NearInfrared Spectroscopy of H3 Above the Barrier to Linearity

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 active 2521.38 cm-1
• vibrational angular momentum l

3
25 years of laboratory spectroscopy of H3
Jupiter
GalacticCenter
Saturn Uranus
ISM
McCall
Oka
Gottfried
Lindsay McCall, JMS 210, 60 (2001).
4
Vibrational Bands
6n26
3n12n2
6n24
2n13n2
6n22
6n20
n1 4n2
5n25
3n1n2
5n23
5n21
2n12n2
4n24
n1 3n2
3n1
4n22
4n20
2n1n2
n12n22
3n23
n12n20
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

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Barrier to Linearity
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Expectation Values (Watson)
J0-2, J3-5, J6-10, J11-15, J16-20
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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.
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Vibrational Bands
6n26
3n12n2
6n24
2n13n2
6n22
6n20
n1 4n2
5n25
3n1n2
5n23
5n21
2n12n2
4n24
n1 3n2
3n1
4n22
4n20
2n1n2
n12n22
3n23
n12n20
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).
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Improvement in Sensitivity
Sensitivity 1.510-2
Sensitivity 10-8
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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

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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)
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Visible Transitions of H3
(midwavelength optics set)
short wavelength optics set 12,502-13,677 cm-1
(7 lines)
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Importance of Theoretical Calculations
Strong vibration-rotation interaction
B0 43.565 cm-1 C0 20.605 cm-1
? - 1
q - 5.372 cm-1
Oka, Phys. Rev. Lett. 45, 531 (1980).
15
Observed Spectrum of H3
4th
u1u2 l
DGP Q R (J,G )u/l J lt 4
5th
observed lines, predicted lines by Neale, Miller,
Tennyson 1996
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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 lt 0.1 cm-1
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Comparison to Theory
Neale, Miller, Tennyson, Astrophys. J. 464, 516
(1996).
Alijah, Hinze, Wolniewicz, Ber. Bunsenges.
Phys. Chem. 99, 251 (1995)
Schiffels, Alijah, Hinze, Mol. Phys. 101, 189
(2003).
Jaquet, Prog. Theor. Chem. Phys. 13, 503 (2003).
Alijah, private communication (2003).
purely ab initio calculation!
empirical correction for nonadiabatic effects
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Conclusions

• Errors in calculated energy levels significantly
  larger above the barrier to linearity

Gottfried, McCall, Oka 2003
Neese, Morong, Oka (in progress)
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Conclusions

• First principle ab initio theory on H3 has
  reached spectroscopic accuracy
• only nonadiabatic and QED corrections missing
• H2 W. Kolos, 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!
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Future Prospects

• Expect to observe an additional 90 transitions of
  H3 with current spectrometer

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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. A
358, 2403 (2000)
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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