SELF- AND CO 2 -BROADENED LINE SHAPE PARAMETERS FOR THE 2 AND 3 BANDS OF HDO V. MALATHY DEVI, D. CHRIS BENNER, Department of Physics, College of William and Mary, Williamsburg, VA. K. SUNG, L.R. BROWN, Jet Propulsion Laboratory, California Institute of Technology, Pasadena, CA. A.W. MANTZ, Department of Physics, Astronomy and Geophysics, Connecticut College, New London, CT. M.A.H. SMITH, Science Directorate, NASA Langley Research Center, Hampton, VA. R.R. GAMACHE, Department of Environmental, Earth, and Atmospheric Sciences, University of Massachusetts, Lowell, MA. G.L. VILLANUEVA, Astrochemistry, NASA Goddard Space Flight Center, Greenbelt, MD. ACKNOWLEDGMENTS The research performed at the College of William and Mary was supported by a Grant from NASA’s Mars Fundamental Research Program (NNX13AG66G ). The research at Jet propulsion Laboratory, California Institute of Technology, Connecticut College and NASA Langley Research Center was conducted under contracts and cooperative agreements with the National Aeronautics and Space Administration. 70 th INTERNATIONAL SYMPOSIUM ON MOLECULAR SPECTROSCOPY University of Illinois, Champaign-Urbana, June 22-26, 2015

1.Introduction 2.Sample preparation 3.Sample spectra (laboratory observed) 4.Spectral regions needed for Planetary studies 5.Equations used in the analyses 6.“Preliminary” Results (graphical) (a) 2 band (b) 3 band 8. Preliminary results (Tabular form) 9. Summary and work to be done OVERVIEW OF THE PRESENTATION

Lack of knowledge of accurate HDO-CO 2 widths and their temperature dependences is an ongoing concern for astronomers interpreting Mar’s data and to determine reliable D/H. Combined measurements of HDO and H 2 O abundances are the only feasible means to obtain Mar’s atmospheric D/H. Room temperature measurements of CO 2 broadened widths for H 2 O in 2 and rotational bands are available, but none for HDO in any band even at room temperature. Significant systematic inaccuracies in the knowledge of the widths and their temperature dependences can adversely affect the retrievals of D/H. At present, only unconfirmed theoretical predictions of broadening coefficients are available, impacting the predictions of the H 2 O and HDO retrievals and hence D/H. Temperature dependences of CO 2 -broadened HDO line widths are critical since the uncertainty in the temperature dependence of half-widths leads to large errors in the retrieved mixing ratios and hence in column abundances. Why Are These Measurements Important?

Pure HDO does not exist in nature due to isotopologue exchange reaction. HDO samples, prepared by mixing high purity distilled H 2 O and 99% pure D 2 O 50%-50% mixtures of H 2 O and D 2 O were used giving H 2 O(50%)+D 2 O(50%) → H 2 O(25%)+HDO(50%)+D 2 O(25%) HDO BandBand strength (cm -2 atm -1 at 296 K Spectral regionExpected application 1 A type: 53.2 B type: cm -1 (3.67  m) NIRSPEC/Keck-II, TEXES 2 A type: B type: cm -1 (7.13  m) Express, OMEGA, PFS on board the Mars 3 A type: B type: cm -1 (2.70  m) Express satellite SOIR. MAVEN mission, MSL etc. A Type (parallel), B Type (perpendicular) or a mixture of both (hybrid). 1, 2 and 3 band centers of H 2 O are: 3657 cm -1 (2.73  m), 1595 cm -1 (6.26  m), 3756 cm -1 (2.66  m), respectively.

