Hot Oxygen Atoms Research Articles

Hot oxygen corona at Europa

A model of the hot oxygen exosphere at Europa was constructed. The source term for the hot atoms was assumed to be dissociative recombination of O2+ and Liouville's theorem was used to calculate their altitude distribution. It was found that near the surface the hot oxygen density is in excess of 200 cm−3, dropping to a value on the order of 50 cm−3 at 1500 km. These calculations indicate that the hot atomic oxygen densities are considerably less than the thermal molecular oxygen ones, but slightly larger than the measured sodium values. The escape flux of the hot oxygen atoms was calculated to be on the order of 1.4×108 atoms cm−2 sec−1. This corresponds to a global escape rate of 4.4×1025 atoms sec−1, which is more than an order of magnitude less than the estimated atmospheric sputtering rate.

Slowing of energetic O(3P) atoms in collisions with N2

Energetic atoms influence the composition, the thermal structure and the evolution of the upper atmosphere. We investigate the slowing of energetic O(3P) atoms by elastic and inelastic collisions with N2. Results of quantum mechanical and semiclassical calculations of energy and angle‐resolved cross sections are presented for elastic and inelastic collision of O(3P) with N2. A general analytical expression is developed for the kernel of the Boltzmann equation for the energy distribution function which is valid for elastic and inelastic collisions and incorporates both the angle and the energy dependence of the cross sections. The Boltzmann kernel for the energy relaxation of fast O(3P) atoms is evaluated using the computed cross sections. We report values of the collision frequency, the average energy loss in elastic and inelastic collisions with N2, and the mean time and the number of collisions required to thermalize initially energetic O(3P) atoms. We compare the efficiencies of elastic and inelastic collisions in slowing down fast O(3P) atoms. These data are basic to the development of a reliable model of the atmospheric effects of the hot oxygen atoms produced by dissociative recombination, collisional quenching, photodissociation and photoelectron impact dissociation.

Hot-atom mechanism in photodesorption of molecular oxygen from a stepped platinum (113) surface

The photodesorption of oxygen admolecules was studied on a stepped Pt(113)=(s)2(111)×(001) surface with 193 nm irradiation at 110 K. Multidirectional desorptions were found to collimate at ±12–20° and ±45–49° off the surface normal and also along the surface normal in a plane along the trough. The first component is always dominant, and the weak second component only appears at higher oxygen coverages. The normally directed desorption is not significant. The translational energy of desorbing O2 peaks around 15–20° and 50°, confirming the inclined desorptions. It is proposed that these inclined components are due to the desorption induced by the impact of oxygen admolecules with hot oxygen atoms from the photodissociation of adsorbed molecular oxygen, emitted along the trough. A simple cosine distribution was found to fit the thermal desorption from oxygen admolecules and also the recombinative desorption of oxygen adatoms. The 193 nm irradiation also produces additional, less tightly bound oxygen adatoms, which yield a desorption component collimated at 15° from the surface normal in the step-down direction.

The effect of reagent translational energy on the dynamics of the reaction O(3P)+CS(X 1Σ+)→CO(X 1Σ+)+S(3P)

Two different regimes of collision energy are used to explore the role of additional translational energy on the dynamics of the reaction O(3P)+CS(X 1Σ+)→CO(X 1Σ+)+S(3P). Product CO rotational quantum-state population distributions for CO(v′=12, 13, and 14) are used as an indicator of the reaction dynamics, and these rotational distributions are presented for reaction of thermal reagents (at 298 K) and for translationally hot oxygen atoms formed by the 355 nm photolysis of NO2. The experimental measurements are compared with the results of quasiclassical trajectory calculations performed on an empirical London–Eyring–Polanyi–Sato potential energy surface tailored to model the observed dynamics for thermal reagents. Efficient conversion of the extra translational energy into product rotation is seen for all vibrational levels studied. The data are found to fit a simple model in which the fraction of the extra kinetic energy which appears as product rotation varies linearly with kinetic energy, and becomes unity for the fastest oxygen atoms produced by photolysis. The experimental results are interpreted in terms of an increasingly bent transition state for the reaction at higher collision energies, with the possibility of reagent reorientation towards a more linear transition state as the kinetic energy is decreased.

