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1.
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 ground state to a continuum level of the 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
2.
Kjell Henriksen 《Planetary and Space Science》1973,21(5):863-871
The part that the energy transfer reaction plays in the excitation of the auroral green line has been investigated. The contribution is estimated to be 40 per cent in this case, containing pulsating aurora in class IBC 1. Due to greater quenching of the A3∑u+ state, the centroid of the VK emission is displaced 10 km upwards of the green line height, which is centred at 110 km. 相似文献
3.
The quenching rate kN2 of by N2 and the specific recombination rate α1D of O2+ leading to are re-examined in light of available laboratory and satellite data. Use of recent experimental values for the transition probabilities in a re-analysis of AE-C satellite 6300 Å airglow data results in a value for kN2 of 2.3 × 10?11 cm3s?1 at thermospheric temperatures, in excellent agreement with the laboratory measurements. This implies a value of JO2 = 1.5 × 10?6s?1 for the O2 photodissociation rate in the Schumann-Runge continuum. The specific recombination coefficient α1D = 2.1 × 10?7cm3s?1 is also in agreement with the laboratory value. Implications for the suggested reaction are discussed. 相似文献
4.
A mechanism has been proposed for uv-accelerated desorption from Fe2+ sites on mineral surfaces that satisfies kinetic constraints determined in the laboratory by Huguenin. The process is an integral step of the photochemical weathering mechanism for producing dust on Mars, and it now appears that it may play primary roles in stabilizing CO2 against dissociation by sunlight and in controlling the oxidation state of the atmosphere. We propose that adsorption occurs at octahedrally coordinated Fe2+ surface sites to form seven-coordinate transition-state complexes. These complexes acquire 16–18 kcal mole?1 of ligand field stabilization energy. During illumination (λ ≤ 0.35 μm), electrons are photoemitted from the surfaced Fe2+, temporarily oxidizing them to Fe3+. Fe3+ has no ligand field stabilization energy, and the complexes lose 16–18 kcal mole?1 of stabilization energy. This is a large fraction of the 19- to 28-kcal mole?1 activation energy for dissociating the complexes, and desorption should proceed spontaneously. The gases that were observed to undergo adsorption-photodesorption include O2, CO2, CO, H2O, N2, and Ar. Photodesorption can drive several catalytic reactions, one of which is the oxidation of CO to CO2. The rate of this reaction should be limited by the supply of CO and O2 to the surface to ～2 × 1012 cm?2 sec?1 (column photodissociation rate of CO2). By including this surface reaction in models of Martian atmospheric CO2 chemistry, CO2 can be stabilized against photodissociation with eddy diffusion coefficients of only 3 × 105?1 × 107 cm2 sec?1 below 40 km, raising to ～ 109 cm2 sec?1 at 140 km. Odd hydrogen is not needed to catalyze the oxidation of CO below 40 km, and odd hydrogen mixing ratios need only to be to depress ozone concentrations below the observed upper limit in equatorial regions. Another catalytic reaction that should be driven by photodesorption on Mars is . This is an important source of atmospheric O2, amounting to 7 × 1013?2 × 1017 O2 molecules cm?2 yr?1, and it could have a significant effect on atmospheric oxidation state. 相似文献
5.
The calculated radiative lifetime of the metastable ion is 6.4 × 10?3s. Used in conjunction with the results of measurements by Erdman, Espy and Zipf this sets 1.3 × 10?18 cm2 as the upper limit to the cross section for the formation of in e - N2 collisions at 100eV which leaves the possibility that the process is responsible for the feature in auroras only just open. The cross section for the formation of in e — N collisions is large. However for this process to lead to the observed intensity of relative to the N:N2 abundance ratio would have to be as high as 1.6 × 10?2. 相似文献
6.
Measurements of N2+ and supporting data made on the Atmosphere Explorer-C satellite in the ionosphere are used to study the charge exchange process The equality k = (5 ± 1.7) × 10?10cm3s?1. This value lies close to the lower limit of experimental uncertainty of the rate coefficient determined in the laboratory. We have also investigated atomic oxygen quenching of O+(2D) and find that the rate coefficient is 2 × 10?11 cm3s?1 to within approximately a factor of two. 相似文献
7.
