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1.
Effects of ion excitation on charge transfer reactions of the Mars, Venus, and Earth ionospheres 总被引：1，自引：0，他引：1
The absolute reaction cross sections and reaction rate coefficients as a function of photoionisation energy for 25 ion-molecule reactions (charge transfer reactions except for one) have been measured between the most abundant species present as ions or neutral in the Mars, Venus and Earth ionospheres: O2, N2, NO, CO, Ar and CO2.This study shows the strong influence of electronic as well as vibrational internal energy on most ion-molecule reactions. In particular endothermic charge transfer reactions are driven by electronic excitation of O2+ and NO+ ions in their a4Πu and a3Σ+ metastable states, respectively. Moreover, it is shown that lifetimes of these metastable states are sufficient to survive the mean free path in the lowest part of ionospheres and therefore express their enhanced reactivity. The reactions of O2+ with NO as well as the reactions of CO2+ with NO, O2, CO and to a less extent N2 are driven by vibrational excitation. N2+ and CO+ reactions vary much less with photon energy than the other ones, except for the case of reactions with Ar. The effects of the molecular ion internal energy content on their reactivity must be included in the ionospheric models for most of the reactions investigated in the present work. It is also the case for the effect of collision energy on the CO++M reactions as we expect that a significant proportion of these CO+ could be produced with translational energy by dissociation of doubly charged CO22+, in particular in the Mars ionosphere. Recommended effective rate constant values are given as a function of VUV photon energy. 相似文献
2.
It is proposed that energy transfer from excited O2 contributes to the production of O(1S) in aurora. An analysis is presented of the OI5577 Å emission in an IBC II+ aurora between 90 and 130 km. The volume emission rate of the emission at these altitudes is consistent with the production rate of O(1S) by energy transfer to O(3P) from N2 in the A3Σ2+ state and O2 in the A3Σu+, C3Δc1Σu? states, the N2A state being populated by direct electron impact excitation and B → A cascade and the excited O2 states by direct excitation. Above the peak emission altitude (~105 km), energy transfer from N2A is the predominant production mechanism for O(1S). Below it, the contribution from quenching of the O2 states becomes significant. 相似文献
3.
Altitude distributions of electronically excited atoms and molecules of oxygen and nitrogen in the aurora have been obtained by means of rocket-borne wavelength scanning interference filter photometers launched from Fort Churchill, Manitoba (58.4°N, 94.1°W) on January 23, 1974. Atomic oxygen densities derived from mass spectrometer measurements obtained during the flight are used in conjunction with the volume emission rate ratio of the N2(C3Πu?B3Πg) (0-0) second positive and N2(A3Σu+, v = 1?X1Σg+) Vegard-Kaplan bands to derive a rate constant for quenching of the N2(A3Σu+, v = 1) level with O(3P) of 1.7(±0.8) × 10?11 cm3 s?1 These data, together with O den derived from the O2(b1Σg+) state nightglow emission observed during the rocket ascent, suggest that quenching of the N2(A3Σu+, v = 1) level by O2 has a significant positive temperature dependence. The processes involved in the production and loss of the N2(A3Σu+) state are considered and energy transfer from the N2(A3Σu+) state to O(3P) is found to be a significant source of the OI 5577 Å green line in this aurora at altitudes below 130 km. Emission from the NO(A2Σ+?X2Π) gamma bands was not detected, an observation which is consistent with the mass spectrometer data obtained during the flight indicating that the NO density was <108 cm3 at 110 km. On the basis of previous rocket and satellite measurements of the NO gamma bands, energy transfer from the N2(A3Σu+) state to NO(X2Π) is shown to be an insignificant source of the gamma bands in aurora. Altitude profiles of the N2(a1Πg?X1Σg+) Lyman-Birge-Hopfield band system are presented. 相似文献
4.
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
5.
