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1.
Advances in attacking the problem of radiative transfer in the near infrared (NIR) bands of CO2 and CO under nonlocal thermodynamic equilibrium (NLTE) conditions depend on the accuracy of taking into account the radiation processes and inelastic collisions of CO2 and CO molecules. The focus of the paper is to substantially improve the physical model of the problem and update the calculation method. It is the first time the surface albedo is introduced into the problem of the molecular emission under NLTE conditions. The values of the rate constants for inelastic molecular collisions and their temperature dependences have been radically updated. In some cases, since laboratory measurements of these constants are lacking, different versions are provided for them. The relative abundance of CO2 and CO isotopologues is based on the ratios of isotope abundances for the elements C and O obtained from the measurements in the atmosphere of Mars. The intensity of extraterrestrial solar NIR radiation is specified on the base of the high-accuracy ground-based measurements. In the method for calculating the populations of vibrational states, we pioneer in completely taking into account the overlapping of spectral lines in the NIR bands of CO2 and CO.  相似文献   

2.
This work reports theoretical infrared and electronic absorption spectra of formaldehyde and its ions in gas phase and H2O ice at different levels of theory. The vibrational frequencies from this work at B3LYP/6-311++G** level are in agreement with the experimental determinations. The gas phase dipole moment of neutral formaldehyde 2.4 D is in excellent agreement with the experimental value of 2.33 D. An influence of ice on vibrational frequencies of neutral formaldehyde molecule was obtained using Self Consistence Isodensity Polarizable Continuum Model (SCI-PCM) with dielectric constant 78.5. Significant shift in vibrational frequencies for neutral formaldehyde molecule when studied in H2O ice and upon ionization is observed. All the vibrational modes in cation and anion of formaldehyde in gas phase are red shifted than the corresponding modes in neutral formaldehyde. Two vibrational modes are blue shifted and all other modes are red shifted for neutral formaldehyde in H2O ice. Time dependent density functional theory (TDDFT) is used to study electronic absorption spectrum of neutral formaldehyde and its charged states. It is found that like neutral formaldehyde, its cation and anion also display strong σ→σ ∗ electronic transitions in vacuum and far UV regions. This study should help in detecting formaldehyde molecule and its ions in gas phase and in H2O ice in different astronomical environment.  相似文献   

3.
The estimates of the population of excited vibrational states of the CO2 molecule and of the rate of radiative cooling of the atmosphere in the 15-m CO2 band are given for the nighttime mesosphere and thermosphere of Mars. For the first time, these estimates are made (1) with allowance for the overlap of lines in the 15-m band; (2) for a wide set of vibrational states of seven isotopes of the CO2 molecule, which was used earlier in the solution of a similar terrestrial problem; and (3) using the rate constant for quenching of the CO2(0110) state in collisions with oxygen atoms, which has been recently measured for low temperatures by Khvorostovskaya et al. (2002). The main results are as follows. 1. The approximation of isolated lines provides a satisfactory accuracy of determining the radiative cooling rate and overestimates vibrational temperatures of the states of the 2 mode by no more than 3 K for the 12C16O2 molecule and by no more than 2 K for low-abundant isotopes of the CO2 molecule. 2. A reasonably high accuracy of estimating the cooling rate can be achieved by taking into account only fundamental vibrational transitions in 12C16O2, 13C16O2, 16O12C18O, and 16O12C17O molecules and the hot transitions 22 2 and 32 22 in the 12C16O2 molecule. 3. The vertical profile of the total rate of radiative cooling displays two peaks. The maximum near a height of 130 km is very sensitive to temperature and to the ratio of the mixture for oxygen in the atmosphere.  相似文献   

