MODERATE RESOLUTION JET COOLED CAVITY RINGDOWN SPECTROSCOPY OF THE A STATE OF NO 3 RADICAL Terrance J. Codd, Ming-Wei Chen, Mourad Roudjane and Terry A. Miller The Ohio State University ~

Introduction NO 3 is the primary oxidant in the night-time troposphere Has three low lying electronic states: X 2 A 2, A 2 E  and B 2 E Significant Jahn-Teller coupling is expected in both excited electronic states 1 A well resolved spectrum of the A state vibronic structure would provide information to determine the strength of this coupling     1. W. Eisfeld, K. Morokuma, J. Chem. Phys. 114 (2001) M. Okumura, J. F. Stanton, A. Deev, J. Sommar, Physica Scripta 73 (2006)

NO 3 A State: Previous Experiments Ambient CRDS: Deev et al. 1 Made several assignments and estimated origin Broad rotational contours and hot bands complicated the analysis Ne matrix: Jacox and Thompson 2 Several additional assignments Studied several isotopes Satellite bands from matrix interactions were present 1.A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, (2005) 2.M. Jacox, W. Thompson J. Phys. Chem. A 114, (2010) ~

≈ ≈ ≈ ≈ NO 3 : Vibronic Structure Red arrows show vibronically allowed transitions Vibronic structure here assumes linear and quadratic JT coupling are present

A =σN l Photo- diode τ0τ0 c L )/ ( R1 - = τ abs σ Nlσ Nl + = cL)/( R1 - ( )  abs Time Intensity 00 A = L/(cτ abs )- L/(cτ 0 ) Sensitivity of Technique If R = 99.99% and L = 67cm then τ 0 = 22.3 μs L eff = 6.7 km ∼ 4.16 Miles l = 5 cm l eff = 0.5 km l L Cavity Ringdown Spectroscopy

Mod-Res Jet Cooled Apparatus Nd:YAG 20 Hz Sirah Dye Laser H 2 Raman Cell Filters 1 st or 2 nd Stokes 2-10 mJ mJ mJ 20 m Fiber Optic ~2 GHz FWHM N 2 O 5 in Neon NO 2 + NO 3 PD

Spectrum Shown is our jet cooled spectrum from 7550 cm -1 to 9750 cm -1. a.u.

Shown in the red is ambient data from Okumura’s lab Spectrum a.u. Okumura Ours

Spectrum a.u. Okumura Ours

We used the Deev 1 assignments as a starting point Additional assignments can be made following Jacox’s 2 work A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, (2005) 2.M. Jacox, W. Thompson J. Phys. Chem. A 114, (2010) Assignments a.u.

Analysis: Harmonic Using these assignments and the origin frequency from Deev it is possible to predict transition frequencies of unassigned bands Assignments can be made and then band frequencies and anharmonic constants can be fit As a first approximation, use harominic oscillator energy expressions with lowest order anharmonic terms

Analysis: Harmonic a.u.

Analysis: Harmonic The unassigned band lies at cm -1 ( cm -1 from origin) and the other at cm -1 (516.2 cm -1 to the blue of this band) The 3 mode has been predicted to be 1602 cm -1 using state-averaged CASSCF 1 The higher frequency band is consistent with a combination band with Eisfeld, W. Morokuma, K, J. Chem. Phys. 144, 9430, (2001)

Analysis: Simple Harmonic a.u. All units are in wavenumbers Fitted Frequencies Anharmonic Constants v v v v v v30 v v RMS Error: 6.42 cm -1

Analysis: Including Jahn-Teller A very simple analysis does a surprisingly good job of describing our spectra However, ab initio calculations indicate that the JT coupling in the A state should be strong A new version of SOCJT has been written which can include non-degenerate modes and bilinear coupling ,  exe, D, K, and bilinear coupling (b) can be fit NO 3 has only 4 modes so it is possible to do a global fit

Analysis: Including Jahn-Teller The initial fit results are shown below The RMS error is cm -1. If we disregard two bands involving ν 1 and ν 2 the RMS error drops to 3.89 cm -1. JT constants are effectively 0. ModeFrequencyAnharmonicDK Bilinear Coupling Constant

1 4 Combination Bands Combination bands of 1 and 4 have a distinct ‘split-parallel’ band contour Based on symmetry considerations they should have a parallel band type. The splitting is as large as 26 cm -1 but is smaller for most bands This is unique to the 1 4 combination bands and is seen in all of them a.u.

Spectrum Shown is our jet cooled spectrum from 7550 cm -1 to 9750 cm a.u.

Conclusions Little or no evidence of strong JT coupling in the 4 mode Spectrum is well described by even a very simple analysis Fitting our spectrum including JT terms does not significantly improve our fit and More work needs to be done to understand the nature of the splitting observed in the 1 4 combination bands

Acknowledgements Terry Miller Miller Group Neal Kline Rabi Chhantyal-Pun Mourad Roudjane Takashige Fujiwara Dianping Sun Ming-Wei Chen  Mitchio Okumura for allowing the use of his data NSF - $$$ You for your attention!  Currently at University of Illinois Urbana-Champaign