A review is given of the stratospheric budgets of odd oxygen, odd nitrogen, nitrous oxide, methane and carbonyl sulfide. The stratospheric column production rate of NO by the reaction N2O + O(1D) → 2 NO is 1.1–1.9 × 108 molecules cm?2 s?1. The stratospheric loss rates for N2O, CH4 and COS are equal to 0.9–1.4 × 109, 1 × 1010 and 0.5 × 107 molecules cm?2 s?1, respectively. From currently available information on the global distributions of N2O and CH4 there are some indications of about two times smaller OH concentrations below 35 km than those which are calculated based on the latest compilation of kinetic data.Most significantly, however, it is shown that photochemical models and available ozone observations cannot be reconciled and that there may be particularly severe problems in the 25–35 km region. This issue is thoroughly discussed.Volcanic emissions of SO2 to the stratosphere may locally lead to much enhanced ozone concentrations and heating rates. These may influence the dynamic behaviour of volcanic plumes before their dispersion over large volumes of the stratosphere. 相似文献
6.
M.H. Rees 《Planetary and Space Science》1984,32(3):373-378
The results of recent laboratory experiments suggest that the reaction N+ + O2 → NO+ + O(1S) is the principal source of O(1S) in aurora. A negligible time delay between auroral ionization and O(1S) production is associated with this indirect process, which is a necessary condition for a viable mechanism. The volume emission rate ratio associated with this production source remains constant with altitude. The problems encountered by the currently accepted source of O(1S), the reaction of N2(A3Σ) molecules with atomic oxygen are explored, and the contributions of this and other reactions to the auroral green line emission are reevaluated. 相似文献
7.
A four-parameter model which assumes a Gaussian dependence of both temperature and pressure on distance from center is used to fit the compact part of coronal active regions as observed in X-ray photographs from a rocket experiment. The four parameters are the maximum temperature T M, the maximum pressure P M= 2NMkTM, the width of the pressure distribution σ P, and the width of the temperature distribution σ T = α1/2σP. The maximum temperature T M ranges from 2.2 to 2.8 × 106K, and the maximum density N M from 2 to 9 × 109cm?3. The range of σ P is from 2 to 4 × 109 cm and that of α from 2 to 7. 相似文献
8.
《Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science》2000,25(3):255-260
Recently, modelers have expressed a concern that the currently known chemistry of atmospheric NOy is deficient. It is therefore necessary to explore possible sources and sinks of atmospheric NOx that may have been overlooked. In this context, it is noteworthy that the experimentally observed, four-center, Woodward-Hoffman forbidden, reaction 02(B 3Σ) + N2 → NO(X) + NO (X) is atmospherically significant. In the 20 to 30 km region NOx production from this reaction may potentially exceed the production from the “classical” N20 + O(1D) reaction, and may provide a new mechanism to couple the solar UV variability and stratospheric ozone. The avoidance of the non-conservation of the orbital symmetry via the production of one NO in the excited electronic state being endothermic, it appears that the interaction of 02(B 3Σ) with the adjoining 1Λ, 3Λ and 3Σu+ states might be responsible for the reaction. Experimental studies of the reaction as a function of the vibrational levels of the B-state, temperature and pressure are needed for reliable atmospheric applications of this reaction. At altitudes greater than about 50 km the production of NO from 02(B) begins to decrease rapidly. The NO production from 02 (A 3Σ++) + N2 → NO + NO reaction may become important here, if the reaction is confirmed by experiments. These new sources of NOx call for new sinks of this species. In the upper stratosphere and mesosphere the chemical acceleration of NO dissociation via the reactions of electronically and vibrationally excited NO with 02 may help. In the lower atmosphere there is a possibility of the annihilation of NO, N02pair leading to the recreation of a stable NN bond. This might happen if N203 from NO and N02 recombination may photodissociate as N20 + 02. Unfortunately the requirements are stringent, and only experiments can tell whether or not this mechanism operates in the atmosphere. 相似文献
9.
A recent assessment by Rees (1984) of the contribution made to the excitation of O(1S) in the aurora by the reaction of N2(A3Σ+) with O(3P) is re-examined. It is demonstrated that the contribution attributed to this reaction may have been seriously under-estimated and it is shown that the results of recent laboratory investigations do not preclude this reaction as a major source of O(1s) in the aurora. 相似文献
10.
