SESAPS Terahertz Rotational Spectrum of the v5/2v9 Dyad of Nitric Acid * Paul Helminger, a Douglas T. Petkie, b Ivan Medvedev, b and Frank C. De Lucia c a Department of Physics University of South Alabama Mobile, AL b Department of Physics Wright State University Dayton, OH c Department of Physics The Ohio State University Columbus, OH * This work is supported by NASA SESAPS October 20, 2011 Roanoke, VA

SESAPS Outline Introductory remarks Experimental overview Motivation for the study Assigning the THz v 5 /2v 9 Spectrum v 5 /2v 9 Analysis Overall progress on states below 1000 cm -1 Conclusions

SESAPS Microwave Laboratory Terahertz Timeline Duke Microwave Lab paper on Spectroscopy in the THz Region appeared in Applied Physics Letters in Included high resolution measurement of CO rotational transition at THz. THz energy was generated using phase locked 50 GHz klystron and special point contact harmonic multiplier (18 th and 19 th harmonics). In 2007, terahertz capability added to FASSST spectrometer at the Ohio State Microwave Laboratory. Experimental Signal/Noise Ratio of ~1000 allows recording transitions with energies ~1500 cm -1 above ground state. Solid state sources at even higher frequencies are now available in the lab.

SESAPS GHz375GHz

SESAPS InSb detector 1 InSb detector 2 Ring cavity: L~15 m Mylar beam splitter 1 Mylar beam splitter 2 Aluminum cell: length 6 m; diameter 15 cm BWO Magnet Lens Length ~60 cm Stepper motor Lens Stainless steel rails Path of microwave radiation Reference gas cell Glass rings used to suppress reflections FAst Scan Submillimeter Spectroscopic Technique (FASSST) spectrometer

SESAPS THz spectrum of Nitric Acid

SESAPS Motivation Atmospheric interest –Murcray, et. al., 1968, Ballone-borne experiment –Various ir bands from ~ 5  – 25  as well as various mm/submm- wave windows Fundamental spectroscopic interest –Internal rotation From Ken Jucks

SESAPS Vibrational States of HNO 3 kT Our published lower frequency studies include all states below 1225 cm -1  a = 1.98 D  b = 0.88 D a-type  K a = 0,  2  K c =  1,  3 b-type  K a =  1,  3  K c =  1,  3 N OO O H A. Perrin, Spectrochim Acta A 54 (1998) 375 A. Goldman et al., JSQRT 60 (1998) 851

SESAPS Assigning the THz Spectrum of HNO 3 Use existing lower frequency microwave analyses (with measured lines to 600 GHz) to predict the THz spectrum of each vibrational state. Identify lines in the lower range of the THz spectrum that are not too far off. The transitions with the best predictions will generally be the transitions within the J/K range of the lower frequency data. Bootstrap through reanalysis and additional measurements to reach higher J/K transitions and to reach the upper range of the THz spectrum. The v 5 /2v 9 spectrum is very complex. Analysis must include effects due to torsional splitting and fermi and coriolis interactions. Energy levels from infrared data stabilize the fit.

SESAPS Torsional Effects on the Spectrum J+1 0,J+1 J+1 1,J+1 J+1 0,J+1 J 0,J J 1,J J 0,J a-typeb-type R-Branch o   Torsional Splitting 2v MHz V MHz

SESAPS HITRAN’2002–OSU–11 5 Mixing Contour Map and Microwave Data Set  K =  2 interactions are displayed on this figure (Artificial splitting analysis) J = 0 %mixing is 59/41 when including the F o term

SESAPS Internal Axis System (IAS) Hamiltonian I R representation in the A-reduction (z = a, x = b, y = c) SPFIT, SPCAT Programs Developed by Herb Pickett at JPL Rotational Torsional Fermi and C-type Coriolis Interactions

SESAPS HNO 3 - Completed THz Analyses HNO3 StateLower Frequency Data THz DataAnalysis Features v0Data to 831 GHz with J max 74, K a max 57 Data to 1131 GHz with J max 90, K a max 53 v9 (458 cm -1 )Data to 655 GHz with J max 60, K a max 47 Data to 1131 GHz with J max 88, K a max 47 v7 (580 cm -1 )Data to 578 GHz with J max 70, K a max 43 Data to 1131 GHz with J max 86, K a max 47 Terms for perturbation with v6 v6 (646 cm -1 )Data to 657 GHz with J max 67, K a max 44 Data to 1129 GHz with J max 85, K a max 47 Terms for perturbation with v7 v8 (763 cm -1 )Data to 519 GHz with J max 56, K a max 41 Data to 1127 GHz with J max 86, K a max 45

SESAPS HNO 3 – v5/2v9 Dyad HNO3 StateLower FrequencyTHz DataAnalysis Features * v5 (879 cm -1 )Data to 641 GHz with J max 53, K a max 39 Data to 1039 GHz with J max 79, K a max 44 Terms for perturbation with 2v9 2v9 (896 cm -1 )Data to 642 GHz with J max 51, K a max 37 Data to 1039 GHz with J max 82, K a max 43 Terms for perturbation with v5 Analysis includes 2300 infrared energy levels courtesy of Agnes Perrin (For v5: J max 66, K a max 40; for 2v9: J max 62, K a max 38)

SESAPS Conclusions Measurements and analysis of the THz spectrum of nitric acid in the ground state v 0 and excited states v 9, v 7, v 6, and v 8 have been completed. Work on the THz spectrum of the v5/2v9 dyad is in progress. More work is needed. Analysis with both MW and IR data is providing the best results.

SESAPS The end

SESAPS Torsional Splitting Summary StateObserved Splitting in MHz 9 77 Not resolved 9 6 Triplet b b a 316 GHz region Frequency/MHz Signal/au

SESAPS HITRAN’2002–OSU–18 Induced vs. Artificial Splitting Models Classic Fermi resonance term is determinable with torsional splitting measurements InducedArtificial Practical problem with labeling the rotational levels due to the large mixing J = 0 wavefuction percent mixing from the analysis 59/41 (=1.439)

SESAPS Nitric Acid Vibrational States Review article “Recent progress in the analysis of HNO3 spectra” by A. Perrin, Spectrochimica Acta Part A 54 (1998) 375–393.