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Helsinki Winter School Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures

Helsinki Winter School Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures S. Schlemmer WHY? Origin of Deuterium Fractionation How? Experimental Methods What? The key reactions: H 3 + + HD H 2 D + + H 2 Other Primary Deuteration Routes CH n + , C 3 H n +.

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Helsinki Winter School Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures

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  1. Helsinki Winter School Deuterium Fractionation and Ion-Molecule Reactions at Low Temperatures S. Schlemmer WHY?Origin of Deuterium Fractionation How? Experimental Methods What?The key reactions: H3+ + HD H2D+ + H2 Other Primary Deuteration Routes CHn+, C3Hn+ December 14, 2006 Role of Nuclear Spin? Predictive Rules?

  2. Deuterated Moleculesin Interstellar Medium H2D+ Cosmic [D]/[H] ~ 1.5·10-5 D2H+ Isotope Enrichment [AD]/[AH] ~ 0.1 Deuteriumreservoir [HD]/[H2] ~ 3.0·10-5

  3. Deuterated Molecules in Interstellar Medium

  4. Deuterated Molecules in Interstellar Medium

  5. H3+ + HD H2D+ + H2 + 220 K CH3+ + HD CH2D+ + H2 + 375 K AH AD C2H2+ + HD C2HD+ + H2 + 550 K Primary Deuteration Reactions E DE Reactants Products

  6. Isotopic Fractionation HD H3+ H2D+ H2 S(T) = kf/kb [HD]/[H2] 3*10-4 T 10 K [H2D+]/[H3+] ~ 106

  7. HD H2D+ H2 Isotopic Fractionation H, D, HD, H2 e- H3+ M MD+ , MH+ Equilibrium [H2D+]/[H3+] = S(T) [HD]/[H2] S(T) = kf/(kb + a fe- + kM fM)

  8. Isotopic Fractionation HD H3+ H2D+ H2 S(T) = kf/kb S(T) = kf/(kb + a fe- + kM fM)

  9. Astrophysical Observations N2H+ C18O visual extinction or “dust density” (gray scale) toward the western core of the IC 5146 Bergin et al. The Astrophysical Journal, 557:209-229, 2001

  10. H3+ 22 10 100 K 11 0 K X 00 p-H3+ o-H3+ E Lowest energy levels of H3+

  11. H3+ + HD H2D+ +H2 22 10 100 K 11 0 K X 00 110 111 101 000 p-H3+ o-H3+ p-H2D+ o-H2D+

  12. H3+ + HD H2D+ +H2 22 10 100 K 11 o-H2 0 K X 00 110 111 101 000 p-H3+ o-H3+ p-H2D+ o-H2D+

  13. H3+ + HD H2D+ +H2 22 10 100 K 11 o-H2 0 K X 00 110 111 101 000 p-H3+ o-H3+ p-H2D+ o-H2D+

  14. o-H2 o-H2 X Para – Ortho Conversion scrambling p-H2D+ o-H2D+ E/K 400 300 200 p-H2 100 single Quantum State Governs Deuterium Chemistry? p-H2 0

  15. Laser Induced Reactions Spectroscopy with 1000 Ions

  16. H3+ + HD H2D+ +H2 10 100 K 11 0 K X 00 110 111 101 000 p-H3+ o-H3+ p-H2D+ o-H2D+ Reaction hn

  17. FELIX: Free Electron Laser for Infrared eXperiments typical parameters: wavelength: 40 cm-1 to 2200 cm-1 tunable 3rd harmonic > 2200 cm-1 rate: up to 10Hz repetition with microstructure power: ~ 25mJ/pulse at user station resolution: ~0.5% FWHM

  18. LIR-Experiments with FELIX H2D+ + n-H2 p-H2D+ o-H2D+

  19. Laser for LIR of H2D+ FELIX: Range: 50-3300 cm-1 Power: 10Hz, ~200mW Resolution: 0.5% FWHM Agilent diode lasers: 6100-6600 and 6750-7300 cm-1 cw, ~5mW narrow linewidth Düsseldorf OPO (S. Schiller): 2600-3200 cm-1 cw, ~50mW narrow linewidth