A theory of the i.r. radiation (2–20 μ) of the upper atmosphere (90–250 km height) has been developed. It includes the calculation of concentrations and temperatures as well as the analysis of atomic and molecular level population kinetics. Various excitation and quenching processes are analysed. Results are given for the following bands: NO (5.3μ), NO+(4.3μ.), CO (4.7 μ), N14N15 (4.4 μ), CO2(4.3 and 15 μ), H2O(2.7 and 6.3 μ), N2O(4.5; 7.8 and 17μ), O3(9.6 and 14.4 μ). The energy aspect of the problem is discussed. It is found that at a height of 120 km intensity in the region of 2 to 20 μ 3 to 10 is that of the 63 μ line of atomic oxygen. The comparison of theory with the experiment was carried out and satisfactory agreement obtained. The correlations of intensities in i.r. bands and emissions in visible and u.v. spectra were considered. 相似文献
11.
The height of the lower red border of type-B aurora has been determined by triangulation using TV cameras at two ground stations. A mean height of 91.4 ± 1.1 km was determined from a set of 12 measurements made under ideal conditions. A TV spectrograph was used simultaneously to seek possible spectral changes between 6400 and 6900 Å which would be indicative of changes in the vibrational distribution in the N2 First Positive bands. No significant difference was found in this distribution between the spectra from 93 and 122 km. The height distribution of contributions to the OI 5577 Å emission relative to the N+2 First Negative emission was modelled from 80 to 160 km. Contributions from electron impact on atomic O, O+2 dissociative recombination and N2(A)O energy transfer were included. Account was taken of recent laboratory data on O(1S) quenching. It was concluded that these processes could explain the excitation of O(1S) in normal aurora and the height distribution of OI 5577 Å in type-B red aurora. It was confirmed that the lifetime ofO(1S) in type-B red auroral rapid time variations is about 0.5 s and it was found from the model that the observed time variation can be reproduced by the mechanisms considered, provided the concentration of NO in the auroral atmosphere is about 1 × 109 at 95 km. Before reasonable certainty can be attained in the correctness of the interpretation it will however be necessary to have reliable simultaneous observations of neutral atmospheric composition particularly for O and NO as well as unchallengeable measurements of the yields of O(1S) for the processes considered and for several other processes which have been suggested recently. 相似文献
12.
N2 2P fluorescent intensity was monitored as a function of incident photon energy from 40 to 70 eV. A structure was seen near 52.2 eV. This feature is attributed to the scattering of photoelectrons originating from the N2 2σg molecular orbital with a binding energy of about 37.7 eV. The kinetic energy of these photoelectrons corresponds to the peak of the 2P excitation cross section at 14.5 eV. 相似文献
13.
The excitation mechanism for O2 Herzberg Bands as given by Young and Black (1966) is examined. It is found that O2 Herzberg Bands are heavily quenched by N atoms, while (0,0) and (0,1) Atmospheric Bands are quenched mainly by CO, NO, O2 and N2, NO, O2 respectively. The emission of Herzberg Bands is found to arise from two layers centred at 80 and 100 km. The rate coefficients of a number of quenching reactions involving atmospheric gases are obtained theoretically. 相似文献
14.
《Physics and Chemistry of the Earth, Part C: Solar, Terrestrial & Planetary Science》2001,26(7):527-532
The nitrogen isotope ratio of middle atmosphere nitrogen oxide is predicted as a function of altitude. Nitrogen oxides originate photochemically either from stratospheric nitrous oxide reacting with O(1D) or in the mesosphere and thermosphere from direct dissociation of N2 and ionization-initiated reactions involving O2 and N2. During its formation process, N2O acquires a nitrogen isotopic composition of N isotopes different than N2. Photodissociation within the stratosphere also modifies the proportion of isotopes. Reaction of stratospheric NO with O3 produces NO2, which when photodissociated yields NO depleted in 15N relative to NO2 in laboratory air. The value of δ15NO in the stratosphere is −100‰. In the altitude region between 50 and 65 km, NO is transformed into NO2 and then returned to NO by reaction of NO2 with O and by NO2 photodissociation. These reactions determine the isotopic makeup of NO. Above 65 km, nitric oxide is produced by local ionization processes and gas phase photochemical reactions involving N2 and excited O2. These processes determine the isotopic composition of NO in the upper mesosphere and thermosphere. Here δ15NO is 0‰. Air transported into the mesosphere above 65 km will reflect the NO isotopic values of the region below, while mesospheric NO transported below 65 km will not be distinguishable from NO originating in the stratosphere. 相似文献
15.
