首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 31 毫秒
1.
Special line shapes are derived fro the λ 1356 Å (5S0-3P) transition of atomic oxygen from metastable (5S0-3P) 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 O(3S) atoms is the dissociative recombination of vibrationally excited CO2+ ions is discussed.  相似文献   

2.
The quenching rate kN2 of O(1D) by N2 and the specific recombination rate α1D of O2+ leading to O(1D) are re-examined in light of available laboratory and satellite data. Use of recent experimental values for the O(1D) 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 N(2D) + O2 → O(1D) + NO reaction are discussed.  相似文献   

3.
The resonant electron impact quenching of metastable molecules might be important for understanding the phenomena in the upper atmosphere. In order to obtain information about the relative importance of this scattering event the resonant cross sections for electron scattering by metastable nitrogen in the A3u+ state were calculated using the “boomerang” model and quenching rates for this state were evaluated for the altitudes of 130,170 and 210km. The obtained quenching rates are small (?5 × 10?3 s?1), even with respect to the radiative transition rate showing that under the considered conditions this process is unimportant for population of nitrogen A3u+ state in the Earth's thermosphere.  相似文献   

4.
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 CnHm+ 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 (M ? 1018to 1020cm?3) and the subsequent chemical reactions may be instrumental in the local formation of complex hydrocarbons.  相似文献   

5.
Recent laboratory studies show that the O(1S) quantum yield, f(1S), from O2+ dissociative recombination varies considerably with the degree r of vibrational excitation. However, the suggestion that the high values for f(1S) 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 f(1S); 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 f(1S); thirdly, because r increases markedly above the peak of the X5577 A? 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 f(1S) is higher in the airglow and aurora than in the laboratory plasma studied by Zipf (1980) because of the electron temperature dependence of the O(1S) specific recombination coefficient for O2+(v' ? 3) ions.The repulsive 1Σu[1D + 1s] state of O2 does not provide a suitable channel for the dissociative recombination. A possible alternative is the bound 3Πu[5S + 3s] state with predissociation to the repulsive 3Πu[3P + 1s] state.  相似文献   

6.
Incoherent scatter observations of the ionospheric F1 layer above Saint-Santin (44.6°N) are analyzed after correction of a systematic error at 165 and 180 km altitude. The daytime valley observed around 200 km during summer for low solar activity conditions is explained in terms of a downward ionization drift which reaches ?30 m s?1 around 180 km. Experimental determinations of the ion drift confirm the theoretical characteristics required for the summer daytime valley as well as for the winter behaviour without a valley. The computations require an effective dissociative recombination rate of 2.3 × 10?7 (300/Te)0.7 (cm3s?1) and ionizing fluxes compatible with solar activity conditions at the time when the valley is observed.  相似文献   

7.
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 F = (1.3 ± 0.4) × 1011exp[?E(eV)12] 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, O2++eO1 + O7. The direct collisional excitation by ambient electrons is estimated to be negligibly small at the level of observed electron temperature.  相似文献   

8.
T.E. Cravens  A.E.S. Green 《Icarus》1978,33(3):612-623
The intensities of radiation from the inner comas of comets which are composed primarily of water and carbon monoxide have been calculated. Only “airglow” emissions initiated by the absorption of extreme ultraviolet radiation have been considered. The photoionizations of H2O, CO, CO2, and N2 are the most important emission sources, although photoelectron excitation is also considered. Among the emission features for which intensities were calculated are H2O+ (A?2A1?X?2B1), CO+ (first negative), CO (fourth positive), CO (Cameron), CO2+ (B?2?u?X?2IIg), N2 (Vegard-Kaplan), N2+ (first negative), and OI (1304 Å). In the inner coma (collision region) these airglow mechanisms are shown to be possible competitors with the usually assumed resonance scattering and flourescence excitation mechanisms which are appropriate for the outer coma and tail.  相似文献   

9.
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 σ(λ834 A?)σ(O+ + O2+) 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 η(O+ + O2+)$?8.4η(λ834 A?). 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   

10.
Numerical solutions of the Fokker-Planck equation governing the transport of solar protons are obtained in three dimensions (time t, radial distance r, energy T) with the diffusion coefficient represented by κ = κ0rbTa. The October 4, 1968, solar flare particle event is re-examined, and the rise and decay of the proton flux profiles for > 10, ;30 and > 60 MeV particles can be reasonably well reproduced with an instantaneous injection and a distant (10 AU) free escape boundary. The best fit is achieved with a diffusion coefficient κ = 1.4 × 1020 r0.5 T0.75cm2sec where r is in AU and T in MeV.  相似文献   

11.
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 CH3+CH4+ = 1.5 ± 0.3. 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   

