Experimental Line Parameters of High-J Transitions in the O 2 A-band Daniel K. Havey and Joseph T. Hodges National Institute of Standards and Technology David A. Long and Mitchio Okumura California Institute of Technology Charles E. Miller Jet Propulsion Laboratory

Motivation Photo: NASA K. Tilford, M. Hoster, P.M. Florian, R.C. Forrey, Phys. Rev. A 69 (2004) The O 2 A-band is important in remote sensing Earth’s atmosphere. (1)Exploits the known concentration of O 2 to obtain path lengths (2)Also used to obtain optical properties of clouds and aerosols Spectroscopy of high-J transitions is interesting and can be important to dynamics. (1)How do experimental and theoretical J- dependence of line intensities differ? (2)How well do existing spectroscopic databases (HITRAN) extrapolate at higher J?

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) K.J. Ritter and T.D. Wilkerson, J. Mol. Spec. 121 (1987) 1. Previous Work on the A-band: P-Branch Line Intensities

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) (2)Schermaul and Learner – FTIR (1999) R. Schermaul and R.C.M. Learner, J. Quant. Spec. Rad. Trans. 61 (1999) 781

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) (2)Schermaul and Learner – FTIR (1999) (3)Brown and Plymate – FTIR (2000) L.R. Brown and C. Plymate, J. Mol. Spec. 199 (2000) 166 Previous Work on the A-band: P-Branch Line Intensities

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) (2)Schermaul and Learner – FTIR (1999) (3)Brown and Plymate – FTIR (2000) (4)Yang et al. – ICLAS (2000) S.F. Yang, M.R. Canagaratna, S.K. Witonksy, S.L. Coy, J.I. Steinfeld, R.W. Field, A.A. Kachanov, J. Mol. Spec. 201 (2000) 188 Previous Work on the A-band: P-Branch Line Intensities

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) (2)Schermaul and Learner – FTIR (1999) (3)Brown and Plymate – FTIR (2000) (4)Yang et al. – ICLAS (2000) (5)Robichaud et al. – FS-CRDS (2008) D.J. Robichaud, J.T. Hodges, P. Masłowski, L.Y. Yeung, M. Okumura, C.E. Miller, L.R. Brown, J. Mol. Spec. 251 (2008) 27 Previous Work on the A-band: P-Branch Line Intensities

S ref = HITRAN 2004 (1)Ritter and Wilkerson – Dye Laser Absorption Spectroscopy (1987) (2)Schermaul and Learner – FTIR (1999) (3)Brown and Plymate – FTIR (2000) (4)Yang et al. – ICLAS (2000) (5)Robichaud et al. – FS-CRDS (2008) (6)Predoi-Cross et al. – FTIR (2008) A. Predoi-Cross, K. Harnbrook, R. Keller, C. Povey, I. Schofield, D. Hurtmans, H. Over, G.C. Mellau, J. Mol. Spec. 248 (2008) 85 Previous Work on the A-band: P-Branch Line Intensities

Previous Work on the A-band: Broadening Parameters L.R. Brown and C. Plymate, J. Mol. Spec. 199 (2000) 166 S.F. Yang, M.R. Canagaratna, S.K. Witonksy, S.L. Coy, J.I. Steinfeld, R.W. Field, A.A. Kachanov, J. Mol. Spec. 201 (2000) 188 D.J. Robichaud, J.T. Hodges, P. Masłowski, L.Y. Yeung, M. Okumura, C.E. Miller, L.R. Brown, J. Mol. Spec. 251 (2008) 27

Experiment: FS-CRDS NIST Frequency Stabilized Cavity Ring-Down Spectrometer Serial Number: JONUMBA1 Joseph T. Hodges’ Lab Nanoscale and Optical Metrology Group Process Measurements Division Lowest detectable line intensity (S meas ): 2.5E-31 cm/molec TEM 00 Image

Experiment: Thermometry Our experiments probe transitions with relatively high lower state energies. Thus, thermometry can be an important uncertainty component. Measurement uncertainty = 15 mK Gradient uncertainty = 23 mK Combined uncertainty = 28 mK Thermometry error bars = 0.05 – 0.15% S.S. Penner, Quantitative Molecular Spectroscopy and Gas Emissivities (1959) +1 degree (297 K) -1 degree (295 K)

Experiment: Data Collection How we collected data: 1. Lock the cavity length (fix the FSR). 2. Detune probe laser from line center 1a. Specify scan length (GHz) 4. Jump the probe laser through one FSR 5. Find TEM 00 and collect ring-down signals 3. Find TEM 00 and collect ring-down signals Measured FSR = (12) MHz Reached end of scan? NO 6. Stop the current scan YES 1b. Specify signal to noise ratio At desired SNR? 7. Stop data collection YES NO

