1. Forschergruppe Laboratory Astrophysics

2. + + + + + + + + Interstellar Molecules

3. Schlemmer, Cook, Saykally, Science 265, 1686 (1994) Cook, Schlemmer, Saykally, Nature 380, 227 (1996) Cook, Schlemmer, et al. J.Phys.Chem. A102, 1465 (1998)

4. Forschergruppe Laboratory Astrophysics

5. Cosmic Abundance of some elements Element Abundance hydrogen (H) 1.000.000 helium 80.147 oxygen 739 carbon 445 neon 138 nitrogen 91 magnesium 40 Silcon 37 Sulfur 19

7. T = 10 K n = 10 4 cm -3 Physics and Chemistry of the Interstellar Medium

8. Helsinki Winter School The Role of Gas Phase Ion – Molecule Reactions - Laboratory Studies Stephan Schlemmer WHAT? Kinetics of ion-molecule reactions radiative association (one example) WHY? Identification of Species (Column Densities) Formation and Destruction HOW? Experimental Techniques (Laboratory work) December 13, 2006

9. Forschergruppe Laboratory Astrophysics

10. Importance of Ion-Molecule Reactions E. Herbst, The Physics and Chemistry of Interstellar MCs (1993) Arrhenius: k(T) = = A exp (-E A /kT) Neutral-Neutral Reactions A  10 -11 cm 3 /s E A  2000 K T MC = 10 K Ion-Molecule Reactions 10 -7 cm 3 /s > A > 10 -9 cm 3 /s E A  0 K Cosmic Ray Ionization Ion-Molecule Reactions Recombination EAEA ReactantsProducts

11. Ion – induced dipole interaction long range forces p b Kinetic energy E = p 2 / 2  Angular momentum L = b p = l h Centrifugal barrier V = + L 2 /(2  r 2 ) V = - q  / r 4 + + + + - - -

12. Ion – induced dipole interaction Rate of Reaction p b Kinetic energy E = p 2 / 2  Angular momentum L = b p = l h Cross section  (E):  (E) = 2  * b db =  b max 2 Rate coefficient: k = T ion-induced dipole: k L = const.

13. Temperature Dependence of Ion-Molecule Reactions M.A. Smith (1994) Langevin Rate Coefficient:

14. Details of Potential Energy Surface Reactants Association Products Transition State E kT Rotational Energy, Zero Point Energy and Fine Structure Energy

15. Details of Potential Energy Surface Reactants Association Products Transition State E kT

16. Low Temperature Collisions in Flow Systems and Traps (state-of-the-art experiments)

18. Isentropic expansion and uniform supersonic flow Laval nozzle and isentropic flow uniform supersonic flow T = 7 – 220 K  = 10 16 – 10 18 cm –3 nozzle throat diameter 3 mm – 5 cm chamber pressure 0.1 – 0.25 mbar max pumping speed  30000 m 3 h -1 Axisymmetric Laval nozzle 50-100 l/min carrier gas (He, Ar) + reagent + precursor Smith, Sims & Rowe, Chem Eur J, 3[12], 1925-1928 (1997 )

19. k(T) A B T 0, p 0 z, t [B] T const. Pulsed Uniform Supersonic Expansion A + B  Products k = (  [B]) -1

20. CRESU: Cinétique de Réaction en Ecoulement Supersonique Uniforme B. Rowe (Rennes), I. Sims (Rennes), M. Smith (Tucson)

21. ln [A] t     z/v ~ 0.1/500 s ~ 200 µs [B]  10 15 cm -3 k  5  10 -12 cm 3 /s Pulsed Uniform Supersonic Expansion A + B  Product d[A]/dt = - k [A] [B] k = (  [B]) -1

22. 22-Pole Low Temperature Ion Trap primary ions detector rf II rf I sapphire 22-pole cold head 10 K shield 50 K

23. Trap Experiment A + B  Products d[A]/dt = - k [A] [B] k = (  [B]) -1 1 ms   100 s 10 8 cm -3  [B]  10 15 cm -3 k  10 -17 cm 3 /s

24. Method: Electrodynamical Trapping

25. Quadrupole22-Pole RF Ion Trap Mechanical Model

26. Trajectories of ions in 22-pole trap f= 17MHz V 0 =20V + m=20u × m=2u

27. f= 17MHz V 0 =20V + m=20u × m=2u Trajectories of ions in 22-pole trap

30. Low Temperature 22 Pole Ion Trap

31. Low Temperature 22 Pole Trap

32. Initial reactions in dense interstellar clouds D. Smith and P. Spanel, Mass Spectrometry Reviews, 14 (1995) 255-278.

33. Forschergruppe Laboratory Astrophysics

35. Initial reactions in dense interstellar clouds D. Smith and P. Spanel, Mass Spectrometry Reviews, 14 (1995) 255-278.

36. Deuteration of H 3 + [ HD] = 1.8x10 12 cm -3 T = 10 K H3+H3+ H2D+H2D+ HDHD D2H+D2H+ HDHD D3+D3+ HDHD k1k1 k2k2 k3k3

37. H3+H3+ H2D+H2D+ H5+H5+ H4D+H4D+ H 3 + + HD  H 2 D + + H 2 [n-H 2 ] = 1.4x10 14 cm -3, [HD]/[H 2 ] = 3*10 -4, T = 10 K 0.002

38. H3+H3+ H2D+H2D+ H5+H5+ H4D+H4D+ H 3 + + HD  H 2 D + + H 2 [p-H 2 ] = 1x10 14 cm -3, [HD]/[H 2 ] = 3*10 -4, T = 10 K 0.15

39. Initial reactions in dense interstellar clouds D. Smith and P. Spanel, Mass Spectrometry Reviews, 14 (1995) 255-278.

40. Example I: Negative Temperature Dependence NH 3 + + H 2  NH 4 + + H Gas Phase Formation of Ammonia NH n + + H 2  NH n+1 + + H n = 0,1,2,3

41. Implications of a barrier along reaction path Arrhenius: k(T) = = A exp (-E A /kT) EAEA ReactantsProducts k T / K 101001000

42. Experiment Theoretical Prediction Negative Temperature Dependence NH 3 + + H 2  NH 4 + + H Herbst et al. J.Chem.Phys. 1991

43. kcal/mol Lowest energy path for NH 3 + + H 2  NH 4 + + H van der Waals binding

44. Negative Temperature Dependence NH 3 + + H 2  NH 4 + + H  k << k L 1 in 10000 collisions leads to reaction  Turnover at 100 K  barrier height 4.8 kcal/mol (2400 K)  Tunneling is a dominant mechanism at low temperatures

45. Example II: Radiative Association CH 3 + + H 2 O  CH 5 O + + h A. Luca, D. Voulot, and D. Gerlich, WDS'02 Proceedings of Contributed Papers, Part II, Safrankova (ed), Matfyzpress, 294-300 (2002) TP5

46. Initial reactions in dense interstellar clouds D. Smith and P. Spanel, Mass Spectrometry Reviews, 14 (1995) 255-278.

48. Results: Formation of protonated methanol

49. Radiative Association AB + + C ABC + A + BC + ~ ~

50. Density Dependence of Association Reaction Radiative k r Ternary k 3

51. Radiative Association: k r Comparison to Statistical Theories

52. Helsinki Winter School The Role of Gas Phase Ion – Molecule Reactions - Laboratory Studies Stephan Schlemmer WHAT? Kinetics of ion-molecule reactions radiative association (one example) WHY? Identification of Species (Column Densities) Formation and Destruction HOW? Experimental Techniques (Laboratory work) December 13, 2006