Measurements of positive ion conversion and removal reactions relating to the Jovian ionosphere     

Rainer Johnsen  Manfred A. Biondi 《Icarus》1974,23(2):139-143

Measured rates are presented for the reaction of He⁺ ions with H₂ (and D₂) molecules to form H⁺, H₂⁺, and HeH⁺ ions, as well as for the subsequent reactions of H⁺ and HeH⁺ ions with H₂ to form H₃⁺. The neutralization of H₃⁺ (and H₅⁺) ions by dissociative recombination with electrons is shown to be fast. The reaction He⁺ + H₂ is slow (k = 1.1 × 10^?13 cm³/sec at300°K) and produces principally H⁺ by the dissociative charge transfer branch. It is concluded that there may be a serious bottleneck in the conversion of two of the primary ions of the upper Jovian ionosphere, H⁺ and He⁺ (which recombine slowly), to the rapidly recombining H₃⁺ ion (α[H₃⁺]?3.4 × 10^?7 cm³/sec at 150°K).  相似文献   

Jovian ionospheric models     

L.A. Capone  S.S. Prasad 《Icarus》1973,20(2):200-212

This paper reports results obtained on ionosphere formation in the Jovian upper atmosphere with special reference to some of the recently available reaction rates, and to recent models of the Jovian neutral atmosphere based on the possibility of a warmer mesopause. We find that the role of the hypothetical radiative association of H⁺ to H₂ to form H₃⁺, as brought to light in our earlier study, is still important, even with a reaction rate as low as 10^?15 cm³sec^?1. In the lower regions of the ionosphere three-body processes leading to the formation of H₃⁺ and H₅⁺ ions, which have very fast dissociative recombination rates, produce a dramatic reduction in the electron density. When no radiative association takes place, and the H⁺ ions are lost by radiative recombination alone, we confirm that the photochemical equilibrium profile is also the diffusive equilibrium profile. However, with collisional-radiative recombination, whose rate becomes altitude-dependent, diffusion tends to bring about some redistribution of the ionization. Inclusion of radiative association enhances the role of diffusion. In this case, diffusion brings about all the expected changes. In particular, the differences in the electron density profile, originated in the lower-middle ionosphere by radiative association, are propagated up to all higher altitudes by diffusion. The rate constant of radiative association is, however, unknown. It is hoped that the critical importance of this reaction for the Jovian ionosphere will be an incentive towards a careful laboratory determination of its rate coefficient. In the older models of the Jovian ionosphere the major ions were H⁺ which were lost only by pure radiative recombination. This led to high electron densities and practically no diurnal change. In contrast, our new models have relatively much smaller electron densities, especially in lower regions, and may be susceptible to significant diurnal variation.  相似文献   

The Jovian ionosphere: Composition and temperatures     

S.S. PrasadL.A. Capone 《Icarus》1971

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The upper ionosphere of Titan     

R.C. Whitten  L.A. Capone  L. McCulley  P.F. Michelson 《Icarus》1977,31(1):89-96

Photoionization of the upper atmosphere of Titan by sunlight is expected to produce a substantial ionospheric layer. We have solved one-dimensional forms of the mass, momentum, and energy conservation equations for ions and electrons and have obtained electron number densities of about 10³ cm^?3, using various model atmospheres. The significant ions in a CH₄H₂ atmosphere are H⁺, H₃⁺, CH₅⁺, CH₅⁺, CH₃⁺, and C₂H₅⁺. Electron temperatures may be as high as 1000°K, depending on the abundance of hydrogen in the high atmosphere. Interaction of the solar wind with the ionosphere is also discussed.  相似文献   

Possible H2staggered+ ultraviolet spectrum of Jupiter     

Charles L. Beckel  M. Shafi  Charles L. Hyder 《Icarus》1974,22(2):220-223

An ultraviolet spectral probe for a hydrogen-rich planetary atmosphere, such as that of Jupiter, is suggested, utilizing discrete lines in the H₂^staggered+ 2pπ_u?1sσ_g electronic transition. For the Jovian atmosphere, the dominant mechanism for exciting H₂⁺ to its 2pπ_u state appears to be photoexcitation, principally through absorption of the solar Lyman-α line. We estimate that the Jovian column emission rate of the H₂⁺ 2pπ_u(ν′ = 2, J′ = 1) →1sσ_g(ν″ = 18,J″ = 0) fluorescent line at 1236.6 Å is if1 photon cmsu-2 secsu-1; i.e., that if1 photon secsu-1 of this radiation would strike a 15-cm diameter mirror in a Jupiter fly-by at an impact parameter of 3 × 10⁵km. The critical role of corrections to the Born-Oppenheimer approximation in the use of an H₂⁺ probe is discussed.  相似文献   

