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Near-Infrared Spectroscopy of H 3 + Above the Barrier to Linearity

Near-Infrared Spectroscopy of H 3 + Above the Barrier to Linearity. Jennifer L. Gottfried Department of Chemistry, The University of Chicago *Current address: U. S. Army Research Laboratory, Aberdeen Proving Ground, Maryland Royal Society Discussion Meeting, January 16, 2005.

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Near-Infrared Spectroscopy of H 3 + Above the Barrier to Linearity

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  1. Near-Infrared Spectroscopyof H3+ Above the Barrier to Linearity Jennifer L. Gottfried Department of Chemistry, The University of Chicago *Current address: U. S. Army Research Laboratory, Aberdeen Proving Ground, Maryland Royal Society Discussion Meeting, January 16, 2005

  2. Introduction to H3+ Geometry of H3+ • Simplest polyatomic molecule • Ground state equilibrium structure is an equilateral triangle: Spectroscopy of H3+ • No allowed rotational spectrum • No discrete electronic spectrum • Vibrational spectroscopy • symmetric stretch n1 • not IR active 3178.36 cm-1 • the doubly degenerate mode n2 • is IR active2521.38 cm-1 • vibrational angular momentum ℓ

  3. 25 years of laboratory spectroscopy of H3+ Jupiter GalacticCenter Saturn & Uranus ISM Oka McCall Gottfried Lindsay & McCall, JMS 210, 60 (2001).

  4. Vibrational Bands 6n26 6n24 3n1+2n2 6n22 2n1+3n2 6n20 n1+ 4n2 5n25 3n1+n2 5n23 5n21 2n1+2n2 4n24 n1+ 3n2 3n1 4n22 4n20 2n1+n2 n1+2n22 n1+2n20 3n23 3n21 2n1 n1+ n2 2n22 2n20 Hot bands Overtones n1 n2 Forbidden transitions n2 fundamental band [T. Oka, Phys. Rev. Lett. 45, 531 (1980)] Combination bands

  5. Motivation for Studying H3+ at High Energies • Astronomical importance • The first overtone (2n20) has been observed in emission in Jupiter, as have hot band transitions from the 3n2 level • 6669 cm-1 in overtone bands • 7993 cm-1 in hot bands [P. Drossart, J. P. Maillard, J. Caldwell et al., Nature (London) 340, 539 (1989).] [E. Raynaud, E. Lellouch, J.-P. Maillard, G. R. Gladstone, et al. Icarus 171, 133 (2004).] • Theoretical importance • Benchmark for first principle quantum mechanics calculations • Comparison between experimental and calculated energy levels  important diagnostic tool

  6. q Barrier to Linearity

  7. Expectation Values (Watson) J=0-2, J=3-5, J=6-10, J=11-15, J=16-20

  8. Burleigh WA-1500 Near-Infrared Spectrometer • 4 passes through cell clockwise • 4 passes through cell counter- • clockwise • Discharge driven at 19 kHz = • velocity modulation • Electro-optic modulator (EOM) • driven at 500 MHz = • frequency modulation • Signal demodulated by double- • balance mixer (DBM) and • lock-in amplifiers (PSD) • external wavemeter, I2 cell • and 2-GHz étalon provide • frequency calibration • continuous coverage from • ~10,650-13,800 cm-1 • 938-725 nm (3 optics sets) J. L. Gottfried, “Near-infrared spectroscopy of H3+ and CH2+” Ph.D. Thesis, University of Chicago, August 2005.

  9. Vibrational Bands 6n26 6n24 3n1+2n2 6n22 2n1+3n2 6n20 n1+ 4n2 5n25 3n1+n2 5n23 5n21 2n1+2n2 4n24 n1+ 3n2 3n1 4n22 4n20 2n1+n2 n1+2n22 n1+2n20 3n23 3n21 2n1 n1+ n2 2n22 2n20 15 new transitions n1 22 new transitions above the barrier to linearity n2 C. F. Neese, C. P. Morong, T. Oka, in progress (see Exhibit). J. L. Gottfried, B. J. McCall, and T. Oka, J. Chem. Phys. 118, 10890 (2003).

  10. Improvement in Sensitivity Sensitivity ~1.5×10-2 Sensitivity ~10-8

  11. Hydrogen Rydberg Transitions • Pure H2 (500 mTorr) discharge • H2* is only interferent • H2 excited by e- bombardment • acquires momentum, usually anion lineshape • Quenched by metastable He* • 10 Torr He added for discrimination

  12. Near-infrared Transitions of H3+ combination long/mid- wavelength optics set: 10,725-10,790 cm-1 (8 lines) midwavelength optics set: 11,019-12,419 (22 lines)

  13. Visible Transitions of H3+ (midwavelength optics set) short wavelength optics set: 12,502-13,677 cm-1 (7 lines)

  14. Importance of Theoretical Calculations Strong vibration-rotation interaction B0 = 43.565 cm-1 C0 = 20.605 cm-1 ζ = - 1 q = - 5.372 cm-1 Oka, Phys. Rev. Lett. 45, 531 (1980).

  15. Observed Spectrum of H3+ 4th u1u2 ℓ DG{P|Q|R}(J,G)u/l J < 4 5th observed lines, predicted lines by Neale, Miller, Tennyson 1996

  16. Röhse, Kutzelnigg, Jaquet, Klopper (RKJK) Cencek, Rychlewski, Jaquet, Kutzelnigg (CRJK) Dinelli, Polyansky, Tennyson (DPT) Jaquet (Jaq02) Alijah, Hinze, Wolniewicz (AHW) Neale, Miller, Tennyson (NMT) Jaquet (Jaq03) Schiffels, Alijah, Hinze (SAH) error < ±0.1 cm-1

  17. Comparison to Theory [Alijah, Hinze, Wolniewicz, Ber. Bunsenges. Phys. Chem. 99, 251 (1995)] [Schiffels, Alijah, Hinze, Mol. Phys. 101, 189 (2003).] [Neale, Miller, Tennyson, Astrophys. J. 464, 516 (1996).] [Alijah, private communication (2003).] [Jaquet, Prog. Theor. Chem. Phys. 13, 503 (2003).] empirical correction for nonadiabatic effects purely ab initio calculation!

  18. Conclusions • Errors in calculated energy levels significantly larger above the barrier to linearity Gottfried, McCall, Oka 2003 Neese, Morong, Oka (in progress)

  19. Conclusions • First principle ab initio theory on H3+ has reached spectroscopic accuracy • only nonadiabatic and QED corrections missing H2:W. Kołos, L. Wolniewicz 1964 – 1975 J. Mol. Spectrosc. 54, 303 (1975) H3+: Schiffels, Alijah, Hinze, Mol. Phys. 101, 175, 189 (2003) Nearly 30 years to progress from a two-particle problem to a three-particle problem!

  20. Future Prospects • Expect to observe an additional 90 transitions of H3+ with current spectrometer

  21. Future Prospects • Continuing climb up energy ladder (6n240, 7n210,…) visible dye laser Improvements in experimental sensitivity needed! Pseudo-low resolution convolution of experimental data[Carrington, Kennedy, J. Chem. Phys.81, 1 (1984)] Energy diagram showing significant energies of H3+ [Kemp, Kirk, McNab, Phil. Trans. R. Soc. Lond. A358, 2403 (2000)]

  22. Acknowledgements • Takeshi Oka • Ben McCall • Chris Neese and Chris Morong • J. K. G. Watson and A. Alijah • National Science Foundation Graduate Research Fellowship • NSF Grants

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