The importance of being earnest about line shapes!!

1. The importance of being earnest about line shapes!! Charles E. Miller and Linda R. Brown Jet Propulsion Laboratory, California Institute of Technology 4800 Oak Grove Dr., Pasadena, California 91109 Acknowledgments The research at the Jet Propulsion Laboratory (JPL), California Institute of Technology, was performed under contract with National Aeronautics and Space Administration.

2. Return global XCO2 data with 0.3% precision Our Research Goal: Improve CO2 and O2 line parameters

3. Better Accuracies Require Precise Knowledge/Control of the Experimental State • Pristine cells – no contamination • Temperature monitoring inside the cell • Isotopic enriched samples • Mass spectrometric standard samples • Stable spectrometer performance Four Temp Probes (PRT) going Inside the Cell Goal for Experimental Uncertainties: Abundances:0.05% (purity, Isotope) Pressure:0.01 Torr (if P > 10 Torr) Temperature:0.1 K Path:2 mm (0.1%) Signal/noise: 2000:1 Resolution: nearly Doppler-limited 100% Trans:  0.1% 0% Trans:  0.1% Instrumental line shape

4. Molecular Line Shape Problem! Miller et al. Comptes Rendus Physique 6 (2005). Voigt only Strange residuals (!) non-Voigt line shapes (line mixing + speed dependence + narrowing) Multispectrum retrievals one solution for all lines fitting all spectra simultaneously [modified from Benner et al. JQSRT 53, 705 (1995)] NEW CO2 Lab parameters could not be used in (Voigt only) atmospheric retrievals.

5. Too many line shape choices! Lisak et al. 2010 O2 B-band

6. What we have to do now! • Learn what combination of line shapes can produce the best atmospheric retrievals. • Create and Validate universal software using the required molecular shapes to compute synthetic spectra (radiances etc….). • Give standardized software to both atmospheric and lab spectroscopists: So that new lab parameters will be consistent with atmospheric calculations.

7. Need to do better lab studies Conventional Strategy: Sequential L-B-L analyses Quantum modelingPres. (atm) 1st Positions: < 0.001 2nd Intensities: < ~ 0.010 ToCreate good database for broadening retrievals 3rd Shapes: Lorentz: 0.10 – 1. Narrowing & 0.03 – 0.1 Speed Dependence (Lorentz=Doppler) Line mixing: 0.5 – 10 Collision Induced Abs: 1 – 20 ? • Use community-validatedmulti-spectrum retrieval codes that permit us to obtain consistent values of line shape parameters. (do intercomparisons) • Usegas pressure that can revealallactivated line shapes(Voigt, speed dependence, line mixing, narrowing …..). • Excellent instrumental performance (usual stuff).

8. STRATEGY: Fit all lines and spectra simultaneously BUT Constrainpositions and intensities and adjust constantsin the quantum mechanical equations (instead of fitting line-by-line) Pressure broadening parameters still fitted line-by-line Constraining multispectrum fits! Line Positions: νi = ν0 + B(J(J+1)) - D(J(J+1))2 + H(J(J+1))3 – E" ν i Resonant frequency ν 0 Band origin J Rotational quantum number E" Lower state rotational energy (fixed) ν0, B, D, H, upper state constants of each band in the region, are the adjusted instead of individual positions. Line Intensities: Si = (ni/n0)(Sv/Li) exp(-hcEi″/kT)[1-exp(hcvi/kT)]F Si, observed individual line intensity Sv vibrational band intensity, F Herman-Wallis factor = [1+A1m+A2m2+A3m3]2 Li Hönl-London factor, where li= (m2-l″2)/|m| for CO2 m = J″+1 R branch, m = -J″ for the P branch J″, l lower-state rotational & angular momentum quanta Qr lower state rotational partition function at T0=296 K Ei″ lower state rotational energy Sv,A1,A2are the adjusted parameters Can we do this for asymmetric tops? symmetric tops?

9. Fits to laboratory and atmospheric spectra must use the same line shape formulations Create new universal line shape (LS) software Validate LS formulations Expand databases to include all necessary LS parameters Convince sponsors to fund it! CALL TO ACTION! Coming goal:0.1% accuracy for strongest bands