An aligned oxidation of carbon monoxide induced by 193 nm irradiation on platinum(113)

The angular and velocity distributions of desorbing CO 2 product were studied in the photoinduced CO oxidation on a stepped platinum(113) surface. The CO 2 desorption is sharply collimated into directions at ±23° from the bulk surface normal in a plane along the surface troughs. The velocity distribution analysis yields two desorption components with different translational temperatures. One has a high translational energy maximized around ±35° and the other an energy peaked at the surface normal. The surface parallel momentum of hot oxygen atoms is partly retained in the former desorption event.

Hot oxygen atom ballistics on Pt(111): collisional desorption of noble gases

Abstract Hot oxygen atoms formed by ultraviolet photofragmentation of chemisorbed O 2 on Pt(111) at T s =20 K induced collisional desorption of coadsorbed noble gases. Angular distributions of desorbing Ar, Kr, and Xe were sharply peaked at ∼35° from the surface normal. Mean translational energies of the noble gases were in the 0.12 eV (1400 K) range. The O atom photofragments were found to chatter between the surface and the noble gases during the desorption process. The fastest O atom photofragments produced at 250 nm had an energy of at least 0.73 eV.

New sources for the hot oxygen geocorona: Solar cycle, seasonal, latitudinal, and diurnal variations

This paper demonstrates the variability of thermospheric sources of hot oxygen atoms. Numerical calculations were performed for day and night, high and low solar activity, summer and winter, and low‐ and middle‐latitude conditions. Under most conditions, reactions involving metastable species are more important hot O sources than previously considered dissociative recombination of O2+ and NO+. All the hot O sources are an order of magnitude lower at midnight than at noon. At night, dissociative recombination of O2+ and NO+ are the most important sources. Quenching of vibrationally excited N2 (N2*) by O is the most important metastable source at night. Above 300 km, hot O sources increase by an order of magnitude between solar minimum and solar maximum. For a given level of solar activity, the high‐altitude total production rate of hot O kinetic energy is greater during winter than during summer, indicating a dominance of cooler hot O sources during summer. The N2* source dominates at low altitudes. At high altitudes it is almost negligible at solar minimum, but increases to become the dominant source at solar maximum. Atomic oxygen quenching of N(²D) is a large source at solar minimum and is still important at solar maximum. Overall, seasonal variations are small compared to solar cycle, diurnal and latitudinal variations. While quenching of metastable species is more important at midlatitudes than at low latitudes, there is little latitudinal variation in hot O production due to dissociative recombination of NO+ and O2+.

A kinetic model of the formation of the hot oxygen geocorona: 2. Influence of O+ion precipitation

A model of the oxygen geocorona near the exobase solving the nonlinear Boltzmann equation with a Monte Carlo method is used to calculate the distribution of the hot oxygen atoms during geomagnetically disturbed nighttime conditions. The precipitation of energetic O+ions and the subsequent enhancement of the hot O corona at high latitudes is simulated for the September 17, 1971, storm conditions. It is found that in such circumstances, the O+precipitation is a significant source of superthermal O atoms leading to important perturbations of the velocity distribution of the bulk oxygen population. The effective gas temperature near the exobase is similar to that in the undisturbed atmosphere, but the hot O density rises considerably over the quiet condition values.

The importance of new chemical sources for the hot oxygen geocorona

Exothermic reactions involving metastable neutrals and ions were recently proposed as sources of hot oxygen atoms in addition to the classical O2+ and NO+ dissociative recombination. The Boltzmann equations for thermal and nonthermal populations of O atoms are solved with a Monte Carlo stochastic simulation method. It is shown that the calculated energy distribution functions of O atoms are significantly in nonequilibrium in the transition region between the thermosphere and the exosphere. It is found that the inclusion of additional sources leads to stronger disturbances of the energy distribution function and, as a consequence, increases the nonthermal fraction of hot O atoms. The variation of the vertical distribution of hot O between solar maximum and minimum conditions is also evaluated and shows good agreement with the available experimental evidence.