NIRSPECC at Keck-II (Villanueva et al. 2012). HDO lines near 2722 cm -1 ( 1 ) HDO in the 3 band. MSL selected site (Webster and Mahaffy 2011) Laboratory spectra: (a) HDO; (b) HDO+CO 2   

EXPERIMENTAL AND DATA RETRIEVALS Spectra were recorded using the Bruker 125HR FTS at JPL. A cm path coolable cell designed and built at Connecticut College by Prof. Arlan Mantz contained the gas samples. Sample temperatures range from 255 to 296 K. A few additional spectra at lower temperatures are planned. The spectral resolutions were between and 0.01 cm  1. Pressures for HDO mixtures were in the 0.55  14.3 Torr range Total pressures of HDO mixtures and CO 2 varied between 39 and 317 Torr. The Volume Mixing ratios of HDO were ~  lines of H 2 O and the 3 lines of CO 2, as appropriate, were used for wavenumber calibration. DATA ANALYSIS All spectra obtained for each band were fitted simultaneously using the multispectrum fitting software developed by Dr. D. Chris Benner (W&M). Isotopologue abundances in each spectrum were determined from least squares fittings.

P = 9.56 Torr T = K L = cm P = 6.94 Torr T = K L = cm P = 9.86 Torr T = K L = cm SAMPLE SPECTRA OF MIXTURES OF H 2 O+HDO+D 2 O

Equations used in retrieving the line shape parameters (1) (2) (3)

Example of a multispectrum fit of HDO 2 lines near 1347 cm  1 The three strong lines and the weak line seen in this fitted interval are all HDO. 1)  at (6) cm  1 2)  at (6) cm  1 3)  at (6) cm  1 The weak line at (3) cm  1 is 

Examples of line mixing (via off-diagonal relaxation matrix) for HDO-CO 2 and HDO-HDO measured in the 1 and 2 bands of HDO  1  2

A SAMPLE LIST OF MEASURED PARAMETERS

Line parameters including the measured Off-Diagonal Relaxation Matrix Element Coefficients: A few examples

Line position differences (Measured – Prediction) and Line Intensities (Measured and Prediction) in the v 2 and v 3 bands Top: Position differences for the majority of lines are within ± cm -1. Weaker lines show larger differences. Bottom: The measured intensities for some of the stronger lines are larger than predicted values. Top: Position differences for the majority of lines are within ± cm -1. Bottom: The measured intensities are close to predicted values.

HDO-CO 2 and HDO-HDO halfwidth coefficients in 2 & 3 : Measurements and Predictions (R. Gamache) Measured and predicted half-width coefficients for HDO-CO 2 and HDO-HDO (top and bottom panels) for 2 plotted vs. K m + 0.1*(J m - K m ). Measured and predicted half-width coefficients for HDO-CO 2 and HDO-HDO (top and bottom panels) for 3 plotted vs. K m + 0.1*(J m - K m ).

Temperature dependence exponents for HDO-CO 2 half-width coefficients and pressure-shift coefficients in 2 and 3 : Measurements and Predictions Top: The measured temperature dependence exponents are larger than predicted values. Bottom: Measured HDO-CO 2 pressure-shift coefficients are larger than measured values. Top: Generally, the measured temperature dependence exponents are comparable to predicted values. Bottom: There are no HDO-CO 2 pressure-shift coefficients (yet) predicted for this band.

Temperature dependence for HDO-CO 2 pressure shift coefficients: Measurements Temperature dependence of HDO-CO 2 pressure-shift coefficients for 2 are both positive and negative and varies in the & cm -1 atm -1 K -1 range. Temperature dependence for 3 band HDO-CO 2 pressure-shift coefficients varies between 0 and cm -1 atm -1 K -1.

CONCLUSIONS AND FUTURE PLANS Line positions, intensities, and CO 2 -broadened halfwidth and pressure-shift coefficients, and their variations with temperature have been measured for several transitions in the 2 and 3 bands of HDO. Room temperature self-broadened halfwidth coefficients and pressure-shift coefficients are measured for transitions in both bands; but the number of measurements are much fewer than for HDO-CO 2. Line mixing using the off-diagonal relaxation matrix formalism was quantified for HDO-HDO and HDO-CO 2 mixing in several transition pairs in 2 & 3. Temperature dependences of HDO-CO 2 pressure-shift coefficients are also determined for several transitions in 2 and 3. FUTURE PLANS INCLUDE 1. Additional data at lower sample temperatures are planned for all three bands, especially for the Theoretical modeling of measured parameters using the CRB formalism will be performed (R.R. Gamache).

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