Modeling of global variations and ring shadowing in Saturn's ionosphere     

L.E. Moore  I.C.F. Müller-Wodarg  D.L. Murr 《Icarus》2004,172(2):503-520

A time-dependent one-dimensional model of Saturn's ionosphere has been developed as an intermediate step towards a fully coupled Saturn Thermosphere-Ionosphere Model (STIM). A global circulation model (GCM) of the thermosphere provides the latitude and local time dependent neutral atmosphere, from which a globally varying ionosphere is calculated. Four ion species are used (H⁺, H⁺₂, H⁺₃, and He⁺) with current cross-sections and reaction rates, and the SOLAR2000 model for the Sun's irradiance. Occultation data from the Voyager photopolarimeter system (PPS) are adapted to model the radial profile of the ultraviolet (UV) optical depth of the rings. Diurnal electron density peak values and heights are generated for all latitudes and two seasons under solar minimum and solar maximum conditions, both with and without shadowing from the rings. Saturn's lower ionosphere is shown to be in photochemical equilibrium, whereas diffusive processes are important in the topside. In agreement with previous 1-D models, the ionosphere is dominated by H⁺ and H⁺₃, with a peak electron density of ∼¹⁰⁴ electrons cm⁻³. At low- and mid-latitudes, H⁺ is the dominant ion, and the electron density exhibits a diurnal maximum during the mid-afternoon. At higher latitudes and shadowed latitudes (smaller ionizing fluxes), the diurnal maximum retreats towards noon, and the ratio of [H⁺]/[H⁺₃] decreases, with H⁺₃ becoming the dominant ion at altitudes near the peak (∼1200-1600 km) for noon-time hours. Shadowing from the rings leads to attenuation of solar flux, the magnitude and latitudinal structure of which is seasonal. During solstice, the season for the Cassini spacecraft's encounter with Saturn, attenuation has a maximum of two orders of magnitude, causing a reduction in modeled peak electron densities and total electron column contents by as much as a factor of three. Calculations are performed that explore the parameter space for charge-exchange reactions of H⁺ with vibrationally excited H₂, and for different influxes of H₂O, resulting in a maximum diurnal variation in electron density much weaker than the diurnal variations inferred from Voyager's Saturn Electrostatic Discharge (SED) measurements. Peak values of height-integrated Pedersen conductivities at high latitudes during solar maximum are modeled to be ∼42 mho in the summer hemisphere during solstice and ∼18 mho during equinox, indicating that even without ionization produced by auroral processes, magnetosphere-ionosphere coupling can be highly variable.  相似文献   

Dynamical behavior of thermal protons in the mid-latitude ionosphere and magnetosphere     

P.M. Banks  A.F. NagyW.I. Axford 《Planetary and Space Science》1971

Satellite and other observations have shown that H⁺ densities in the mid-latitude topside ionosphere are greatly reduced during magnetic storms when the plasmapause and magnetic field convection move to relatively low L-values. In the recovery phase of the magnetic storm the convection region moves to higher L-values and replenishment of H⁺ in the empty magnetospheric field tubes begins. The upwards flow of H⁺, which arises from O⁺—H charge exchange, is initially supersonic. However, as the field tubes fill with plasma, a shock front moves downwards towards the ionosphere, eventually converting the upwards flow to subsonic speeds. The duration of this supersonic recovery depends strongly on the volume of the field tube; for example calculations indicate that for L = 5 the time is approximately 22 hours. The subsonic flow continues until diffusive equilibrium is reached or a new magnetic storm begins. Calculations of the density and flux profiles expected during the subsonic phase of the recovery show that diffusive equilibrium is still not reached after an elapsed time of 10 days and correspondingly there is still a net loss of plasma from the ionosphere to the magnetosphere at that time. This slow recovery of the H⁺ density and flux patterns, following magnetic storms, indicates that the mid-latitude topside ionosphere may be in a continual dynamic state if the storms occur sufficiently often.  相似文献   

