Near-Infrared Spectroscopyof H3

+ Above the Barrier to Linearity

Jennifer L. GottfriedDepartment of Chemistry, The University of Chicago

*Current address: U. S. Army Research Laboratory, Aberdeen Proving Ground, Maryland

Royal Society Discussion Meeting, January 16, 2005

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 1

not IR active 3178.36 cm-1

the doubly degenerate mode 2

is IR active 2521.38 cm-1

vibrational angular momentum ℓ

McCall

25 years of laboratory spectroscopy of H3

+

Jupiter

ISM

GalacticCenter

Saturn &

Uranus

Oka Gottfried

Lindsay & McCall, JMS 210, 60 (2001).

0

2000

4000

6000

8000

10000

12000

14000En

ergy

(cm

-1)

23

22

23

2

20

22

21

20

24

21

25

1

1+2

1+2

1

1

1+2

1+2

1+220 2

2

24 2

6

1+ 2

1+20

1+22

1+ 2

1+ 2

Vibrational Bands

Hot bands

Overtones

Forbidden transitionsCombination

bands

2 fundamental band

[T. Oka, Phys. Rev. Lett. 45, 531 (1980)]

Motivation for Studying H3+ at High

Energies Astronomical importance

The first overtone (22 0) has been observed in emission in Jupiter, as have hot band transitions from the 32 level

6669 cm-1 in overtone bands

7993 cm-1 in hot bands

Theoretical importance

Benchmark for first principle quantum mechanics calculations Comparison between experimental and calculated energy levels important diagnostic tool

[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).]

Barrier to Linearity

Expectation Values (Watson)

J=0-2, J=3-5, J=6-10, J=11-15, J=16-20

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)

Near-Infrared Spectrometer

BurleighWA-1500

J. L. Gottfried, “Near-infrared spectroscopy of H3+ and CH2

+”Ph.D. Thesis, University of Chicago, August 2005.

0

2000

4000

6000

8000

10000

12000

14000En

ergy

(cm

-1)

23

22

23

2

20

22

21

20

24

21

25

1

1+2

1+2

1

1

1+2

1+2

1+220 2

2

24 2

6

1+ 2

1+20

1+22

1+ 2

1+ 2

Vibrational Bands

22 new transitions above the barrier to

linearityJ. L. Gottfried, B. J. McCall, and T. Oka,

J. Chem. Phys. 118, 10890 (2003).

15 new transitions15 new transitions

C. F. Neese, C. P. Morong, T. Oka,in progress (see Exhibit).

Improvement in Sensitivity

Sensitivity ~1.5×10-2

Sensitivity ~10-8

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

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)

Visible Transitions of H3+

short wavelength optics set:12,502-13,677 cm-1 (7 lines)

(midwavelength optics set)

Importance of Theoretical Calculations

B0 = 43.565 cm-1

C0 = 20.605 cm-1

q = - 5.372 cm-1

Oka, Phys. Rev. Lett. 45, 531 (1980).

ζ = - 1

Strong vibration-rotation interaction

Observed Spectrum of H3+

12 ℓG{P |Q |R } (J,G )u/l

J < 4

4th

5th

observed lines, predicted lines by Neale, Miller, Tennyson 1996

Röhse, Kutzelnigg, Jaquet,Klopper (RKJK)

Cencek, Rychlewski, Jaquet, Kutzelnigg

(CRJK)

Dinelli, Polyansky, Tennyson (DPT)

Jaquet (Jaq02)Alijah, Hinze, Wolniewicz

(AHW)

Neale, Miller,

Tennyson (NMT)

Schiffels, Alijah, Hinze

(SAH)

Jaquet (Jaq03)

error < ±0.1 cm-1

[Neale, Miller, Tennyson, Astrophys. J. 464, 516 (1996).][Jaquet, Prog. Theor. Chem. Phys. 13, 503 (2003).]

[Alijah, Hinze, Wolniewicz, Ber. Bunsenges. Phys. Chem. 99, 251 (1995)]

[Schiffels, Alijah, Hinze, Mol. Phys. 101, 189 (2003).][Alijah, private communication (2003).]

Comparison to Theory

purely ab initio calculation!empirical correction for nonadiabatic effects

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

Conclusions

Neese, Morong, Oka (in progress)Neese, Morong,

Oka (in progress)

Gottfried, McCall, Oka 2003Gottfried, McCall, Oka 2003

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)

Conclusions

Nearly 30 years to progress from a two-particle problem to a three-particle

problem!

Expect to observe an additional 90 transitions of H3

+ with current spectrometer

Future Prospects

Continuing climb up energy ladder (6240, 72

1 0,…)

Future Prospects

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)]

Improvements in experimental sensitivity

needed!

visible dye laser

Takeshi Oka Ben McCall Chris Neese and Chris Morong

J. K. G. Watson and A. Alijah

National Science Foundation Graduate Research Fellowship

NSF Grants

Acknowledgements