4.
Nonthermal emission which occurs in the cores of the 9.4- and 10.4-μm CO2 bands on Mars has been recently identified as a natural atmospheric laser. The emission is believed to be excited by absorption of near-ir solar flux, followed by collisional transfer to the 00°1 state of CO2. A numerical model based on this mechanism is developed which includes the solar pumping contributed by ～2 × 104 near-ir CO2 lines. The non-Local Thermodynamic Equilibrium (NLTE) radiative transfer problem is solved to obtain the 00°1 vibrational state population. This model successfully reproduces the existing center-to-limb observations, although higher spatial resolution observations are needed for a definitive test. The model also predicts total fluxes which are close to the observed values. The strength of the emission is predicted to be closely related to the instantaneous near-ir solar heating rate. Calculation of the CO2 level populations in this model supports the identification of this emission as a natural atmospheric laser. Both Mars and Venus are predicted to exhibit level inversions; at large zenith distances several percent of the emergent intensity will be due to stimulated emission. While the stimulated emission present in these lines is not large enough to be of importance to mesospheric radiative equilibrium, it has other interesting consequences. The construction of large-volume radiation-pumped lasers, which utilize CO2 planetary mesospheres as a gain medium, is theoretically possible.  相似文献   

5.
It is demonstrated that under conditions which approximate those of the Martian ionosphere traces of CO and O2 can be effectively incorporated in ion clusters via ion-molecule reaction schemes initiated by the CO2+ ion. For example, when 0.3 % CO is added to CO2, (CO)2+ and [(CO)2CO2]+ appear as the major cations (584 Å radiation, 300°K). In mixtures containing O2 in addition to CO2 (CO2. O2)+ and [(CO2)2O2]+ are important species. A recently proposed mechanism to account for the low abundance of CO and O2 in the Martian atmosphere is discussed in the light of these observations.  相似文献   

6.
This work presents model calculations of the diurnal airglow emissions from the OH Meinel bands and the O2 IR atmospheric band in the neutral atmosphere of Mars. A time-dependent photochemical model of the lower atmosphere below 80 km has been developed for this purpose. Special emphasis is placed on the nightglow emissions because of their potential to characterize the atomic oxygen profile in the 50-80 km region. Unlike on Earth, the OH Meinel emission rates are very sensitive to the details of the vibrational relaxation pathway. In the sudden death and collisional cascade limits, the maximum OH Meinel column intensities for emissions originating from a fixed upper vibrational level are calculated to be about 300 R, for transitions v′=9→v′?8, and 15,000 R, for transitions v′=1→v′=0, respectively. During the daytime the 1.27 μm emission from O2(), primarily formed from ozone photodissociation, is of the order of MegaRayleighs (MR). Due to the long radiative lifetime of O2(), a luminescent remnant of the dayglow extends to the dark side for about two hours. At night, excited molecular oxygen is expected to be produced through the three body reaction O + O + CO2. The column emission of this nighttime component of the airglow is estimated to amount to 25 kR. Both nightglow emissions, from the OH Meinel bands and the O2 IR atmospheric band, overlap in the 50-80 km region. Photodissociation of CO2 in the upper atmosphere and the subsequent transport of the atomic oxygen produced to the emitting layer are revealed as key factors in the nightglow emissions from these systems. The Mars 5 upper constraint for the product [H][O3] is revised on the basis of more recent values for the emission probabilities and collisional deactivation coefficients.  相似文献   

