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
22
Embed
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. - PowerPoint PPT Presentation
This document is posted to help you gain knowledge. Please leave a comment to let me know what you think about it! Share it to your friends and learn new things together.
Transcript
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