1. DEVELOPMENT OF BROAD RANGE SCAN CAPABILITIES WITH JET COOLED CAVITY RINGDOWN SPECTROSCOPY Terrance Codd, Ming-Wei Chen, Terry A. Miller The Ohio State University

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

3. Comparison of CRDS Methods for A-X NO 3  HR JC-CRDS  Specs  Radiation 100-250 MHz FWHM  Rotational temps 15-30 K  Benefits  Resolved transitions can be used to accurately determine rotational and spin rotational constants and orientation of TDM  Drawbacks  Radiation difficult to produce and scans very time consuming  RT CRDS  Specs  ~2 GHz FWHM  Deev et al, 4.5 GHz  Ambient temperatures  Benefits  Can quickly scan very broad ranges and radiation is easy to generate  Drawbacks  Higher rotational temperature leads to congestion of transitions making assignment difficult. ~~ Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, 2243051 (2005) Jacox, M; Thompson, W. E.; J. Chem. Phys.; 122, 224305 (2005)

4. Combining Mod Res/Jet Cooling  Want to combine some of the benefits of moderate resolution radiation sources (broad range scan capabilities and ease of use) with the benefits of the jet cooled system (rotationally cold samples)  Goal: couple moderate resolution radiation with JC- CRDS

5. Mod-Res Jet Cooled CRDS  Fiber Optic works very well. Roughly 90% efficient transmission of IR Nd:YAG 20 Hz Sirah Dye Laser H 2 Raman Cell Filters 1 st or 2 nd Stokes 2-10 mJ/ 650 - 700 mJ75 - 115 mJ 20 m Fiber Optic Collimator ~2 GHz FWHM N 2 O 5 in First Run Neon NO 2 + NO 3 PD

6. Previous CRDS of NO 3  Previous CRDS spectra of A-X transition of NO 3 have been done in the Okumura lab under ambient conditions. High rotational temps make band assignments difficult.  No good assignment of the  3 band 401401 201201 301301 402402 101401101401 101201101201 403403 101402101402 A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, 2243051 (2005) ~~

7. Comparison To Room Temp Ambient NO 3 data courtesy of M. Okumura

8. Comparison To Room Temp Ambient NO 3 data courtesy of M. Okumura

9. NO 3 Radical 4 0 1 Band  See intensity cut by ~2/3 compared to HR  Can resolve rotational structure but not individual transitions. TD07

10. Characterizing Method  Have lower signal to noise ratio than with high- resolution radiation  Reduction in signal probably due to the fact that the transitions being observed have a much narrower linewidth than the radiation  Signal intensity is limited by both intensity and density of transitions  Increase in noise probably caused by using radiation which is much broader than FSR of cavity  Means we span a number of longitudinal cavity modes  Consistent with our experience on RT-CRDS  Provides sufficient sensitivity for weak transitions

11. Making Assignments  We used these assignments as a starting point to get good fundamental frequencies for the vibrational modes. 401401 201201 301301 402402 101401101401 101201101201 403403 101402101402 A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, 2243051 (2005) 401401 201201 402402 101401101401 101201101201 403403 101402101402

12. Predicting Transitions  To aid in the assignment of other transitions a set of predicted transitions were calculated.  Used pure harmonic approximations as a first guess based on fundamental frequency.  Made assignments based on that and then fit anharmonic constants and frequencies.  Done with all possible modes combinations NOT including any quanta of excitation in  3.

