Line-shapes and intensities of carbon monoxide transitions in the (3 0) band

1. Line-shapes and intensities of carbon monoxide transitions in the (3 0) band Z. Reed,*O. Polyansky,†J. Hodges* * National Institute of Standards and Technology †University College of London

2. Carbon monoxide Line Shapes and Intensities • Carbon monoxide is present in the planetary atmospheres of most planets in this solar system and is a useful probe of atmospheric dynamics • CO is an excellent test case for lineshape modeling • CO can readily be modeled theoretically, presenting a possible approach to link optical measurements to the SI without the use of artifact gas standards

3. Previous Work • Extensive study has been performed on self-, nitrogen-, and air-broadened CO in the , , and bands [1] • Intensities of the band have been previously determined [1-3] • Systematic variation from the Voight profile has been revealed, along with deviations from HITRAN2012 line intensities and a dependence on chosen line shape model [1] Mondelain, D., et al., Broadband and highly sensitive comb-assisted cavity ring down spectroscopy of CO near 1.57 μm with sub-MHz frequency accuracy. Journal of Quantitative Spectroscopy and Radiative Transfer, 2015. 154: p. 35-43 [2] Wójtewicz, S., et al., Low pressure line-shape study of self-broadened CO transitions in the (3←0) band. Journal of Quantitative Spectroscopy and Radiative Transfer, 2013. 130: p. 191-200. [3] Henningsen, J., et al., The 0 → 3 Overtone Band of CO: Precise Linestrengths and Broadening Parameters. Journal of Molecular Spectroscopy, 1999. 193(2): p. 354-362.

4. optical resonator pzt cw probe laser decay signal frequency - stabilized time (a) reference laser cavity stabilization servo stabilized comb of absorption spectrum resonant frequencies n = 108 MHz FSR (b) frequency • Frequency Stabilized Cavity Ringdown Spectroscopy (FS-CRDS) at NIST Gaithersburg I = I0exp-(t/t) + const frequency time 1/(c t) = a0 + a(n) Hodges, J.T., et al, Rev. Sci. Instrum., 2005, 76, 2

5. Linking measured line parameters to the SI Cs Clock Cavity length servo Optical FrequencyComb Gas-filled, length-stabilizedring-down cavity I2-stabilized HeNe laser (10 kHz) Probe Laser frequency time Probe laser servo CalibratedThermometers (PRT) CalibratedManometers (SRT) 1/(c t) = a0 + a(n) Primary Temperature Standards Primary PressureStandards

6. S = ∫a(n)dn/{ n∫g(n)dn} = A/n fitted spectrum area measured absorption coefficient line profile (unity area) Measurement of Line Intensity (S) and Absorber Concentration (n) Once the intrinsic property S is known, then n = A/S

7. Hartmann-Tran Line Profile • Includes mechanisms for collisional narrowing, speed dependent narrowing and shifting, and correlation between velocity- and phase- changing collisions

8. HTP Profile reduces to: Voight profile (VP) when , , , η = 0 Nelkin-Ghatak (NGP) when , , η = 0 Speed-dependent VP when , η = 0 Quadratic speed dependent NGP when , η= 0 Where = absorber mass mass diffusion coefficient Complex profile Complex, normalized narrowing frequency Quadratic approximation to speed dependence Mechanisms: 1) collisional narrowing (hard-collision model), 2) speed-dependent broadening and shifting, 3) partial correlations between velocity-changing and dephasing collisions

9. Line Profiles Measured and fit results of the N2-broadened 13CO transition P3, measured at a total pressure of 13.33 kPa and 296K Upper panel, measured (symbols) and fit (line) absorption spectrum Lower panes show fit residuals and QF values for individual profiles

10. Line Profiles Line Mixing α(ν)=A{Re I (ν- ν0) + Y Im(I (ν- ν0)) } Where A = fitted area Y= dimensionless line mixing term Re(I) = real component Im (I)= imaginary component Measured and fit results of the N2-broadened 13CO transition P3, measured at a total pressure of 13.33 kPa and 296K Upper panel, measured (symbols) and fit (line) absorption spectrum Lower panes show fit residuals and QF values for individual profiles

11. Fitted Area Dependence Relative fitted area of N2-broadened 13CO transition P3 measured at a total pressure of 13.33 kPa and 296K, as a function of varying line profiles. Voight profile systematically underestimates line area

12. Line Intensity Determination n must be known to determine S NIST CO in N2 standard prepared via gravimetric weighing method 11.9858%±0.00095 CO in N2 Once the intrinsic property S is known, then n = A/S

13. Line Intensity Determination Linear fit of fitted line areas of N2-broadened 13CO transition P3 measured at 296K at pressures ranging from 50 torr to 350 torr. Spectra are fitted with SDNGP profile with line mixing.

14. Measurement repeatability Normalized line strengths determined via repeated experiment (symbols). Error bar represent individual fit uncertainty Calculated line strengths and combined uncertainty

15. Comparison to Literature and Theory All electron MRCI calculations with highest available basis set in MOLPRO Aug-cc-pCV6Z results are extrapolated to complete basis set limit First and second order relativistic corrections and adiabatic corrections included [1] Wójtewicz, S., et al., Low pressure line-shape study of self-broadened CO transitions in the (3←0) band. JQSRT, 2013. 130: p. 191-200. [2] A. A. Kyuberis, L. Lodi, V. Ebert, N. F. Zobov, J. Tennyson, O. L. Polyansky

16. Error Budget

17. Conclusions • Line strengths of selected 12C16O, 13C16O, and 12C18O transitions in the (3 0) band measured at highest precision to date • Calculated line strengths vary significantly from HITRAN and previous literature values, but compare well to ab initio calculations • Link to SI and theoretical line strengths demonstrates possible route to artifact-free determination of molecular concentrations, including isotope ratios Funding: NIST Greenhouse Gas Measurements and Climate Research Program