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

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

Comparison of CRDS Methods for A-X NO 3  HR JC-CRDS  Specs  Radiation MHz FWHM  Rotational temps 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, (2005) Jacox, M; Thompson, W. E.; J. Chem. Phys.; 122, (2005)

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

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/ mJ mJ 20 m Fiber Optic Collimator ~2 GHz FWHM N 2 O 5 in First Run Neon NO 2 + NO 3 PD

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 A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, (2005) ~~

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

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

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

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

Making Assignments  We used these assignments as a starting point to get good fundamental frequencies for the vibrational modes A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, (2005)

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.

Predicted Assignments

 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 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 band. 1. W. Eisfeld, K. Morokuma, J. Chem. Phys. 114, 9430 (2001) 2. A. Deev, J. Sommar, M. Okumura J. Chem. Phys. 122, (2005)

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

Hydroxy Propyl Peroxy  Entire Jet-Cooled spectrum was done in ~2 hours WJ

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 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. ~~ ~

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

Assignments

 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

Anharmonicity Parameters  Used expansion shown below  Fitted constants shown below v Anharmonic Constants v v v31689v v v30 Origin7064v Cross Anharmonic v1v v1v v2v

IR Beam 9 mm -HV radical densities of molecules/cm 3 (10 mm downstream, probed) rotational temperature of 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

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