Erratum: ``Vertical distribution of Titan's atmospheric neutral constituents''

The vertical distribution of Titan's neutral atmosphere compounds is calculated from a new photochemical model extending from 40 to 1432 km. This model makes use of many updated reaction rates, and of the new scheme for methane photolysis proposed by Mordaunt et al. [1993]. The model also includes a realistic treatment of the dissociation of N 2 , of the deposition of water in the atmosphere from meteoritic ablation, and of condensation processes. The sensitivity of the results to the eddy diffusion coefficient profile is investigated. Fitting the methane thermospheric profile and the stratospheric abundance of the major hydrocarbons requires a methane stratospheric mixing ratio of 1.5-2% rather than 3%. Fitting the HCN stratospheric profile requires an eddy diffusion coefficient at 100-300 km that is 5-20 times larger than that necessary for the hydrocarbons. Most species are reasonably well reproduced, with the exception of CH 3 C 2 H and HC 3 N. The formation of CH 3 CN may involve the reaction of CN with either CH 4 or (preferably) C 2 H 6 . The observed CO 2 profile can be modeled by assuming an external source of water of ∼6 × 10 6 cm -2 s -1 . For a nominal CO mixing ratio of 5 × 10 -5 , the chemical loss of CO exceeds its production by ∼15%, and equilibrium is achieved for CO = 1 × 10 -5 .

[1]  B. Bézard,et al.  First Ground-based Detection of Cyanoacetylene on Titan , 1992 .

[2]  G. Rottman,et al.  The solar absolute spectral irradiance 1150-3173 A - May 17, 1982 , 1983 .

[3]  Y. Yung,et al.  An update of nitrile photochemistry on Titan. , 1987, Icarus.

[4]  JOHN S. Lewis.  Satellites of the Outer Planets: Their Physical and Chemical Nature , 1971 .

[5]  M. Ashfold,et al.  Primary product channels in the photodissociation of methane at 121.6 nm , 1993 .

[6]  Christopher P. McKay,et al.  Elemental composition, solubility, and optical properties of Titan's organic haze , 1996 .

[7]  Paul N. Romani,et al.  Methane photochemistry on Neptune : ethane and acetylene mixing ratios and haze production , 1993 .

[8]  G. Marston,et al.  Branching ratios in the N + CH3 reaction - Formation of the methylene amidogen (H2CN) radical , 1989 .

[9]  Michael J. Berry,et al.  CN photodissociation and predissociation chemical lasers: Molecular electronic and vibrational laser emissions , 1974 .

[10]  M. Podolak,et al.  A numerical study of aerosol growth in Titan's atmosphere , 1980 .

[11]  T. Encrenaz,et al.  Modeling Titan's Thermal Infrared Spectrum for High-Resolution Space Observations , 1993 .

[12]  R. Samuelson,et al.  C3H8 and C3H4 in Titan's atmosphere , 1981, Nature.

[13]  B. Bézard,et al.  Hydrocarbons in Neptune's stratosphere from Voyager infrared observations , 1991 .

[14]  D. Shemansky,et al.  CO2 Extinction Coefficient 1700–3000 Å , 1972 .

[15]  D. L. Mcfadden,et al.  Gas-phase atom-radical kinetics of atomic hydrogen, nitrogen, and oxygen reactions with fluoromethylene radicals , 1990 .

[16]  D. W. Clarke,et al.  Photodissociation of cyanoacetylene: application to the atmospheric chemistry of Titan. , 1995, Icarus.

[17]  L. C. Lee.  CN(A 2Πi→X 2Σ+) and CN(B 2Σ+→X 2Σ+) yields from HCN photodissociation , 1980 .

[18]  T. Nakayama,et al.  Absorption and Photoionization Coefficients of Acetylene, Propyne, and 1‐Butyne , 1964 .

[19]  G. Marston,et al.  Measurement of the photoionization spectra and ionization thresholds of the H sub 2 CN and D sub 2 CN radicals , 1991 .

[20]  D. Gautier,et al.  Titan's thermal emission spectrum: Reanalysis of the Voyager infrared measurements. , 1995 .

[21]  M. C. Lin,et al.  CN radical reactions with selected olefins in the temperature range of 174-740 K , 1992 .

[22]  T. Owen,et al.  Millimeter and Submillimeter Heterodyne Observations of Titan: Retrieval of the Vertical Profile of HCN and the12C/13C Ratio , 1997 .

[23]  E. Lellouch,et al.  Titan's hypothesized ocean properties: The influence of surface temperature and atmospheric composition uncertainties , 1989 .

[24]  M. Allen,et al.  Titan: Aerosol photochemistry and variations related to the sunspot cycle , 1980 .