The role of hydrocarbons in the lonospheres of the outer planets     

S.K. Atreya  T.M. Donahue 《Icarus》1975,25(2):335-338

The role of hydrocarbons as a possible sink for H⁺ and H₃⁺ ions in the lower ionosphere of the outer planets is examined. Calculations indicate that H⁺ and H₃⁺ are efficiently converted to hydrocarbon ions on reaction with methane. The terminal ions, CH₅⁺ and C₂H₅⁺ are rapidly neutralized in dissociative recombination with electrons. Extreme ultraviolet photolysis of hydrocarbons as a potential additional source of lower elevation ions in investigated.  相似文献   

Ion chemistry in the cometary atmosphere     

Mikio Shimizu 《Astrophysics and Space Science》1975,36(2):353-361

Dirty ice of a second kind (major components, H₂O, CO, and N₂; minor components less than several percents, NH₃, CH₄, and other organic substances such as HCN, CH₃CN etc.) is assumed for the composition of volatiles in the cometary nucleus. The consistency with the observations of molecular ions and daughter molecules in the cometary atmosphere is argued by taking into account various ion-molecular reactions and dissociative recombinations. There is a satisfactory agreement for the second kind of dirty-ice model, but the presence of large amounts of CH₄ and NH₃ is found to be rather in contradiction with observational evidence. A velocity of 8 km s^?1 for the hydrogen atoms, derived from analysis of the hydrogen Lyman-alpha corona around comets, is found from the dissociative recombination of H₃O⁺, the dominant constituent of cometary ionosphere, in accordance with H₃O⁺+e ^?→OH+H+H.  相似文献   

Mid-latitude electron content modelling: The role of interhemispheric coupling     

G.C. Sethia  G.J. Bailey  R.J. Moffett  J.K. Hargreaves 《Planetary and Space Science》1985,33(3):321-332

A modelling study of the electron content of the mid-latitude ionosphere and protonosphere has been carried out for solstice conditions using the mathematical model of Bailey (1983). In the model calculations coupled time-dependent O⁺, H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved for a magnetic shell extending over both hemispheres. The inclusion of interhemispheric flow of plasma and of heat balance has enabled us to investigate the role of interhemispheric coupling on the electron content and related shape parameters. The computed results are compared with results from slant path observations of the ATS-6 radio beacon made at Lancaster (U.K.) and Boulder, Colorado (U.S.A.).It has been found that the conjugate photoelectron heating has a major effect on the shape of the daily variation of slant slab thickness (τ) and also on the magnitude of the protonospheric content (N_p). Some of the main features of τ are closely related to the sunrise and sunset times in the conjugate ionosphere. Also it is found that night-time increases in total electron content (N_T) and F2 region peak electron density (N_max) in winter are natural consequences of ionization loss at low altitudes causing an enhanced downward flow of plasma from the protonosphere which is coupled to the summer hemisphere. One other important consequence of the coupled protonosphere is that the effects on N_T of the neutral air wind are not much different in winter from those in summer.  相似文献   

Flowing afterglow studies of temperature dependencies for electron dissociative recombination of HCNH, CH₃CNH and CH₃CH₂CNH and their symmetrical proton-bound dimers     

J.L. McLain 《Planetary and Space Science》2009,57(13):1642-39

A study has been made using a variable temperature flowing afterglow Langmuir probe technique (VT-FALP) to determine the equilibrium temperature dependencies of the dissociative electron-ion recombination of the protonated cyanide ions (RCNH⁺, where R=H, CH₃ and C₂H₅) and their symmetrical proton-bound dimers (RCNH⁺NCR). The power law temperature dependencies of the recombination coefficients, α_e, over the temperature range 180 to 600 K for the protonated ions are α_e(T)(cm³ s⁻¹)=3.5±0.5×10⁻⁷ (300/T)^1.38 for HCNH⁺, α_e(T)=3.4±0.5×10⁻⁷ (300/T)^1.03 for CH₃CNH⁺, and α_e(T)=4.6±0.7×10⁻⁷ (300/T)^0.81 for CH₃CH₂CNH⁺. The equivalent values for the proton-bound dimers are α_e(T)(cm³ s⁻¹)=2.4±0.4×10⁻⁶(300/T)^0.5 for (HCN)₂H⁺ to α_e(T)=2.8±0.4×10⁻⁶(300/T)^0.5 for (CH₃CN)₂H⁺, and α_e(T)=2.3±0.3×10⁻⁶(300/T)^0.5 for (CH₃CH₂CN)₂H⁺. The relevance of these data to molecular synthesis in the interstellar medium and the Titan ionosphere are discussed.  相似文献   

A fast computation of the diurnal secondary ion production in the ionosphere of Titan     