7.
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   

8.
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   

9.
A study of the CO2 atmospheric emissions at 10-μm in the upper atmospheres of Mars and Venus is performed in order to explain a number of ground-based measurements of these emissions recently taken at very high spectral resolution in both planets. The measurements are normally used to derive atmospheric temperatures and winds, but uncertainties on the actual emission layers were so far a serious drawback for their correct interpretation. The non-LTE models used for Mars and Venus in the present analysis are entirely similar in order to perform consistent comparisons between the two planets. In particular, the same scheme of CO2 states and ro-vibrational bands are used, with similar assumptions on collisional routes and rate coef?cients, and also the same radiative transfer approximations. The emissions at 10-μm are produced in both atmospheres by the same excitation mechanism: radiative pumping of the CO2(0001) vibrational state by direct solar absorption(at 4.3 μm) and indirect absorption (at 2.7 μm, followed by collisional quenching). The computed radiances are specially strong in the upper mesosphere and lower thermosphere of the two planets during maximum solar illumination, producing a population inversion in such conditions with the lower states of the bands, the CO2 (1000) and CO2(0200). We obtained that other population inversions are also possible, involving higher energy CO2 states. The larger solar ?ux available on Venus is found to produce larger vibrational populations and stronger emissions than equivalent atmospheric layers on Mars, in agreement with the observations. A number of perturbation studies were used to determine the exact emission altitudes, or weighting function peaks, for usual nadir sounding. The sensitivity of the emission to non-LTE model uncertainties and to atmospheric variations in temperature and CO2 density is also presented. The dependence with the solar zenith angle and with the emission angle, as obtained with this model, could also be useful for guiding future observations.  相似文献   

10.
We report on mid-resolution (R∼2000) spectroscopic observations of Titan, acquired in November 2000 with the Very Large Telescope and covering the range 4.75-5.07 μm. These observations provide a detailed characterization of the CO (1-0) vibrational band, clearly separating for the first time individual CO lines (P10 to P19 lines of 13CO). They indicate that the CO/N2 mixing ratio in Titan’s troposphere is 32±10 ppm. Comparison with photochemical models indicates that CO is not in a steady state in Titan’s atmosphere. The observations confirm that Titan’s 5-μm continuum geometric albedo is ∼0.06, and further indicates a ∼20% albedo decrease over 4.98-5.07 μm. Nonzero flux is detected at the 0.01 geometric albedo level in the saturated core of the 12CO (1-0) band, at 4.75-4.85 μm, providing evidence for backscattering on the stratospheric haze. Finally, emission lines are detected at 4.75-4.835 μm, coinciding in position with lines from the CO(1-0) and/or CO(2-1) bands. Matching them by thermal emission would require Titan’s stratosphere to be much warmer (by ∼ 25 K at 0.1 mbar) than indicated by the methane 7.7-μm emission and the Voyager radio-occultation. We show instead that a nonthermal mechanism, namely solar-excited fluorescence, is a more plausible source for these emissions. Improved observations and laboratory measurements on the vibrational-translational relaxation of CO are needed for further interpretation of these emissions in terms of a CO stratospheric mixing ratio.  相似文献   

11.
Shved  G. M.  Semenov  A. O. 《Solar System Research》2001,35(3):212-226
The standard problem of radiative transfer in a rovibrational band is formulated for an optically semi-infinite plane-parallel planetary atmosphere using a model of a linear molecule with two vibrational states. The solution of the problem describes the variation with height of the population of the excited vibrational state due to the existence of the upper boundary of the atmosphere. We seek this solution as a function of the specially introduced dimensionless parameters—the atmosphere depth and four similarity parameters—and study it for the parameter values that can be realized in the planetary atmospheres, including the atmospheres of extrasolar planets. It is shown that an increase in the optical density of the atmosphere can reduce the population of an excited vibrational state in the band at the upper boundary of the atmosphere by as much as several orders of magnitude as compared to the population corresponding to the optically thin band limit. The anomalous decrease in the opacity of the atmosphere, when only several lines of the band are involved in radiative transfer, is predicted. We also determined the accuracy of calculating the population in the approximation of the Doppler line profile. An approximate formula is obtained for the dimensionless height of the boundary of the layer in which the local thermodynamic equilibrium exists for vibrational states. We propose a model and the formula following from this model to roughly evaluate the decrease in this height due to the impact on the population of additional radiative transitions between the state being considered and the underlying state belonging to another vibrational mode of the molecule.  相似文献   