A model calculation to predict infrared Shuttle flow due to the radiative relaxation of vibration of the NO molecule is presented. Space Shuttles hit atmospheric NO molecules at a very high speed (≈ 8 km s?1) and excite vibrational and rotational motions up to the temperature of 54,000 K. With the electric dipole radiation of Δν = 1, 2, 3, and particularly 4 (ν is the vibrational quantum number), the excited NO molecules emit infrared radiation before they collide with other molecules. The total radiation power is estimated to be 170AμW, where A is the cross-section area of the Shuttle in m2 if no adsorption of the NO molecule takes place on the Shuttle surface. The intensity of each infrared line is calculated as a function of time, including all vibrational states up to ν = 35. For example, the 5039 cm?1 line (ν = 24 → 20) has a maximum intensity of about 2.3 × 10?21 W molecule at around 0.2 ms, which corresponds to 80 cm from the Shuttle surface if the recoil speed of the molecules is 4 km s?1. 相似文献
16.
Far-IR (25-50 μm, 200-400 cm−1) nadir and limb spectra measured during Cassini's four year prime mission by the Composite InfraRed Spectrometer (CIRS) instrument have been used to determine the abundances of cyanogen (C2N2), methylacetylene (C3H4), and diacetylene (C4H2) in Titan's stratosphere as a function of latitude. All three gases are enriched at northern latitudes, consistent with north polar subsidence. C4H2 abundances agree with those derived previously from mid-IR data, but C3H4 abundances are about 2 times lower, suggesting a vertical gradient or incorrect band intensities in the C3H4 spectroscopic data. For the first time C2N2 was detected at southern and equatorial latitudes with an average volume mixing ratio of 5.5±1.4×10−11 derived from limb data (>3-σ significance). This limb result is also corroborated by nadir data, which give a C2N2 volume mixing ratio of 6±3×10−11 (2-σ significance) or alternatively a 3-σ upper limit of 17×10−11. Comparing these figures with photochemical models suggests that galactic cosmic rays may be an important source of N2 dissociation in Titan's stratosphere. Like other nitriles (HCN, HC3N), C2N2 displays greater north polar relative enrichment than hydrocarbons with similar photochemical lifetimes, suggesting an additional loss mechanism for all three of Titan's main nitrile species. Previous studies have suggested that HCN requires an additional sink process such as incorporation into hazes. This study suggests that such a sink may also be required for Titan's other nitrile species. 相似文献
17.
V.A. Krasnopolsky 《Planetary and Space Science》1981,29(9):925-929
The excitation, energy transfer and quenching of O2 (A3 Σu+, C3 Δu, c1 Σu?) and O(1S) are discussed, taking into account laboratory measurements and observations on the airglow of the Earth, Venus and Mars. The excitation of O(1S) occurs by the Barth mechanism with O2(c) as a precursor: the rate coefficient is 2.5 × 10?12 cm3 s?1 for υ > 0 and 2.5 × 10?12 exp() cm3 s?1for υ = 0. The O2(c) can be formed directly by recombination or by O2(A) and O2(C) colliding with other molecules; the O2(c) yield through quenching of these states is about 0.3 in air and about 1.0 in carbon dioxide. The rate coefficients of some processes that control the molecular oxygen bands and the atomic oxygen green line are estimated. 相似文献
18.
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+ (), CO+ (first negative), CO (fourth positive), CO (Cameron), CO2+ (), 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
19.
D. A. Varshalovich A. V. Ivanchik P. Petitjean R. Srianand C. Ledoux 《Astronomy Letters》2001,27(11):683-685
Having analyzed the spectrum of the quasar PKS 1232+0.82 taken by Petitjean et al. (2000), we identified HD molecular lines in an absorption system at redshift z=2.3377. We estimated the column density of HD molecules in this system, N(HD) = (1?4) × 1014cm?2. The excitation temperature of the first rotational level J=1 relative to the ground state J=0 is T ex=70 ± 7 K. As far as we know, this is the first detection of HD molecules at high redshift. 相似文献