W. Swider 《Planetary and Space Science》1983,31(1):49-52
For nighttime auroras, we find that positive ion ratios are only a function of the neutral atmospheric composition and of the pertinent ionic processes if the ions are depleted mainly by ion-molecule reactions. Ionic ratios calculated for using the 1976 U.S. Standard Atmosphere and laboratory rate coefficients (with one exception) rise smoothly with altitude: 0.1 (120 km), 0.3 (140 km), 0.6 (160 km), 1.0 (180 km) and 1.5 (200 km). These values compare favorably with experimental ratios from three different auroral experiments. The exception refers to our use of a larger rate coefficient for N2+ + O → NO+ + N than found in the laboratory. We also determine an ratio with altitude: 0.36 (120 km), 0.078 (140 km), 0.030 (160 km), 0.014 (180 km) and 0.0075 (200 km). These values compare favorably with results from the same three auroral experiments. However, the match with a fourth auroral experiment is poor. Except for this last case, we conclude that the neutral composition at auroral latitudes in late winter is similar to the U.S. Standard for the altitudes examined. 相似文献
8.
Laboratory cross-section data on the excitation of the OII(2s 2p44P → 2s2 2p34S; λ834 Å) resonance transition and on the production of O+ and O2+ ions by electron impact on atomic oxygen are used to show that the ratio is nearly constant for incident electron energies > 50 eV. Under auroral conditions, the total electron-ion pair production rate from electron impact on O can be inferred from λ834 Å volume emission rate measurements using the result that . These findings, along with earlier work on the simultaneous ionization-excitation of the 1 Neg (0,0) band of N2+ and the 1 Neg (1, 0) band of O+2, allow the specific ionization rates for the principal atmospheric constituents (O+, O+2, N+2), for the multiply-ionized species (O2+, O2+2, N2+2), and for the dissociatively produced atomic ions to be inferred in aurora from remote satellite observations. 相似文献
9.
Recent laboratory studies show that the quantum yield, , from O2+ dissociative recombination varies considerably with the degree r of vibrational excitation. However, the suggestion that the high values for deduced from airglow and auroral observations can be explained by invoking vibrational excitation, creates a number of problems. Firstly, the rapid vibrational deactivation of O2+ ions by collisions with O atoms will keep r too low to account for the magnitude of ; secondly, r varies considerably from one atmospheric source to another but its relative values (which should be reliable) do not co-vary with those of ; thirdly, because r increases markedly above the peak of the dissociative recombination layer, the fits which theorists have obtained to the observed volume emission rate profiles would have to be regarded as fortuitious. It is tentatively suggested that is higher in the airglow and aurora than in the laboratory plasma studied by Zipf (1980) because of the electron temperature dependence of the specific recombination coefficient for O2+(v' ? 3) ions.The repulsive state of O2 does not provide a suitable channel for the dissociative recombination. A possible alternative is the bound state with predissociation to the repulsive state. 相似文献
10.
Marcel Nicolet 《Planetary and Space Science》1984,32(7):871-880
The photodissociation of water vapour in the mesosphere depends on the absorption of solar radiation in the region (175–200 nm) of the O2 Schumann-Runge band system and also at H-Lyman alpha. The photodissociation products are OH + H, OH + H, O + 2H and H2 + O at Lyman alpha; the percentages for these four channels are 70, 8, 12 and 10%, respectively, but OH + H is the only channel between 175 and 200 nm. Such proportions lead to a production of H atoms corresponding to practically the total photodissociation of H2O, while the production of H2 molecules is only 10% of the H2O photodissociation by Lyman alpha.The photodissociation frequency (s?1) at Lyman alpha can be expressed by a simple formula where F10.7 cm is the solar radioflux at 10.7 cm and N the total number of O2 molecules (cm?2), and when the following conventional value is accepted for the Lyman alpha solar irradiance at the top of the Earth's atmosphere () qLyα,∞ = 3 × 1011 photons cm?2 s1?.The photodissociation frequency for the Schumann-Runge band region is also given for mesospheric conditions by a simple formula where JSRB,∞(H2O) = 1.2 × 10?6 and 1.4 × 10?6 s?1 for quiet and active sun conditions, respectively.The precision of both formulae is good, with an uncertainty less than 10%, but their accuracy depends on the accuracy of observational and experimental parameters such as the absolute solar irradiances, the variable transmittance of O2 and the H2O effective absorption cross sections. The various uncertainties are discussed. As an example, the absolute values deduced from the above formulae could be decreased by about 25-20% if the possible minimum values of the solar irradiances were used. 相似文献
11.