12.
The detection of CH4 in the martian atmosphere, at a mixing ratio of about 10 ppb, prompted Krasnopolsky et al. [Krasnopolsky, V.A., Maillard, J.P., Owen, T.C., 2004. Icarus 172, 537-547] and Krasnopolsky [Krasnopolsky, V.A., 2006. Icarus 180, 359-367] to propose that the CH4 is of biogenic origin. Bar-Nun and Dimitrov [Bar-Nun, A., Dimitrov, V., 2006. Icarus 181, 320-322] proposed that CH4 can be formed in the martian atmosphere by photolysis of H2O in the presence of CO. We based our arguments on a clear demonstration that CH4 is formed in our experiments, and on thermodynamic equilibrium calculations, which show that CH4 formation is favored even in the presence of oxygen at a mixing ratio 1.3×10−3, as observed on Mars. In the present comment, Krasnopolsky [Krasnopolsky, V.A., 2007. Icarus, in press (this issue)] presents his arguments against the suggestion of Bar-Nun and Dimitrov [Bar-Nun, A., Dimitrov, V., 2006. Icarus 181, 320-322], based on the effect of O2 on CH4 formation, the absence of kinetic pathways for CH4 formation and on the inadequacy of thermodynamic equilibrium calculations to describe the martian atmosphere. In this rebuttal we demonstrate that experiments with molecular oxygen at a ratio of O2/CO2=(8.9-17)×10−3, exceeding the martian ratio, still form CH4. Thermodynamic equilibrium calculations replicate the experimental CH4 mixing ratio to within a factor of 1.9 and demonstrate that CH4 production is favored in the martian atmosphere, which is obviously not in thermodynamic equilibrium. Consequently, we do not find the presence of methane to be a sign of biological activity on Mars.  相似文献   

13.
The calculation of number densities of CO2, H2O and N2 photolysis products was carried out for the Martian atmosphere at heights up to 60 km. The ozone distributed in the atmosphere as a layer of 10 km width with [O3] max = 2.5 × 109 cm3 at height of 35 km which agree well with the results of u.v. observations on the evening terminator from the Mars-5 satellite. The calculated densities of O2, CO and H2O are also in good agreement with the measured data. The eddy diffusion coefficient is equal to 3 × 106 in the troposphere (h ? 30 km) and 108 cm2 s?1 above 40 km. The dependence of the total ozone content on water vapour amount in the atmosphere is considered; the hypothesis about the influence of water ice aerosol on the ozone formation is proposed to explain the high concentrations of ozone in the morning.  相似文献   

14.
The model of the standard problem of radiative transfer in a vibrational–rotational band that we suggested previously (Shved and Semenov, 2001) for a nonlocal thermodynamic equilibrium (non-LTE) in vibrational molecular states is used to study the populations of these states in a nonisothermal planetary atmosphere. The temperature profile in the atmosphere is specified as a temperature perturbation in the form of a Gaussian function that is superimposed on an isothermal atmosphere. We show that the temperature profile has a complex effect on the state populations, which makes it difficult to analytically represent this effect. We investigate the influence of the peculiar features of the temperature profile in an LTE layer on the non-LTE height and suggest a criterion for determining those features that weakly affect this height. Using the populations of the CO2 0110 and 0001 states in the atmospheres of the Earth and Mars as examples, we show that the formulas suggested for estimating the non-LTE height are efficient.  相似文献   

15.
We report on PFS-MEX (Planetary Fourier Spectrometer on board Mars Express) limb observations of the non-Local Thermodynamic Equilibrium emission by CO and CO2 isotopic molecules. The CO emission is observed peaking at altitudes lower than the CO2 emission peak. Two orbits have been considered, which explore latitudes from 75 to 15° N, located in local time at 11:30 and 06:40, and with Ls=138° and 168°, respectively. In general in the season considered (northern summer) the emission intensity increases going to lower latitudes. The peak emission height is also decreasing with decreasing latitude. The CO2 isotopic molecules are emitting radiance out of proportion with respect to the normal isotopic abundance, which surely indicates a strong contribution from a large number of much weaker CO2 bands, a result that will demand careful theoretical modeling. By comparison with Hitran data base we can identify, among the emitting bands, the second hot band for the 626 and 636 molecule, while for the 628 and 627 emission from the third hot bands are very possible. Other minor bands or lines are also observed in emission for the first time in Mars. In one of the two orbits considered, the orbit 1234 of MEX, we also observe at altitudes 80-85 km scattered radiation, with indication of CO2 ice aerosols as scattering centers. At the same altitude the Pathfinder descending measurements show a temperature that allows CO2 condensation. Pathfinder measurements were at 03:00 local time, while our observations are for orbit 1234 showing CO2 ice signature at 11:30 local time. These non-LTE limb emissions, with their unprecedented spectral resolution in this portion of the near infrared and their sensitivity and geographical coverage, will represent in our opinion an excellent data set for testing current theoretical models of the martian upper atmosphere.  相似文献   

