NIR OFFAXIS ICOS SPECTRUM OF THE NITRATE RADICAL: DOES THE VIBRATIONLESS 2E STATE OF NO3 UNDERGO STA

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NIR OFF-AXIS ICOS SPECTRUM OF THE NITRATE
RADICAL DOES THE VIBRATIONLESS Ã2E? STATE OF NO3
UNDERGO STATIC JAHN-TELLER DISTORTION?

• David J. Robichaud

Kana Takematsu and Mitchio Okumura California
Institute of Technology
Pin Chen and Herbert Pickett Jet Propulsion
Laboratory, California Institute of Technology
John F. Stanton University of Texas
WJ10
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Electronic States of NO3
15 089 cm-1

• B 2E? well studied spectrum is broadened by
  vibronic interactions

B 2E'
Jahn-Teller active

• Ã2E? only 3 expt. studies to date, vibronic
  bands can be rotationally resolved

7 060 cm-1
A 2E?
forbidden

• X 2A2? only recently confirmed D3h geometry
  uncertainty in the fundamental assignments

X 2A'2
D3h geometry
What is the nature of the JT effect in NO3? ?
Spectroscopy of the Ã2E? ? X2A2'
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Jahn-Teller Effect in the Ã2E? state

• Eisfeld and Morokuma
• CASSCF, MRCISD, MRCIQ
• JT Stabilization energy 2000 - 3000 cm-1
• Psuedo-rotation barrier 800-1000 cm-1
• Distorted geometry static distortion
• Symmetric geometry dynamic distortion

2B1 minima
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Full A 2E? ? X 2A2?? Absorption SpectrumDeev,
Sommar, and Okumura, JCP 2005

• Over 50 vibronic bands detected from 6500-11000
  cm-1
• Weak bands ? lt 10-20 cm2
• Strong evidence of Jahn-Teller effect

?4 progression 539 cm-1 519
cm-1 547 cm-1
0.2 cm-1 resolution
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The ?4 Asymmetric Bend (e ?) Vibration JT-Active
Mode
Hirota 1998
Rotationally assigned to a D3h symmetric top
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The ?4 Asymmetric Bend (e ?) Vibration JT-Active
Mode
Hirota 1998
Rotationally assigned to a D3h symmetric top
Deev 2005
Contour analysis suggests D3h excited state
geometry in several bands
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The ?4 Asymmetric Bend (e ?) Vibration JT-Active
Mode
Hirota 1998
Rotationally assigned to a D3h symmetric top
Deev 2005
Contour analysis suggests D3h excited state
geometry in several bands
Is the NO3 A state a case of dynamic distortion?
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Herzberg-Teller Selection Rules limit vibronic
levels that are seen

• 41 E? ? e? A1? ? A2? ? E?

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Herzberg-Teller Selection Rules limit vibronic
levels that are seen
ALLOWED

• 41 E? ? e? A1? ? A2? ? E?

FORBIDDEN from ground state v0
level Off-diagonal JT rotational terms More
asymmetry expected
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Herzberg-Teller Selection Rules limit vibronic
levels that are seen
ALLOWED

• 41 E? ? e? A1? ? A2? ? E?

FORBIDDEN from ground state v0
level Off-diagonal JT rotational terms More
asymmetry expected

• 40 E?

The more distorted E? levels are dark
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Detection of the v0 level via the hot band
Deev 2005
A 2E?
D3h or C2v?
368cm-1
X 2A'2
D3h

• Contour analysis suggests v0 has asymmetric
  geometry
• Rotational structure needs to be resolved

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Diode Laser Detection of NO3 A ? X Spectrum
byIntegrated Cavity Output Spectroscopy

• ICOS cw-diode laser, cavity enhanced technique
• Direct absorption method
• New Focus diode laser
• Sensitivity 10-8 /pass
• Resolution 0.002 cm-1

N2O5 ? NO3 NO2 PNO3 1 x 1013 5 x 1014
/cc Ptot 7 Torr
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ICOS Spectrum of the 41 band
0
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Simulations
EOMIP (Stanton)
Symm top
data
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Preliminary Observations on 41 Band
0

• Evidence that symmetry is broken in v0 level
• High density of lines compared to previous v4
  spectrum of Hirota et al (1998) assigned to D3h
  upper state
• Contour analysis inconsistent with D3h geometry
  in upper level
• Complications
• Lower 41 state (368 cm-1) has not been
  rotationally resolved Coriolis coupling, PJT
  effects present
• Hot band spectra recorded at higher temperatures
  have better S/N but are much more congested

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Future Work

• Rotational analysis of the spectrum using SPFIT
• Program is general enough to allow for fitting of
  spectra to a Jahn-Teller Hamiltonian of arbitrary
  order
• Hindered Rotor basis set is more appropriate for
  intermediate level of coupling than free rotor or
  D3h
• Comparison with ab initio EOMIP calculations
• Stanton (UT Austin)
• Adiabatic surface and nonadiabatic couplings

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Thanks

• Prof. Jaron Hansen (BYU)
• Okumura Group
• JPL Spectroscopy Group
• P. Chelin, N. Ibrahim, C. Fellows, J. Orphal
  (CNRS-LISA)
• NASA UARP

Reminder, check out Stanton Talk Tomorrow
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The n2 Umbrella Vibration A JT-Inactive Mode