[25]  A. Coustenis,et al.  Titan's atmosphere from voyager infrared observations: III. Vertical distributions of hydrocarbons and nitriles near Titan's North Pole , 1991 .

[26]  S. Atreya,et al.  Evolution of a Nitrogen Atmosphere on Titan , 1978, Science.

[27]  L. Capone,et al.  Galactic cosmic rays and N2 dissociation on Titan , 1983 .

[28]  E. Koch,et al.  OPTICAL ABSORPTION OF GASEOUS METHANE, ETHANE, PROPANE, AND BUTANE, AND REFLECTION OF SOLID METHANE AND ETHANE IN THE VACUUM ULTRAVIOLET. , 1971 .

[29]  P. Monks,et al.  The kinetics of the formation of nitrile compounds in the atmospheres of Titan and Neptune , 1993 .

[30]  D. Strobel,et al.  Hydrocarbon photochemistry and Lyman alpha albedo of Jupiter , 1980 .

[31]  E. Lellouch,et al.  Titan's atmosphere and hypothesized ocean: A reanalysis of the Voyager 1 radio-occultation and IRIS 7.7-μm data , 1989 .

[32]  M. Nicolet.  Photodissociation of molecular oxygen in the terrestrial atmosphere: Simplified numerical relations for the spectral range of the Schumann‐Runge bands , 1984 .

[33]  L. Pasternack,et al.  Absolute rate constants for the reaction of cyanogen with methane, ethane, and propane from 292 to 1500 K using high-temperature photochemistry and diode laser absorption , 1991 .

[34]  R. Turco,et al.  A physical model of Titan's aerosols. , 1992, Icarus.

[35]  J. Nuth,et al.  The vacuum ultraviolet spectra of HCN, C2N2, and CH3CN , 1982 .

[36]  J. Bowman,et al.  Experimental and reduced dimensionality quantum rate coefficients for H2(D2)+CN→H(D)CN+H(D) , 1990 .

[37]  T. Owen,et al.  Titan: Discovery of Carbon Monoxide in Its Atmosphere , 1983, Science.

[38]  Charles A. Barth.  Nitric oxide in the lower thermosphere , 1992 .

[39]  E. Chassefière,et al.  Formation and growth of photochemical aerosols in Titan's atmosphere , 1992 .

[40]  F. Raulin,et al.  Microphysical modeling of titan's aerosols: Application to the in situ analysis , 1990 .

[41]  A. Coustenis,et al.  Titan's atmosphere from voyager infrared observations: I. The gas composition of Titan's equatorial region , 1989 .

[42]  S. Sandford,et al.  The condensation and vaporization behavior of H2O:CO ices and implications for interstellar grains and cometary activity , 1988 .

[43]  Carl Sagan,et al.  Production and condensation of organic gases in the atmosphere of Titan , 1984 .

[44]  J. Pinto,et al.  Photochemical Production of Formaldehyde in Earth's Primitive Atmosphere , 1980, Science.

[45]  R. Samuelson,et al.  Thermal infrared properties of Titan's stratospheric aerosol , 1991 .

[46]  M. Allen,et al.  Hydrocarbon nucleation and aerosol formation in Neptune's atmosphere. , 1992, Icarus.

[47]  Xun Zhu,et al.  Titan's upper atmosphere - Structure and ultraviolet emissions , 1992 .

[48]  W. A. Payne,et al.  Temperature dependence of the reaction of nitrogen atoms with methyl radicals , 1989 .

[49]  J. Pollack,et al.  Size estimates of Titan's aerosols based on Voyager high-phase-angle images , 1983 .

[50]  R. Yelle.  Non-LTE models of Titan's upper atmosphere , 1991 .

[51]  E. Lellouch,et al.  Carbon Monoxide Outgassing from Comet P/Schwassmann-Wachmann 1 , 1995 .

[52]  J. Pollack,et al.  Titan aerosols: Optical properties and vertical distribution , 1980 .

[53]  Sushil K. Atreya,et al.  Book-Review - Atmospheres and Ionospheres of the Outer Planets and Their Satellites , 1986 .

[54]  M. Allen,et al.  Neptune's visual albedo variations over a solar cycle: A pre-Voyager look at ion-induced nucleatlon and cloud formation in Neptune's troposphere , 1989 .

[55]  J. Pollack,et al.  Vertical distribution of scattering hazes in Titan's upper atmosphere , 1983 .

[56]  J. Lunine,et al.  Ethane Ocean on Titan , 1983, Science.

[57]  A. Aikin,et al.  C4H2, HC3N and C2N2 in Titan's atmosphere , 1981, Nature.

[58]  Marcel Nicolet.  The photodissociation of water vapor in the mesosphere , 1981 .

[59]  P. R. Ratcliff,et al.  Ablation and chemistry of meteoric materials in the atmosphere of Titan. , 1996, Advances in space research : the official journal of the Committee on Space Research.

