Self- and air-broadened line shape parameters in the band of 12 CH 4 : cm -1 V. Malathy Devi Department of Physics The College of William and Mary Williamsburg, Virginia International Symposium on Molecular Spectroscopy 69th Meeting - June 16-20, Champaign-Urbana, Illinois ACKNOWLEDGMENT The research performed at the College of William and Mary, Connecticut College and NASA Langley Research Center was supported by NASA’s ASCENDS program. Part of the research conducted at the Jet Propulsion Laboratory was performed under contract with National Aeronautics and Space Administration. A. Predoi-Cross was funded by the Natural Sciences and Engineering Research Council of Canada.

D. Chris Benner Department of Physics, The College of William and Mary, Williamsburg, Virginia, USA Mary Ann H. Smith Science Directorate, NASA Langley Research center, Hampton, VA, USA Arlan W. Mantz Department of Physics, Astronomy and geophysics, Connecticut College, Connecticut, USA Keeyoon Sung, Linda R. Brown, Timothy J. Crawford Jet Propulsion Laboratory, California Institute of Technology, Pasadena, California,USA Adriana Predoi-Cross Department of Physics and Astronomy, The University of Lethbridge, 4401 University Drive, Lethbridge, Alberta, Canada co-authors are:

1.Objective 2.Prior studies of the band investigated in this work 3.Experimental details 4.Sample Spectra 5.Instrumental line shape effects 6.Analysis technique 7.Sample multispectrum fits 8.Results 9. Off-diagonal Relaxation Matrix Element Coefficients 10. Summary and Future plans The following topics will be briefly discussed

Objectives The methane band system in the 2.3-  m region ( Octad ) is of interest not only for measurements of CH 4 atmospheric profiles, but also because it overlaps the spectra of other atmospheric molecules such as CO and HF The level of accuracy for line shape parameters in the Octad region of both 12 CH 4 and 12 CH 4 is less compared to those for the lower polyads, Dyad and Pentad Information on line shapes for bands in this spectral region do not meet the desired accuracy requirements to support remote sensing applications such as ASCENDS (Active Sensing of CO 2 Emissions over Nights, Days and Seasons) retrievals One of the major goals of this study was to measure the temperature dependences of Lorentz self- and air-broadened halfwidth, pressure-shift and line mixing (off-diagonal relaxation matrix elements) coefficients for transitions in the band of 12 CH 4 A multispectrum fitting technique to include speed dependent Voigt profile and full line mixing is applied to fit several spectra (room and cold) simultaneously

Prior line shape studies include the following: Multispectrum analysis of 12 CH 4 in the cm -1 (room temperature air-broadening) A. Predoi-Cross et al. J. Mol. Spectrosc 236 (2006) Multispectrum analysis of 12 CH 4 in the cm -1 (room temperature self-broadening) A. Predoi-Cross et al. J. Mol. Spectrosc 232 (2005) Line mixing effects in the band (room temperature air-broadening). A. Predoi-Cross et al. J. Mol. Spectrosc. 246 (2007) Air-broadening and pressure shifts in the 2.3  m region (room temperature air-broadening) V. Malathy Devi et al. J. Mol. Spectrosc 157 (1993) Temperature dependences of Lorentz air-broadening and pressure shifts in the 2.3  m region. V. Malathy Devi et al. J. Quant Spectrosc Radiat Transfer 51 (1994) Other research groups are investigating N 2 -broadened line shape parameters for the Octad bands

Experimental setup and gas conditions Configuration and conditions JPL Bruker IFS 125HR FTS Spectrum Band pass (cm -1 ) Light SourceGlobar Beam SplitterCaF2 DetectorInSb Resolution (cm -1 ) (unapodized)0.005 Maximum Optical Path Difference (cm)100 Focal length of the collimating lens (mm)418 Source aperture diameter (mm)1.0 Sample pressure Pure CH 4 (Torr) Total sample pressure (Torr) for CH 4 +air Volume mixing ratio of CH 4 in air-broadened spectra Gas sample temperature (K) Absorption Path length (cm)20.38 Cell windowsZnSe Vacuum box windowsKBr (wedged) Scanning time (h)3-4 Signal-to-noise~ Calibration standards usedH 2 O a, CO b,CH 4 b a Relative calibration of wavenumber scales with respect to 3 H 2 O lines [HITRAN12] b Absolute calibration with respect to CH 4 lines [Predoi-Cross et al. J. Mol. Spectrosc. 232 (2005) ]

Summary of Experimental Conditions of Spectra Analyzed Spectrum #Gas sample Volume mixing ratio Pressure (Torr) T (K)Calibration CH CH CH CH CH CH CH CH CH 4 +air CH 4 +air CH 4 +air CH 4 +air CH 4 +air CH 4 +air Torr = 1 atm = kPa = bar The 12 CH 4 sample was 99.95% enriched in 12 C Additional spectra for background and calibration were recorded but not listed here

Three of the 14 spectra analyzed in this study Cell path length = cm (a) Self-broadened 12 CH 4 spectrum with 385 Torr at K (b) Self-broadened 12 CH 4 spectrum with 169 Torr at 200 K (c) 12 CH 4 +air with 225 Torr total pressure and methane volume mixing ratio of 0.04

Equations used to retrieve: Lorentz self- and air-broadened widths, shifts and their temperature variations