16.
Band models for CO2 and H2O absorption are described, and used to model the Venera 11 spectra near 1 μm. An effective-path approximation is used to allow for scattering in the clouds. The model has 10 layers and uses 211 CO2 and 15 H2O vibrational transitions, at 5 cm? resolution. Within a factor of 2, a maximum absorption in the 0.94-μm H2O band just below the clouds, corresponding to 200 ppm by volume, in agreement with V. I. Moroz, N. A. Parfen'ev, and N. F. San'ko (1979, Cosmic Res. 17, 601–614) is found. More accurate band strenghts are needed to model the bottom scale height accurately. The possibility that the 0.94-μm feature is blended with a band of some other molecule has been examined. Ten possible chemical species were examined, with negative results.  相似文献   

17.
W-H. IP  D.A. Mendis 《Icarus》1976,28(3):389-400
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18.
The main bands of the Schüler system of ND4 and NH4 have been observed at high resolution. On the basis of these spectra, Watson, in a separate paper, has analysed the ND4 main band showing that it represents a2F2 → 2 A1 transition of a tetrahedral molecule. The observed wavenumber data for both ND4 and NH4 are presented; the latter have not yet been analysed. Isotopic bands for15ND4,14ND3H,14ND2H2,14NDH3 have also been obtained and as previously pointed out confirm the assumed carrier of the spectrum. The much weaker bands accompanying the main Schüler band on the short and long wavelength sides are photographed at medium resolution. The interpretation of these bands in terms of the vibrational levels of upper and lower states is briefly discussed.  相似文献   

19.
In absence of other mechanisms, the main input of CO2into the Venusian atmosphere is via volcanic out gassing. Since Venus can be regarded as a planet-wide large igneous province, we can expect large quantities of CO2 being transferred into its atmosphere via volcanic out gassing. We have quantified the maximum possible amount of CO2 that can be out gassed via a single massive episode of resurfacing of the planet. This figure (5.6 × 1019 kg of CO2) is about 8 times smaller than the total CO2 present in the Venusian atmosphere (4.55 × 1020 kg CO2). The lack of planet-wide, efficient mechanisms for the recycling of CO2 on Venus indicates that CO2 has progressively accumulated in the atmosphere. Based on these considerations we suggest that the “equivalent” to eight global resurfacing episodes would be required to account for the present values of CO2 atmosphere. This revised version was published online in July 2006 with corrections to the Cover Date.  相似文献   

20.
The influence of hydrogen sulfide, a still-undetected key molecule for the Jovian atmospheric chemistry in the infrared spectrum, was investigated. Synthetic spectra including various vertical distribution profiles of H2S have been computed and compared with observational data for Jupiter in the 2- to 15-cm?1 and 1160- to 1200-cm?1 spectral ranges. No firm conclusion about the presence of H2S can be drawn from the latter spectral region because of large uncertainties in gaseous opacities. In the microwave range, H2S is found to be a possible candidate to explain the measurements. Constraints to its vertical distribution which would imply a significant supersaturation in the troposphere are derived. Physical and chemical processes involving H2S in the atmosphere are discussed in the light of this hypothesis.  相似文献   

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