  20. search for lines with help of ab initio calculations high-accuracy ab initio calculations for (deuterated) H2+, H3+ : • non-Born-Oppenheimer potentials • relativistic corrections • radiative correction (HD+, Moss 1993) • accuracy better than 0.1cm-1 for H2D+ , 0.001cm-1 for HD+ Jonathan Tennyson: transitions between 0 and 7200 cm-1 for H2D+ and D2H+ , H3+ list available on www

  21. + Spectroscopic results for H2D+ TDoppler=(27±2)K

  22. + Spectroscopic results for H2D+

  23. + Spectroscopic results for D2H+

  24. Comparison Exp-Calc

  25. Comparison Exp-Calc

  26. + present LIR studies of H2D+ • (relative) B coefficients • state-specific reaction rate coefficients • rotationally inelastic rate coefficients • radiative lifetimes • population of four lowest rotational levels

  27. + relative B coefficients B1 B2 signal~B·pop·P·k* conclusions: 1) ab initio predicted (relative) B coefficients reliable 2) reaction probability independent of rovib. overtone excitation

  28. + state-specific reaction rate coefficients every excited H2D+ ion converted to H3+: k*=kc

  29. + rotationally inelastic rate coefficients Repopulation via rotationally. inelastic collisions with H2

  30. + rotationally inelastic rate coefficients conclusion: inelastic collisions ki ~ 10-11 cm3s-1 ~ kc/100

  31. + laser power dependence

  32. + radiative lifetimes result: τeff≈ (70±20)ms

  33. [H3+] pop ~ B ·P rotational level populations of H2D+ 13% 12% TDoppler=(27±2)K 30% Trot,para=(27±2)K 45%

  34. Understanding Deuterium Fractionation? ! Measurement of Rotational Population ! Enhancement of o-H2D+ !? Understanding spectroscopy !? Observation of ortho/para H2D+ ? Heating of H2D+ ? Use of p-H2

  35. H3+ + HD  H2D+ + H2 [n-H2] = 1.4x1014 cm-3, [HD]/[H2] = 3*10-4, T = 10 K H3+ H5+ 0.002 H2D+ H4D+ Gerlich, Herbst and Roueff, Planetary and Space Science 50, 1291 (2002)

  36. Important Questions Role of Nuclear Spin? Role of Dynamics? conservation laws (energy, angular momentum, …) Experiment / Theory / Modelling ?

  37. Potential Energy Surface of H5+ + 2900 1 2 3 ≈ 1500 Hop Rotation 50 1 2 0 3 1 2 3 Xie, Braams and Bowman, J. Chem. Phys. 122, 224307 (2005)

  38. Acknowledgement Dieter Gerlich, Oskar Asvany, Edouard Hugo Düsseldorf: Stefan Schiller Frank Müller Andreas Wicht FELIX:Britta Redlich

  39. Para-H2 Generator

  40. Para-H2 Generator

  41. Astrophysical Observations N2H+ C18O visual extinction or “dust density” (gray scale) toward the western core of the IC 5146 Bergin et al. The Astrophysical Journal, 557:209-229, 2001

  42. van Dishoeck et al.: ISO-SWS grating spectrum Gas - Solid state - ice features

  43. ISO - Observations E.F. van Dishoeck Faraday Discussions 109 Chemistry and Physics of Molecules and Grains in Space

  44. CRYOPAD CRYOgenicPhotoproduct Analysis Device FTIR spectrometer QMS

  45. Source Spectrometer Gas analyse Absorption Detectie Detection gas gas CRYOPAD: IR-Spectroscopy Design Principle

  46. Sample(not seen) FTIR SpectrometerSource Detector

  47. 13 K 40 K 50 K 60 K 65 K 70 K 75 K 80 K 85 K CRYOPAD: IR-spectra of CO-ice CO CO2

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