Jean Lilensten  Cyril Simon  Odile Dutuit  Christian Alcaraz 《Icarus》2005,174(1):285-288

We propose an analytic model that allows rapid computation of the secondary ion production due to electron impact from the primary photo-production in the ionosphere of Titan. The model parameters are given for each of the 5 major ion productions (N⁺₂, CH⁺₄, N⁺, CH⁺₃, N⁺⁺₂) as well as for the electron production.  相似文献   

Cross-section for the dissociative photoionization of hydrogen by 584 Å radiation: The formation of protons in the Jovian ionosphere     

K.M. Monahan  W.T. Huntress  A.L. Lane  J.M. Ajello  T.E. Burke  P. Le Breton  A. Williamson 《Planetary and Space Science》1974,22(1):143-149

The cross-section for dissociative photoionization of hydrogen by 584 Å radiation has been measured, yielding a value of 5 × 10^?20 cm². The process can be explained as a transition from the $\text{X}{}^1\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ ground state to a continuum level of the $\text{X}{}^2\text{Σ}{}_{\mathrm{g}}{}^{\mathrm{+}}$ ionized state of H₂ The branching ratio for proton (H⁺) vs molecular ion (H₂⁺) production at this energy is 8 × 10^?3. This process is quite likely an important source of protons in the Jovian ionosphere near altitudes where peak ionization rates are found.  相似文献   

The lower ionosphere of Titan     

L.A. Capone  R.C. Whitten  J. Dubach  S.S. Prasad  W.T. Huntress 《Icarus》1976,28(3):367-378

Ionization of the atmosphere of Titan by galactic cosmic rays is a very significant process throughout the altitude range of 100 to 400 km. An approximate form of the Boltzmann equation for cosmic ray transport has been used to obtain local ionization rates. Models of both ion and neutral chemistry have been employed to compute electron and ion density profiles for three different values of the H₂/CH₄ abundance ratio. The peak electron density is of the order 10³ cm^?3. The most abundant positive ions are C₂H₉⁺ and C₃H₉⁺, while the predicted densities of the negative ions H^? and CH₃^? are very small (<10^?4 that of the positive ions). It is suggested that inclusion of the ion chemistry is important in the computation of the H and CH₃ density profiles in the lower ionosphere.  相似文献   

Silicon ion chemistry in the ionosphere     

E.E. Ferguson  D.W. Fahey  F.C. Fehsenfeld  D.L. Albritton 《Planetary and Space Science》1981,29(3):307-312

Loss processes which remove Si⁺ ions selectively relative to other meteor-derived atomic ions in the E- and D-regions of the ionosphere have been identified and measured in the laboratory. The major Si⁺ loss in the E-region is the reaction Si⁺ + H₂O → HSiO⁺ + H (1) with a rate constant 2.3 ± 0.9 × 10^?10 cm³s^?1 at 300 K. The corresponding reactions with Fe⁺, Mg⁺ and other metallic meteor ions are endothermic. Presumably (1) is followed by a fast dissociative-recombination with electrons to produce neutral SiO or Si. At lower altitudes Si⁺ ions associate in a three-body reaction with O₂ with a much larger rate constant than the corresponding associations of Fe⁺ and Mg⁺ with O₂.  相似文献   

Cosmic ray ionization of the Jovian atmosphere     

Louis A. Capone  John Dubach  Robert C. Whitten  Sheo S. Prasad 《Icarus》1979,39(3):433-449

An approximate form of the Boltzmann equation has been used to obtain local ionization rates due to the absorption of galactic cosmic rays in the Jovian atmosphere. It is shown that the muon flux component of the cosmic ray-induced cascade may be especially importannt in ionizing the atmosphere at levels where the total number density exceeds 10¹⁹ cm^?3 (well below the ionospheric layers produced by solar euv). A model containing both positive and negative ion reactions has been employed to compute equilibrium electron and ion number densities. Peak electron number densities on the order of 10³ cm^?3 may be expected even at relatively low magnetic latitudes. The dominant positive ions are NH₄⁺ and C_nH_m⁺ cluster ions, with n ? 2; it is suggested that the absorption of galactic cosmic ray energy at such relatively high pressures in the Jovian atmosphere $\text{(M ? 10}{}^{18}\text{to}\text{10}{}^{20}\text{cm}{}^{\mathrm{?3}}\text{)}$ and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.  相似文献   

Ion composition and chemistry in the coma of Comet 1P/Halley—A comparison between Giotto's Ion Mass Spectrometer and our ion-chemical network     

