, ApJ 270, 578 ) H 2 + H → H + H + H H 2 + H 2 → H 2 + H + H large effect on H-H 2 transition region chemistry chemistry  physics CO Ladder Workshop - Leiden 2012

24. Summary Great need for reliable (astrochemistry) data Lab results need to be robust against different modeling applications Growing understanding of dust properties and H 2 formation process dramatically influences model results chemistry and physics strongly connected to each other CO Ladder Workshop - Leiden 2012