Multispectrum fit of the P(4) manifold in Path length = cm (a) Weighted (obs- calc) fit residuals (b) Multispectrum fit of 14 spectra on an expanded ( ) vertical scale (c) Same as in the above panel (b), but on a (0-1) vertical scale The short vertical lines are positions of transitions included in the fit

Multispectrum fit of the R(6) manifold in (a) Weighted (obs-calc) fit residuals; Voigt with speed dependence (b) Weighted (obs-calc) fit residuals; Voigt, with speed dependence and full line mixing (c) Multispectrum fit (on an expanded vertical scale: top 10%) (d) Same as in panel (c), plotted on a vertical scale The short vertical lines are positions of transitions included in the fit

Multispectrum fit of the “allowed” Q branch transitions in the band (a) Weighted (obs-calc) fit residuals with speed dependence and full line mixing (b) Weighted (obs-calc) fit residuals using the HITRAN12 line parameters (c) Final fit of all 14 experimental spectra The short vertical lines are positions of transitions included in the fit

Comparisons of line positions and Ratios of line Intensities Line intensities and Lorentz width and shift coefficients

Comparisons of self- and air- widths and pressure-shifts coefficients Comparisons of temperature dependences of widths and pressure-shifts Coefficients

Sample of measured line parameters J′ C′ n′ a J″ C″n″ b Position(cm -1 )ScSc % err % err  ′ g ×10 5 SD h × F1 444 F ( 3) (3) i i 631 j (7) -8.32(12) -11.5(3) -8.8(3) 8.13(6) 3.49(11) 69(1) 3 E 294 E (4) (3) (12) i 586 j 603 k (8) -8.65(24) -11.9(5) -10.4(4) (33) 10.55(8) 5.91(22) -1.35(55) 69(2) 3 F2 424 F (3) (3) (10) i 657 j 673 k (8) -8.36(13) -11.7(4) -10.3(4) (32) 9.63(8) 4.59(13) -2.12(53) 54(1)

Sample of measured off-diagonal relaxation matrix element coefficients Line mixing pair (s) Line ID Line position (cm -1 ) Off-diagonal relaxation matrix element coefficients (in cm -1 atm -1 at 296 K) Self- broadening Air- broadening T-dep. (self-mixing) T-dep. (air-mixing) P(4) F 3F1 44←4F2 1 3F2 42←4F (9) (5) a (8) e (29) (3) a (6) e f 0.8(F) 0.8(F) e f P(3) F 2F1 30←3F2 1 2F2 32←3F (12) (3) a (37) (1) a f 0.82(4) 0.88(15) f R(6)A 7A2 33←6A1 1 7A1 31←6A (34) (11) a (1) b (1) d (8) e (79) (5) a (0) c (2) d (4) e f 0.8(F) 0.960(8) e 0.8(F) 1.063(6) e f R(6)F 7F2 94←6F1 1 7F1 96←6F (13) (4) a (1) b (1) d (F) e (25) (2) a (0) c (1) d (F) e f 0.8(F) 0.8(F) e 0.8(F) 0.8(F) e f a Predoi-Cross et al. ( ) J. Mol. Spectrosc. 246 (2007) b Smith et al. ( 4 ) self-broad. J. Quant. Spectrosc. Radiat Transfer 111 (2010) c Smith et al. ( 4 ) air-broad. J. Quant. Spectrosc. Radiat Transfer 110 (2009) d Smith et al. ( 2 ) self- and air- broad. J. Quant. Spectrosc. Radiat Transfer 153 (2014) e Devi et al. (2 3 ) Self- and air-broad. (Ongoing analysis) f HaTran (2 3 ) air-broad. Predicted values (Private communication)

SUMMARY:I 14 spectra (self- and air-broadened) recorded between K were fitted simultaneously to retrieve widths, shifts, relaxation matrix elements and speed dependence by employing a non-Voigt line shape model Off-diagonal relaxation matrix elements were measured for 10 pairs of line-mixed transitions The mean ratio and standard deviation of the Lorentz self- to air-widths coefficients =1.29(8) For the 22 comparisons made for the strong CH 4 line positions, HITRAN12 values are lower by (3) cm -1 compared to HITRAN08 Comparisons of positions in HITRAN08 with our earlier study [Predoi-Cross et al. JMS 232 (2005) ] agree within (8) cm -1 Present measurements agree with HITRAN08 values within (2) cm -1 and (1) cm -1 with our earlier study Self/airPositionIntensity Lorentz Width Pressure- shift n (width)δ′ (shift) Speed dependence self air

SUMMARY (cont.) First measurements of temperature dependence exponents for self-broadening and a combined analysis of both self- and air-broadened spectra for the  transitions Line positions, absolute line intensities, Lorentz self- and air-broadened widths, shifts, line mixing coefficients as well as their temperature dependences are determined Speed dependence parameter was determined for several transitions In most cases, temperature dependence exponents for air-broadened width coefficients were slightly larger compared to self-broadened width coefficients for same transitions Overall, for a given transition, temperature dependence for self-shift coefficient was larger compared to that for air-shift coefficient Even with data taken in the 150 K-298 K range, temperature dependence exponents of line mixing was determinable only for a few cases Future plans include similar analyses in the cm -1 region where the stronger Octad bands and occur

THANK YOU