Observations of D/H ratios in H2O, HCl, and HF on Venus and new DCl and DF line strengths☆

Abstract Intensities of the spectral lines in the fundamental bands of D 35 Cl and DF were calculated using the semi-empirical dipole moment functions derived from the most accurate and precise measurements of intensities of the ro-vibrational lines of H 35 Cl and HF. Values obtained in this way for the deuterated species are superior to any available measured or calculated data to date. Our study of the D/H ratios in H 2 O, HCl, and HF on Venus is based on spatially-resolved high-resolution spectroscopy using the CSHELL spectrograph at NASA IRTF. Search for DF on Venus using its R5 (1-0) line at 3024.054 cm −1 results in a DF mixing ratio of 0.23 ± 0.11 ppb that corresponds to (D/H) HF  = 420 ± 200 times that in the Standard Mean Ocean Water (SMOW). H 2 O abundances on Venus were retrieved using lines at 3022.366 and 3025.761 cm −1 that were observed at an exceptionally low overhead telluric water abundance of 0.3 pr. mm. The measured H 2 O mixing ratios at 74 km vary insignificantly between 55°S and 55°N with a mean value of 3.2 ppm. When compared with simultaneous observations of HDO near 2722 cm −1 , this results in (D/H) H2O  = 95 ± 15 times SMOW. Reanalysis of the observation of the D 35 Cl R4 (1-0) line at 2141.540 cm −1 (Krasnopolsky, V.A. [2012b]. Icarus 219, 244–249) using the improved line strength and more thorough averaging of the spectra gives (D/H) HCl  = 190 ± 50 times SMOW. The similarity of the measured (D/H) H2O  = 95 ± 15 at 74 km with 120 ± 40 observed by De Bergh et al. (De Bergh, C., Bezard, B., Owen, T., Crisp, D., Maillard, J.P., Lutz, B.L. [1991]. Science 251, 547–549) below the clouds favors the constant (D/H) H2O from the surface to the mesosphere, in accord with the prediction by theory. D/H ≈ 100 removes a difference of a factor of 2 between H 2 O abundances in the observations by Krasnopolsky (Krasnopolsky, V.A. [2010b]. Icarus 209, 314–322) and the Venus Express nadir observations (Cottini, V., Ignatiev, N.I., Piccioni, G., Drossart, P., Grassi, D., Markiewicz, W.J. [2012]. Icarus 217, 561–569). Equivalent widths of the HDO and H 2 O lines are similar in our observations; therefore some errors cancel out in their ratios. Photochemistry of HCl in the mesosphere tends to enrich D in HCl and deplete it in H 2 O. This may be an explanation of the twofold difference between the observed D/H in HCl and H 2 O. An alternative explanation is based on (D/H) H2O  ≈ 200 observed in the mesosphere by Bjoraker et al. (Bjoraker, G.L., Larson, H.P., Mumma, M.J., Timmermann, R., Montani, J.L. [1992]. Bull. Am. Astron. Soc. 24, 995) and Fedorova et al. (Fedorova, A. et al. J. Geophys. Res. 113, E00B22). This means an effective exchange of D between H 2 O and HCl and almost equal D/H in both species. However, this requires a twofold increase in D/H from the lower atmosphere to the mesosphere. This increase is not supported by theory; furthermore, condensation processes usually deplete D/H above the clouds. Photochemistry of HF has not been studied; it proceeds mostly in the lower thermosphere, and D/H in HF may be very different from that in H 2 O. Overall, the observational data on D/H in all hydrogen-bearing species on Venus are helpful to solve the problem of deuterium fractionation on Venus.

[1]  V. Krasnopolsky.  Spatially-resolved high-resolution spectroscopy of Venus 1. Variations of CO2, CO, HF, and HCl at the cloud tops , 2010 .

[2]  V. Krasnopolsky,et al.  A photochemical model for the Venus atmosphere at 47–112 km , 2011 .

[3]  M. Gurwell,et al.  SWAS observations of water vapor in the Venus mesosphere , 2007 .

[4]  P. A. Bonczyk.  Determination of Einstein-A and linewidth dependence on pressure for 3.4-μm DF spectra. I. Absorption measurements for pure DF , 1975 .

[5]  A. Vandaele,et al.  Composition of the Venus mesosphere measured by Solar Occultation at Infrared on board Venus Express , 2008 .

[6]  T. Owen,et al.  Deuterium on Venus: Observations From Earth , 1991, Science.

[7]  J. Luhmann,et al.  Venus and Mars: Atmospheres, Ionospheres, and Solar Wind Interactions: Luhmann/Venus and Mars: Atmospheres, Ionospheres, and Solar Wind Interactions , 1992 .

[8]  V. Krasnopolsky.  Spatially-resolved high-resolution spectroscopy of Venus 2. Variations of HDO, OCS, and SO2 at the cloud tops , 2010 .

[9]  Alan T. Tokunaga,et al.  CSHELL: a high spectral resolution 1-5-μm cryogenic echelle spectrograph for the IRTF , 1993, Defense, Security, and Sensing.

[10]  R. Hartle,et al.  Identification of deuterium ions in the ionosphere of Venus , 1983 .