12.
Measurements of the emission intensities of the 557.7 nm line and Herzberg bands and of O(3P) concentrations carried out on two coordinated rocket flights at South Uist during the night of 8/9 September 1975 are presented. An examination of the 557.7 nm emission and O(3P) data on the basis of recent data on relevant rate coefficients has shown that the results can be interpreted on the basis of the Barth mechanism for the production of O(1S) atoms but not the Chapman mechanism. Evidence is provided that the A3Σ+u state of O2 could be responsible for the O(1S) production in the Barth mechanism. Values of the rate coefficients involved are deduced from a comparison of the 557.7 nm and Herzberg emission rates.  相似文献   

13.
Simultaneous measurements of the 6300 Å airglow intensity, the electron density profile, and F-region ion temperatures and vertical ion velocities taken at the Arecibo Observatory in March 1971 are utilized in the height integrated continuity equation to extract the number of photons'of 6300 Å emitted per recombination. After accounting for quenching of O(1D) and the electrons lost via NO+ recombination, the efficiency of O(1D) production by the dissociative recombination of O2+ is determined to be 0.6 ± 0.2 including cascading from the O(1S) state. The uncertainty includes both random measurement errors and estimates of possible systematic errors.  相似文献   

14.
Previous studies based on radio scintillation measurements of the atmosphere of Venus have identified two regions of small-scale temperature fluctuations located in the vicinity of 45 and 60 km. A global study of the fluctuations near 60 km, which are consistent with wind-shear-generated turbulence, was conducted using the Pioneer Venus measurements. The structure constants of refractive index fluctuations cn2 and temperature fluctuations cT2 increase poleward, peak near 70° latitude, and decrease over the pole; cn2 varies from 2 × 10?15 to 1.5 × 10?14m23 and cT2 from 4 × 10?3 to 7 × 10?2°K2m?23. These results indicate greater turbulent activity at the higher latitudes. In the region near 45 km the refractive index fluctuations and the corresponding temperature fluctuations are substantially lower. Based on the analysis of one representative occultation measurement, cn2 = 2 × 10?16m?23and cT2 = 7.3 × 10?4°K2m?23 in the 45-km region. The fluctuations in this region also appear to be consistent with wind-shear-generated turbulence. The turbulence level is considerably weaker than that at 60 km; the energy dissipation rate ε is 4.9 × 10?5m2sec?3 and the small-scale eddy diffusion coefficient K is 2 × 103 cm2 sec?1.  相似文献   

15.
16.
A major loss process for the metastable species, O+(2D), in the thermosphere is quenching by electrons
O+(2D) + e → O+(4S) + e
.To date no laboratory measurement exists for the rate coefficient of this reaction. Thermospheric models involving this process have thus depended on a theoretically calculated value for the rate coefficient and its variation with electron temperature. Earlier studies of the O+(2D) ion based on the Atmosphere Explorer data gathered near solar minimum, could not quantify this process. However, Atmosphere Explorer measurements made during 1978 exhibit electron densities that are significantly enhanced over those occurring in 1974, due to the large increases that have occurred in the solar extreme ultraviolet flux. Under such conditions, for altitudes ? 280 km, the electron quenching process becomes the major loss mechanism for O+(2D), and the chemistry of the N+2 ion, from which the O+(2D) density is deduced, simplifies to well determined processes. We are thus able to use the in situ satellite measurements made during 1978 to derive the electron quenching rate coefficient. The results confirm the absolute magnitude of the theoretical calculation of the rate coefficient, given by the analytical expression k(Te) = 7.8 × 10?8 (Te/300)?0.5cm3s?1. There is an indication of a stronger temperature dependence, but the agreement is within the error of measurement.  相似文献   

17.
Direct photolysis of O3 and quenching of O(1D) by N2 provide abundant sources of fast oxygen atoms for the Earth's lower atmosphere. The concentration of atoms with energy above 0.7 eV may exceed the concentration of O(1D) for all altitudes below 18 km and these atoms may play an important role in lower atmospheric chemistry. Distribution functions for O(3P) are given for the energy interval 0.1-1.3 eV, for a range of altitudes from 0 to 62 km.  相似文献   

18.
The photoionization of optically thin barium clouds is analyzed and shown to occur primarily by a two-step process involving the 3D metastable term as the ntermediate state. The equilibrium populations of the 1D and 3D metastable levels are calculated and found to differ significantly from the values now in the literature. These populations are combined with our newly available photoionization data to calculate the resulting photoionization rate in the upper atmosphere.  相似文献   

19.
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 X1 Σg+ ground state to a continuum level of the X2 Σg+ 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   

20.
Recent laboratory measurements of the deactivation rate constants for O(1S) have suggested that the dominant production mechanism for the green line in the nightglow is a two-step process. A similar mechanism involving energy transfer from an excited state of molecular oxygen is considered as a potential source of the OI (5577 Å) emission in the aurora. It is shown that the mechanism, O2 + e → O21 + e O21 + O → O2 + O(1S), is consistent with auroral observations; the intermediate excited state has been tentatively identified as the O2(c1?u) state. For the proposed energy transfer mechanism to be the primary source of the auroral green line, the peak electron impact cross-section for O21 production must be approximately 2 × 10?17 cm2.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号