13. Predicted Assignments 401401 402402 201401201401 101401101401 201201 101101 202202

14. 403403 201402201402 201403201403 101402101402 101403101403 203203 101401101401 202401202401 101201401101201401 102401102401 102102 101202101202 103103 102201102201 404404

15. 203401203401 102402102402 201404201404 102403102403 203402203402

16.  3 Assignment  Most prominent unassigned transition in the lower frequency range is the weak parallel band at 8753 cm -1. This is 1689 cm -1 from the origin.  Eisfeld and Morokuma *1 have calculated the frequency of the  3 band to be 1602 cm -1. Previous assignment by Deev *2 for  3 was 300-400 cm -1 away from the predicted frequency and did not have parallel band contour.  Based on the contour and the predicted frequency we assign this to the 3 0 1 band. 1. W. Eisfeld, K. Morokuma, J. Chem. Phys. 114, 9430 (2001) 2. A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, 2243051 (2005) 403403 201402201402 201403201403 101402101402 101403101403 203203 101401101401 202401202401 101201401101201401 102401102401 102102 101202101202 103103 102201102201 404404

17. Other Work  Wanted to use this apparatus to investigate other molecules as well  Hydroxy Propyl Peroxy radical is being studied on the RT-CRDS system  A jet cooled spectrum could aid in the assignment of some of the low frequency transitions observed

18. Hydroxy Propyl Peroxy  Entire Jet-Cooled spectrum was done in ~2 hours WJ11 000000

19. Conclusion  We have developed a moderate resolution jet cooled cavity ringdown spectrometer capable of quickly obtaining broad range scans with good sensitivity.  We have obtained spectra of the A-X transition of NO 3  Almost all of the cold vibronic spectrum has been assigned including the 3 0 1 band.  Additional broadband structure has been revealed which is coincident with vibronically forbidden transitions  Splitting in υ 1 υ 4 combination bands have been observed  Ongoing analysis should provide more insight into the Jahn-Teller effect and vibronic coupling in the A state of NO 3. ~~ ~

20. Acknowledgments  Dr. Terry Miller  Miller Group Members  Ming-Wei Chen  Gabriel Just*  Rabi Chhantyal-Pun  Neal Kline  Jin-Jun Liu  Phillip Thomas ǂ  NSF-$$$$$  You for your attention! *Currently at Lawrence Berkeley National Lab, Berkeley California ǂ Currently at Leiden Institute of Chemistry, Netherlands

21. Assignments 401401 402402 403403 201401201401 201402201402 201403201403 101401101401 101402101402 101403101403 201201 203203 101401101401 301301 202401202401 203401203401 102402102402 203402203402 102403102403 201404201404 101201401101201401 102401102401

22.  1 -  4 Progression  Shown are some of the  1 -  4 bands  All have the same ‘doubled- parallel’ band contour  We are currently exploring the cause of this 101401101401 101402101402 102402102402

23. Anharmonicity Parameters  Used expansion shown below  Fitted constants shown below v1758.1863 Anharmonic Constants v2678.1125v1-5.18798 v31689v2-4.75345 v4533.0631v30 Origin7064v4-0.11676 Cross Anharmonic v1v217.91164 v1v41.996614 v2v43.554414

24. IR Beam 9 mm -HV radical densities of 10 12 - 10 13 molecules/cm 3 (10 mm downstream, probed) rotational temperature of 15 - 30 K plasma voltage ~ 500 V, I  1 A (~ 400 mA typical), 100 µs length dc and/or rf discharge, discharge localized between electrode plates, increased signal compared to longitudinal geometry Previous similar slit-jet designs: D.J. Nesbitt group, Chem. Phys. Lett. 258, 207 (1996); R.J. Saykally group, Rev. Sci. Instrum. 67, 410 (1996); T. A. Miller group, Phys. Chem. Chem. Phys. 8, 1682 (2006). 5 cm 5 mm 10 mm Electrode Viton Poppet N 2 O 5 in First Run Neon Slit Jet/Discharge NO 2 + NO 3

25. Electronic/Vibronic Structure  Normal electronic selection rules:  n  µ  m  a  Where n and m are electronic states, µ is the electronic transition dipole moment and  a is the totally symmetric representation  Hertzberg-Teller (vibronic coupling):  n  µ  vib  m  a  Where  vib is the symmetry of the excited state vibrational mode M. Okumura J. F. Stanton, A. Deev and J. Sommar, Phys. Scr., 73, C64 (2006). µ x = µ y =  x,y = e’: Perpendicular Bands µ z =  z = a 2 ’’: Parallel Bands