Results: Spectral Analysis Single spectrum of P P 41 (41) taken at approx. 296 K and 7 kPa of O 2 Average of 50 spectra of P P 51 (51) taken at approx. 296 K and 12.5 kPa of O 2 S meas = (30) E-28 cm/molec S meas = 1.10 (31) E-30 cm/molec SNR = 4:1 SNR = 180:1 Line profile: Galatry All parameters floated for J’ < 42 Narrowing parameter constrained for J’ > 40 L. Galatry, Phys. Rev. 122 (1961) 1218 P P 41 (41) P P 51 (51)

Results: Uncertainty Analysis Line Intensities Sources considered: Broadening Parameters Sources considered: Galatry Fit Uncertainty (Area) (“A”) (0.2% - 28%) Thermometry (“B”) (0.05% %) Pressure Measurement (“B”) (0.2%) FSR Measurement (“B”) (< 0.01%) Galatry Fit Uncertainty (Width) (“A”) (1% - 34%) Measurement Reproducibility (“A”) (0.1% - 6%) Measurement Reproducibility (“A”) (0.5% - 20%) Quadrature Sum As J’ increases the uncertainties in line parameters are dominated by contributions from etalons that are challenging to quantify. Reported Uncertainty: 0.3% to 29% Reported Uncertainty: 1% to 35% Quadrature Sum

Comparison to the Literature: Line Intensities S ref = HITRAN 2004 Our new measurements are in excellent agreement with previous A-band studies. We have extended the range of experimental data by about 30% in J’ and 40% in E rot.

Results: A Possible Herman-Wallis Effect S ref = HITRAN 2008 Changes to HITRAN 2008 vs. HITRAN 2004 lie only in the choice of band strength. The J- dependence was left unchanged. Our new results suggest the need for a subtle Herman-Wallis correction to the line intensities in the A-band. R. Schermaul and R.C.M. Learner, J. Quant. Spec. Rad. Trans. 61 (1999) 781 R. Herman and R.F. Wallis, J. Chem. Phys. 23 (1955) 637

Comparison to the Literature: Broadening Parameters L.R. Brown and C. Plymate, J. Mol. Spec. 199 (2000) 166 S.F. Yang, M.R. Canagaratna, S.K. Witonksy, S.L. Coy, J.I. Steinfeld, R.W. Field, A.A. Kachanov, J. Mol. Spec. 201 (2000) 188 D.J. Robichaud, J.T. Hodges, P. Masłowski, L.Y. Yeung, M. Okumura, C.E. Miller, L.R. Brown, J. Mol. Spec. 251 (2008) 27

Significance of the Experiments I. Extended O 2 A-band Data Range II. Exploited FS-CRDS for Spectroscopy of High-J States Intensities: High-J lines don’t saturate in the atmosphere. Quantitative intensities are useful. Broadening Parameters: Existing correlations with J’ were unproven. This is important in the atmosphere. Characterizing Highly Rotationally Excited Molecules: Important in experiments operating far away from room temperature (dynamics). CO 2 – Best case scenario we could push this to measure J = 126 in the infrared at room temperature.

Take Home Messages We measured line parameters for high-J transitions in the O 2 A-band at room temperature. Quantitative information on the line parameters up to J’ = 50 (E rot = 3780 cm -1 ) was extracted. This was done for pure O 2 and 20% O 2 in air. Frequency stabilization (FS-CRDS) was exploited to average over experimental spectra. An averaged spectrum was presented of a J’ = 50 line having S meas = 1E-30 cm/molecule. Changes to the O 2 A-band line parameters in HITRAN 2008 were driven by our previous experimental measurements. Here we extended the available range of data by an additional 30% in J’ and 40% in E rot and suggest the possibility of a subtle Herman-Wallis correction to the line intensities.

Acknowledgements My co-workers on this project Joseph T. Hodges – National Institute of Standards and Technology David A. Long – California Institute of Technology Charles E. Miller – Jet Propulsion Laboratory Mitchio Okumura – California Institute of Technology Herbert M. Pickett – Jet Propulsion Laboratory My bosses James R. Whetstone – Process Measurements Division Chief – National Institute of Standards and Technology Roger D. van Zee – Nanoscale and Optical Metrology Group Leader – National Institute of Standards and Technology Contributors to our previous O 2 A-band work David J. Robichaud – National Renewable Energy Lab Daniel Lisak – Uniwersyten Mikolaja Kopernika Piotr Masłowski – Uniwersyten Mikolaja Kopernika Laurence Y. Yeung – California Institute of Technology Linda R. Brown – Jet Propulsion Laboratory

Extra Slide: Branch Dependence S ref = HITRAN 2004 The bifurcation in our data beyond our stated error bars seems to be correlated with the branch of the transition. PQ and PP transitions diverge at higher J with respect to S ref.