Special line shapes are derived fro the λ 1356 Å () transition of atomic oxygen from metastable () time-of-flight spectra produced by electron impact dissociative excitation of O2, CO2, CO, and NO, and they are compared with the broadened λ 1304 A resonance line shapes deduced by Poland and Lawrence (1973) from atomic oxygen absorption studies. The non-thermal line shapes for both airglow emission features are shown to have an effective width comparable to a 60,000 K thermal doppler line shape for an electron impact energy of 100eV. The variation of the effective line width with electron-impact energy from threshold to 300 eV is given. Since the effective line width of the resonance radiation produced by dissociative excitation is very large compared with the doppler absorption widths of the ambient O atoms at normal exospheric temperatures, the anomalously broadened resonance lines will propagate through a planetary atmosphere as though they were optically thin. Thus, electron-impact dissociation of CO and CO2 will contribute to the observed optically thin component of the λ 1304 Å emission in the upper atmospheres of Venus and Mars. However, the process cannot account for more than 10% of the observed optically thin emission because of the small magnitude of the excitation cross-section and the comparatively high-energy threshold for the process. The possibility that the source of the kinetically energetic ) atoms is the dissociative recombination of vibrationally excited CO2+ ions is discussed. 相似文献
12.
Reactions of metastable species are important in determining the densities of minor ions in the Venusian ionosphere. Calculations are carried out in which the coupled continuity and momentum equations are solved for twelve ions and four neutral species in the dayside ionosphere, including . Altitude profiles of these metastable species are presented. Their reactions are shown to be a significant source of several minor ions, especially N2+, CO+, and N+. The discrepancies which existed between model and measured densities of these ions are resolved. 相似文献
13.
G.G. Shepherd J.F. Pieau T. Ogawa T. Tohmatsu K. Oyama Y. Watanabe 《Planetary and Space Science》1978,26(3):211-217
A sounding rocket was flown during the predawn on 17 January, 1976 from Uchinoura, Japan, to measure directly the behaviour of the conjugate photoelectrons at magnetically low latitudes. On board the rocket were an electron energy analyzer, 630 nm airglow photometer, and plasma probes to measure electron density and temperature. The incoming flux of the photoelectrons was measured in the altitude range between 210 and 340 km. The differential flux at the top of the atmosphere was determined to be electron · m?2 · sr?1 · s?1 in the energy range 10 ? E ? 50 eV. The emission rate of the 630 nm airglow was observed in the altitude range between 90 and 360 km. The apparent emission rate observed at 80 km was 32 ± 5 R. From a theoretical calculation of the optical excitation rate using the observed electron flux data along with a model distribution of atomic oxygen, it was estimated that more than 65% of the emission could be produced by direct impact of the photoelectrons with atomic oxygen in the thermosphere between 200 and 360 km. Using the observed electron density and the model distribution of oxygen molecules the residual of the emission was ascribed to the excitation of O(1D) through dissociative recombination, . The direct collisional excitation by ambient electrons is estimated to be negligibly small at the level of observed electron temperature. 相似文献
14.
W.T. Huntress 《Planetary and Space Science》1975,23(2):377-378
Laboratory data shows that the reaction of protons with methane proceeds at thermal ion energies to give both CH3+ and CH4+ ions in the ratio . The overall rate constant for the reaction is 3.8 ± 0.3 × 10?9 cm3/sec. This reaction may lead to the formation of hydrocarbon ions in the lower ionosphere of Jupiter, and the significance of this process for formation of hydrocarbons and HCN in the atmosphere of Jupiter is discussed. 相似文献
15.
《Chinese Astronomy and Astrophysics》1982,6(1):24-27
Six times of maxima of the ultrashort-period cepheid variable EH Librae were measured in 1980 May to June and in 1981 January, with a three-channel photocounting high-speed photoelectric photometer. These, together with all the photoelectric times of maxima over the past 30 years, are used to re-examine the nature of the change of the period. We found that we can fix the times of maxima by the following formula where T0 = HJD 2433438.6088 and P0 = 0.0884132445 d represent the initial maximum epoch and the pulsation period, β = ?2.8 × 10?8/yr; A = 0.0015 d, P0 = 6251 d = 17.1 yr are the semi-amplitude and the period of the sine curve, and E is the number of periods elapsed since T0, and (E0 = 70700).If we interpret this 17.1 year periodicity as a modulation of the phase of maximum by binary motion, then the semi-amplitude of the orbital radial velocity variation is K = 2πasini/E0 = 0.45 km/s and the mass function is 相似文献
16.