[60]  H. Okabe.  Photochemistry of acetylene at 1470 A , 1981 .

[61]  E. Lellouch,et al.  The vertical Distribution and Origin of HCN in Neptune's Atmosphere , 1994 .

[62]  M. Molina,et al.  Chemical kinetics and photochemical data for use in stratospheric modeling , 1985 .

[63]  C. McKay,et al.  The thermal structure of Titan's atmosphere. , 1989, Icarus.

[64]  G. Marston,et al.  Structure, spectroscopy and kinetics of the methylene amidogen (H2CN) radical , 1990 .

[65]  L. Horn,et al.  Infrared observations of the saturnian system from voyager 1. , 1981, Science.

[66]  B. Bézard,et al.  Stratospheric profile of HCN on Titan from millimeter observations , 1989 .

[67]  A. Snelson,et al.  Alkylperoxy and alkyl radicals. 4. Matrix IR spectra and UV photolysis of ethylperoxy and ethyl radicals , 1987 .

[68]  D. Muhleman,et al.  CO on Titan: Evidence for a Well-Mixed Vertical Profile , 1995 .

[69]  M. Allen,et al.  Photochemistry of the atmosphere of Titan: comparison between model and observations. , 1984, The Astrophysical journal. Supplement series.

[70]  Kinetic studies of the reactions of methyleneaminylium and dideuteromethyleneaminylium radicals with nitrogen and hydrogen atoms , 1990 .

[71]  R. Courtin,et al.  UV spectroscopy of Titan's atmosphere, planetary organic chemistry, and prebiological synthesis: I. Absorption spectra of gaseous propynenitrile and 2-butynenitrile in the 185- to 250-nm region , 1989 .

[72]  R. Rodrigo,et al.  A nonsteady one‐dimensional theoretical model of Mars' neutral atmospheric composition between 30 and 200 km , 1990 .

[73]  C P McKay,et al.  Photochemical modeling of Titan's atmosphere , 1995, Icarus.

[74]  F. Hirayama,et al.  Fluorescence of acetylenic hydrocarbons , 1979 .

[75]  D. Gautier,et al.  The millimeter spectrum of Titan: detectability of HCN, HC3N, and CH3CN and the CO abundance , 1984 .

[76]  Y. Yung,et al.  Computations and estimates of rate coefficients for hydrocarbon reactions of interest to the atmospheres of the outer solar system , 1983 .

[77]  M. Molina,et al.  Tables of rate constants extracted from chemical kinetics and photochemical data for use in stratospheric modeling. Evaluation number 7 , 1985 .

[78]  L. Giver,et al.  Inhomogeneous models of Titan's aerosol distribution , 1984 .

[79]  D. Gautier,et al.  Abundance of carbon monoxide in the stratosphere of Titan from millimeter heterodyne observations , 1988 .

[80]  K. Watanabe,et al.  Absorption Coefficients of Ethylene in the Vacuum Ultraviolet , 1953 .

[81]  H. Okabe.  Photochemistry of acetylene at 1849 Å , 1983 .

[82]  R. Reid,et al.  The Properties of Gases and Liquids , 1977 .

[83]  D. Muhleman,et al.  Microwave Measurements of Carbon Monoxide on Titan , 1984, Science.

[84]  W. Demore,et al.  Temperature and pressure dependence of CO2 extinction coefficients , 1972 .

[85]  F. Raulin.  Organic chemistry in the oceans of Titan , 1987 .

[86]  D. Strobel.  The photochemistry of hydrocarbons in the atmosphere of Titan , 1974 .

[87]  H. Okabe,et al.  Photochemistry of diacetylene , 1987 .

[88]  J. W. Chamberlain.  Theory of planetary atmospheres , 1978 .

[89]  Michael J. Pilling,et al.  Study of the recombination reaction methyl + methyl .fwdarw. ethane. 1. Experiment , 1988 .

[90]  W. R. Thompson,et al.  Plasma discharge in N2 + CH4 at low pressures: experimental results and applications to Titan. , 1991, Icarus.

[91]  D. Strobel.  Chemistry and evolution of Titan's atmosphere , 1982 .

[92]  Y. Yung,et al.  CO2 on Titan , 1983 .

[93]  D. Strobel,et al.  Titan's upper atmosphere: Composition and temperature from the EUV solar occultation results , 1982 .

[94]  C. McKay,et al.  Methane rain on Titan , 1988 .

[95]  C. McKay,et al.  Surface-atmosphere interactions on Titan compared with those on the pre-biotic Earth. , 1995, Advances in space research : the official journal of the Committee on Space Research.

[96]  W. M. Haynes.  CRC Handbook of Chemistry and Physics , 1990 .