[11]  P. Bernath,et al.  Direct fit of experimental ro-vibrational intensities to the dipole moment function: Application to HCl , 2011 .

[12]  Vasilii Ivanovich Moroz,et al.  STELLAR MAGNITUDE AND ALBEDO DATA OF VENUS , 2022, Venus.

[13]  F. Robert,et al.  Hydrogen isotope exchange reaction rates: Origin of water in the inner solar system , 1994 .

[14]  D. W. Strecker,et al.  Properties of the clouds of Venus, as inferred from airborne observations of its near-infrared reflectivity spectrum , 1978 .

[15]  Y. Yung,et al.  Modeling the distribution of H2O and HDO in the upper atmosphere of Venus , 2008 .

[16]  U. Fink,et al.  Water vapor in the atmosphere of Venus. , 1972 .

[17]  A. Treiman,et al.  Chemistry of atmosphere-surface interactions on Venus and Mars , 2013 .

[18]  Volker Ebert,et al.  Laser-based measurements of line strength, self- and pressure-broadening coefficients of the H35Cl R(3) absorption line in the first overtone region for pressures up to 1 MPa , 2010 .

[19]  V. A. Parshev,et al.  Chemical composition of Venus' troposphere and cloud layer based on Venera 11, Venera 12, and Pioneer-Venus measurements , 1980 .

[20]  T. Encrenaz,et al.  The Thermal Profile and Water Abundance in the Venus Mesosphere from H2O and HDO Millimeter Observations , 1995 .

[21]  Giuseppe Piccioni,et al.  Water vapor near the cloud tops of Venus from Venus Express/VIRTIS dayside data , 2012 .

[22]  Eric Villard,et al.  HDO and H2O vertical distributions and isotopic ratio in the Venus mesosphere by Solar Occultation at Infrared spectrometer on board Venus Express , 2008 .

[23]  G. E. Moore,et al.  Infrared Line and Band Strengths and Dipole Moment Function in HCl and DCl , 1957 .

[24]  V. I. Moroz,et al.  WATER VAPOUR IN THE MIDDLE ATMOSPHERE OF VENUS : AN IMPROVED TREATMENT OF THE VENERA 15 IR SPECTRA , 1999 .

[25]  V. Krasnopolsky.  High-resolution spectroscopy of Venus: Detection of OCS, upper limit to H2S, and latitudinal variations of CO and HF in the upper cloud layer , 2008 .

[26]  Peter F. Bernath,et al.  The ACE-FTS atlas of the infrared solar spectrum , 2010 .

[27]  B. Fegley,et al.  The Oxidation State of the Lower Atmosphere and Surface of Venus , 1997 .

[28]  V. Krasnopolsky,et al.  S3 and S4 abundances and improved chemical kinetic model for the lower atmosphere of Venus , 2013 .

[29]  A. Vandaele,et al.  CO2 pressure broadening and shift coefficients for the 1–0 band of HCl and DCl , 2012 .

[30]  R. Clancy,et al.  Observations of HCl altitude dependence and temporal variation in the 70–100 km mesosphere of Venus , 2012 .

[31]  V. Krasnopolsky,et al.  Long-term spectroscopic observations of Mars using IRTF/CSHELL: Mapping of O2 dayglow, CO, and search for CH4 , 2007 .

[32]  Alan Fried,et al.  Spectral intensities in the fundamental bands of HF and HCl , 1985 .

[33]  Gordon L. Bjoraker,et al.  High‐resolution spectroscopy of Mars at 3.7 and 8 μm: A sensitive search for H2O2, H2CO, HCl, and CH4, and detection of HDO , 1997 .

[34]  Gang Li,et al.  The HITRAN 2008 molecular spectroscopic database , 2005 .

[35]  P. Bernath,et al.  Reference spectroscopic data for hydrogen halides. Part I: Construction and validation of the ro-vibrational dipole moment functions , 2013 .

[36]  Anna Fedorova,et al.  The 1.10- and 1.18-μm nightside windows of Venus observed by SPICAV-IR aboard Venus Express , 2011 .

[37]  Y. Yung,et al.  Absorption Cross Sections of HCl and DCl at 135-232 Nanometers: Implications for Photodissociation on Venus , 2001 .

[38]  David Crisp,et al.  Near-infrared light from Venus' nightside - A spectroscopic analysis , 1993 .

[39]  C. Piccolo,et al.  Pressure broadening and shift of transitions of the first overtone of HCl , 2001 .

[40]  L. Wallace,et al.  An atlas of the solar spectrum in the infrared from 1850 to 9000 cm-1 (1.1 to 5.4 μm), revised , 2003 .

[41]  A. Watson,et al.  Venus Was Wet: A Measurement of the Ratio of Deuterium to Hydrogen , 1982, Science.

[42]  V. Krasnopolsky,et al.  Oxygen and carbon isotope ratios in the martian atmosphere , 2007 .

[43]  V. Krasnopolsky.  Observation of DCl and upper limit to NH3 on Venus , 2012 .

[44]  R. H. Hunt,et al.  Line strengths, line widths, and dipole moment function for HCl , 1970 .

[45]  J. Lamouroux,et al.  Half-widths, their temperature dependence, and line shifts for the HDO–CO2 collision system for applications to CO2-rich planetary atmospheres , 2011 .