Results are given of the calculations of the group delay time propagating τ(ω, φ0) of hydromagnetic whistlers, using outer ionospheric models closely resembling actual conditions. The τ(ω, φ0) dependencies were compared with the experimental data of τexp(ω, φ0) obtained from sonagrams. The sonagrams were recorded in the frequency range at observation points located at geomagnetic latitudes φ0 = (53?66)° and in the vicinity of the geomagnetic poles. This investigation has led us to new and important conclusions.The wave packets (W.P.) forming hydromagnetic whistlers (H.W.) are mainly generated in the plasma regions at L = 3.5?4.0. This is not consistent with ideas already expressed in the literature that their generation region is . The overwhelming majority of the τexp values differ considerably from the times at which wave packets would, in theory, propagate along the magnetic field lines corresponding to those of the geomagnetic latitudes φ0 of the observation points. The second important fact is that the W.P. frequency ω is less than everywhere along its propagation trajectory, including the apogee of the magnetic force line ( is the proton gyrofrequency). Proton flux spectra keV, responsible for H.W. generation, were determined. Comparison of the Explorer-45 and OGO-3 measurements published in the literature, with our data, showed that the proton flux density energy responsible for the H.W. excitation where Ha is the magnetic field force in the generation region of these W.P. The electron concentration is . The values given in the literature are . The e data considered also leads to the conclusion that the generating mechanism of the W.P. studied probably always co-exists with the mechanism of their amplification. 相似文献
17.
The problem of the theoretical computation of the emission intensities and ion composition in a weak aurora which has been preceded by a stronger event is examined. For this purpose a model auroral precipitation consisting of biexponential primaries is considered. The softer of the two components is brighter, and begins to decay after remaining steady for ten to fifteen minutes. The other, harder component starts to build up at that instant. Our results suggest that at least a part of the high ratios could be attributed to the retention, by the atmosphere, of the memory of previous auroral precipitations. Thus, the serious energy paradox in the context of 1·27 μ intensity need not arise, and, in the context of the large NO+ density, it may perhaps be unnecessary to invoke any major conversion of O2 to NO thus avoiding the associated energy problem. 相似文献
18.
Observations of type-B red and normal aurora were made with a high-speed multichannel photometer and a digital grating spectrometer. The ratio measured in the 5200–5300 Å region with the spectrometer was found to increase by about 16% from normal to type-B aurora. This small change is difficult to reconcile with a height below 90 km for the red border. In the type-B aurora, λ 5577 was weakened by a factor between 1.9 and 3.8 while the ratio was enhanced less than 20%. Rapid intensity variations in the type-B lower border were observed in the λ 5577 and other channels of the photometer. A revised time dependent auroral excitation-ion chemistry model is used in an attempt to reproduce the observations. The observed weakening of λ 5577 could be produced at heights equal to or less than 100 km while the short observed time lag of λ 5577 on the N2+ 1N emission is easier to explain at 100 km than at 80 km. It is concluded that some type-B lower borders may occur near 100 km although it is recognized that there is good evidence rare deep crimson lower borders lie at 80 km or below. The mechanism for the excitation of O(1S) is considered in the light of these results. None of the mechanisms examined is satisfactory on the basis of currently accepted atmospheric models and quenching rate coefficients. 相似文献
19.
Radiative recombination of N and O provides a significant source for auroral emission in the γ and δ bands of NO with selective population of vibrational levels in the A2Σ+ and C2Π states. This mechanism may account for emissions detected near 2150 Å. Models are derived for the auroral ionosphere and include estimates for the concentrations of N and NO. The concentration of NO is estimated to have a value of about 108 cm?1 near 140 km in an IBC III aurora. The corresponding density for N is about 5 × 107cm?3 and the concentration ratio has a value of about 5.5. 相似文献
20.
Kiyohumi Yumoto 《Planetary and Space Science》1985,33(9):1029-1036
We analyze linear resonance oscillations in a non-uniform one-fluid finite-β plasma, which is oversimplified to understand easily fundamental characteristics of the resonance oscillations. A linear resonance oscillation of localized slow magnetosonic mode , which has the diamagnetic property in a uniform plasma, is newly found to be excited in the radially non-uniform plasma. The localized slow resonance indicates a radially polarized compressional oscillation (δB∥ ? δBH ? δBD). The sense of the Alfvénic polarizations in the H-D plane near the resonant point is a function of both the propagation in the azimuthal direction and the slope of wave amplitude in the radial direction, whereas the sense of the resonant slow magnetosonic polarizations changes in accordance only with the switch in the azimuthal propagation direction. Further multi-satellite studies are necessary to establish the resonant structures of the slow magnetosonic waves in the magnetosphere. 相似文献