Martin Rubin  Kenneth C. Hansen  Michael R. Combi  Hans Balsiger 《Icarus》2009,199(2):505-519

In order to understand the cometary plasma environment it is important to track the closely linked chemical reactions that dominate ion evolution. We used a coupled MHD ion-chemistry model to analyze previously unpublished Giotto High Intensity Ion Mass Spectrometer (HIS-IMS) data. In this way we study the major species, but we also try to match some minor species like the CH_x and the NH_x groups. Crucial for this match is the model used for the electrons since they are important for ion-electron recombination. To further improve our results we included an enhanced density of supersonic electrons in the ion pile-up region which increases the local electron impact ionization. In this paper we discuss the results for the following important ions: C⁺, CH⁺, CH⁺₂, CH⁺₃, N⁺, NH⁺, NH⁺₂, NH⁺₃, NH⁺₄, O⁺, OH⁺, H₂O⁺, H₃O⁺, CO⁺, HCO⁺, H₃CO⁺, and CH₃OH⁺₂. We also address the inner shock which is very distinctive in our MHD model as well as in the IMS data. It is located just inside the contact surface at approximately 4550 km. Comparisons of the ion bulk flow directions and velocities from our MHD model with the data measured by the HIS-IMS give indication for a solar wind magnetic field direction different from the standard Parker angle at Halley's position. Our ion-chemical network model results are in a good agreement with the experimental data. In order to achieve the presented results we included an additional short lived inner source for the C⁺, CH⁺, and CH⁺₂ ions. Furthermore we performed our simulations with two different production rates to better match the measurements which is an indication for a change and/or an asymmetric pattern (e.g. jets) in the production rate during Giotto's fly-by at Halley's comet.  相似文献   

The topside ionosphere above Arecibo at equinox during sunspot maximum     

G.J. Bailey 《Planetary and Space Science》1980,28(1):47-59

The coupled time-dependent O⁺ and H⁺ continuity and momentum equations and O⁺, H⁺ and electron heat balance equations are solved simultaneously within the L = 1.4 (Arecibo) magnetic flux tube between an altitude of 120 km and the equatorial plane. The results of the calculations are used in a study of the topside ionosphere above Arecibo at equinox during sunspot maximum. Magnetically quiet conditions are assumed.The results of the calculations show that the L = 1.4 magnetic flux tube becomes saturated from an arbitrary state within 2–3 days. During the day the ion content of the magnetic flux tube consists mainly of O⁺ whereas O⁺ and H⁺ are both important during the night. There is an altitude region in the topside ionosphere during the day where ion-counterstreaming occurs with H⁺ flowing downward and O⁺ flowing upward. The conditions causing this ion-counterstreaming are discussed. There is a net chemical gain of H⁺ at the higher altitudes. This H⁺ diffuses both upwards and downwards whilst O⁺ diffuses upwards from its solar e.u.v. production source which is most important at the lower altitudes. During the night the calculated O⁺ and H⁺ temperatures are very nearly equal whereas during the day there are occasions when the H⁺ temperature exceeds the O⁺ temperature by about 300 K.  相似文献   

The topside equatorial ionosphere during daytime: Elevated plasma temperatures,the transequatorial O⁺ breeze and the dynamics of minor ions     

G.I. Bailey  R.I. Moffett 《Planetary and Space Science》1979,27(8):1075-1085

Steady-state calculations are performed for the daytime equatorial F2-region and topside ionosphere. Values are calculated of the electron and ion temperatures and the concentrations and field-aligned velocities of the ions O⁺, H⁺ and He⁺. Account is taken of upward $\text{E × B}$ drift, a summer-winter horizontal neutral air wind and heating of the electron gas by thermalization of fast photoelectrons.The calculated plasma temperatures are in accord with experiment: at the equator there is an isothermal region from about 400–550 km altitude, with temperatures of about 2400 K around 800 km altitude. The transequatorial O⁺ breeze flux from summer to winter in the topside ionosphere is not greatly affected by the elevated plasma temperatures. The field-aligned velocities of H⁺ and He⁺ depend strongly on the O⁺ field-aligned velocity and on the presence of large temperature gradients. For the minor ions, ion-ion drag with O⁺ cannot be neglected for the topside ionosphere.  相似文献   

Hydrogen on venus: Exospheric distribution and escape     

J.M. Rodriguez  M.J. Prather  M.B. McElroy 《Planetary and Space Science》1984,32(10):1235-1255

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