3. The Chemistry of Interstellar Space What did you just see? SCIENCE = WHAT IS GOING ON? AND WHY? Science is not reality, Science tries to give a DESCRIPTION of the reality

4. The Chemistry of Interstellar Space D A Adriaens / F Goumans (ex-)UCL Chemistry Department

5. The Orion Nebula Astronomy History Star Cycle Chemistry Nuclear Reactions Spectra Molecules in the universe

6. Stonehenge 2900 BC  2000 BC Astronomical calendar or Religious Temple Midsummer and Midwinter Go back to main

7. History Greek –Aristarchus (310-230BC): sun in centre of the universe –Aristotle (384-322BC): earth in centre of the universe –Ptolemy (90-168AD): earth in centre of the universe China –1054: Supernova

8. History 16-17th century: Age of Enlightenment –Copernicus (1473-1543) (heliocentrism, circular orbits) –Galileo Galilei (1564-1642) (4 moons of Jupiter) –Johannes Kepler (1571-1630) (3 laws of Kepler, ellipses) –Newton (1643-1727) (3 laws of motion) –… Revolution in Sciences

9. History Now ? –Albert Einstein (1879-1955) –Stephen Hawking (1942-…) > relativity and advanced cosmology “A brief history of time”

10. Star Cycle Only via STATIC observations, not dynamic Go back to main

11. Star Cycle

12. Only via STATIC observations, not dynamic

13. Nuclear reactions in a star Small stars: H  He Medium stars: H  He  C Massive stars: H  He  C  O  Ne, Na, Mg, S, Si, Ca, Fe, Ni, Cr, Cu, … Basis for life “We are all made of stars” Go back to main

14. Nuclear reactions: proton-proton

15. Nuclear reactions in a star 1 H + 1 H  2 H + e + + e 1 H + e - + 1 H  2 H + e 2 H + 1 H  3 He +  3 He + 1 H  4 He + e + + e 3 He + 3 He  4 He + 1 H + 1 H 3 He + 4 He  [ 7 Be] +  [ 7 Be] + e -  7 Li + e 7 Li + 1 H  4 He + 4 He [ 7 Be] + 1 H  8 B +  8 B  8 Be + e + + e 8 Be  4 He + 4 He 4 He + 4 He  [ 8 Be] 4 He + [ 8 Be]  12 C +  4 He + 12 C  16 O +  12 C + 1 H  [ 13 N] +  [ 13 N]  13 C + e + + e 13 C + 1 H  14 N +  14 N + 1 H  [ 15 O] +  [ 15 O]  15 N + e + + e 15 N + 1 H  12 C + 4 He 15 N + 1 H  16 O +  16 O + 1 H  [ 17 F] +  [ 17 F]  17 O + e + + e 17 O + 1 H  14 N + 4 He

16. Spectra: The sun Why is our sun yellow? Go back to main

17. Spectra

18. Spectra: solar spectrum

19. Absorption and emission

20. Some atomic spectra H He Li Be B C N O F Ne Na Mg Al Si P S Cl Ar K Hg

21. An owl’s view on the Universe

22. Infrared spectra Molecular spectra: more complicated

23. The Orion Constellation Seeing in the Infrared

24. An owl’s view on the Universe

25. Molecules in the Interstellar Matter clouds of dust these regions are nurseries for stars rich in complex molecules Go back to main

26. Molecules in the ISM > 150 species from H 2 to HC 11 N

27. Role of molecules Stars form in gas clouds collapsing under their own weight Must dissipate heat formed in process Heat radiated away by molecules

28. Spectroscopy of stars Region of spectrum characteristic to motion Rotation Vibration Electronic excitation Radio Infrared Microwave Visible/UV Wavelength Go back to main

29. Formation of molecules Conditions very harsh in the ISM –Extremely low pressure (10 -15 mbar): few collisions –Extremely low temperature (10-20K): barrierless Very low chance of reactive encounters

30. Formation of molecules For several molecules ‘too high’ abundances for gas-phase reactions only H 2 Formation problem H + H  H 2 *  H 2 + hv H + H  H 2 * H 2 * + M  H 2 + M Interstellar Ices Gas phase alone cannot account for observed abundances  DUST GRAINS

31. Dust grains Gas clouds contain dust particles Molecules freeze out as “ices” (~10K) Ices grow by reactions at grain (H, N, O, CO yielding H 2 O, NH 3, CO 2, CH 3 OH)

32. Dust grains ~1% of the mass of the ISM up to 10mm in size carbonaceous and silicate material bare or covered by ices –H 2 O, CO, CO 2, CH 3 OH, NH 3 amorphous fluffy, open structure (porous)

33. Formation of molecules Heterogenous reaction at the dust particle’s surface –H 2 formed by such a reaction 2 mechanisms: –2 H meet on surface (Langmuir-Hinshelwood) –1 gaseous H meets an H on surface (Eley-Rideal) Other molecules formed on surfaces: –H 2 O, CO, CO 2, CH 3 OH and NH 3 (yielding ices)

34. Ice formation Mechanisms of formation unknown We ‘assume’ some reaction model CH 3 OH formation CO a + H a  HCO a + Ha Ha  CH 2 O a + Ha Ha  CH 3 O a + H a  CH 3 OH a H 2 O formation Oa Oa + H 2,a  OH a + H(g) OH a + H 2,a  H2Oa H2Oa + H(g)

35. Experiments Experimentalists mimic the interstellar medium –low T and p –use model surfaces –observe ad/desorption and reactions:

36. Simulating the ISM

37. What do experimentalists do? Surface infrared spectroscopy –which molecules are adsorbed? Temperature-programmed desorption –which molecules adsorbs most strongly?

38. Theory Theoretical chemists calculate reaction mechanisms –Explain/clarify experiments –Experimentally inaccessible data Theoretical physicists model star formation Data

39. Summary Chemistry important in the evolution of the universe Molecules play a crucial role in star formation –loss of heat during collapse (Some) molecules formed on dust grain surfaces Chemists are investigating reactions in the lab Theoreticians are computing reactions  Understanding star formation and the universe

40. http://www.ucl.ac.uk/chemsea Acknowledgements Contact me via: drdadriaens@googlemail.com Thanks to: Dr Fedor Goumans Dr Wendy Brown Rosie Coates Imperial College Go back to main