A kinetic model of the formation of the hot oxygen geocorona: 1. Quiet geomagnetic conditions

A model of the hot oxygen geocorona in the transition region near the exobase is described. It is based on a Monte Carlo solution of the nonlinear Boltzmann equation for hot oxygen atoms produced by chemical processes usually considered as a source of hot oxygen (photodissociation of O2 and dissociative recombination of O2+ and NO+ ions). The evolution of the system is described stochastically as a series of random Markovian processes. The energy distribution function of the thermal and non‐thermal O(³P) atoms and of the nonthermal O(¹D) atoms is calculated from the thermospheric collision‐dominated region to the exosphere where the gas flow is virtually collisionless. The model is applied to equatorial latitudes for conditions of low solar and geomagnetic activity. Numerical simulations show that the distribution function of thermal oxygen is increasingly perturbed by collisions with the hot oxygen population at high altitudes and departs significantly from a Maxwellian distribution at all altitudes. The number density and temperature of the nonthermal oxygen atoms are derived from their microscopic distribution function and found to be in qualitative agreement with previous theoretical and experimental estimates.

First Measurement of Helium on Mars: Implications for the Problem of Radiogenic Gases on the Terrestrial Planets

108 ± 11 photons of the martian He 584-Å airglow detected by the Extreme Ultraviolet Explorer satellite during a 2-day exposure (January 22-23, 1993) correspond to the effective disk average intensity of 43 ± 10 Rayleigh. Radiative transfer calculations, using a model atmosphere appropriate to the conditions of the observation and having an exospheric temperature of 210 ± 20 K, result in a He mixing ratio of 1.1 ± 0.4 ppm in the lower atmosphere. Nonthermal escape of helium is due to electron impact ionization and pickup of He+ by the solar wind, to collisions with hot oxygen atoms, and to charge exchange with molecular species with corresponding column loss rates of 1.4 × 105, 3 × 104, and 7 × 103 cm-2 sec-1, respectively. The lifetime of helium on Mars is 5 × 104 years. The He outgassing rate, coupled with the 40Ar atmospheric abundance and with the K:U:Th ratio measured in the surface rocks, is used as input to a single two-reservoir degassing model which is applied to Mars and then to Venus. A similar model with known abundances of K, U, and Th is applied to Earth. The models for Earth and Mars presume loss of all argon accumulated in the atmospheres during the first billion years by large-scale meteorite and planetesimal impacts. The models show that the degassing coefficients for all three planets may be approximated by function δ = δ0(t0/t)1/2 with δ0 = 0.1, 0.04, and 0.0125 Byr-1 for Earth, Venus, and Mars, respectively. After a R2 correction this means that outgassing processes on Venus and Mars are weaker than on Earth by factors of 3 and 30, respectively. Mass ratios of U and Th are almost the same for all three planets, while potassium is depleted by a factor of 2 in Venus and Mars. Mass ratios of helium and argon are close to 5 × 10-9 and 2 × 10-8 g/g in the interiors of all three planets. The implications of these results are discussed.

Sounding rocket observation of a hot atomic oxygen geocorona

A sounding rocket measurement of the ultraviolet, atomic oxygen dayglow reveals an excess of emission compared to standard thermospheric model calculations at exospheric altitudes. We explore two explanations for this discrepancy: a breakdown of the radiative transfer model due to nonlocal thermal equilibrium (non‐LTE) conditions above the exobase and a hot atomic oxygen geocorona. In particular, the effects of non‐LTE on the ³P2,1,0 sublevel populations are modeled, and a hot O component in the upper thermosphere and lower exosphere is added to investigate the effects on the modeled emissions. For both cases, the data are reanalyzed and compared with the results using a standard LTE model. A hot O geocorona having a peak density of 106 cm−3 at 550 km and a temperature of 4000 K is consistent with the data and appears to be the most reasonable explanation of the high‐altitude enhanced emissions observed in the data.

Helium in the Martian atmosphere

A simple two‐reservoir degassing model for the Earth decribes rather well the current degassing rate of 4He which is equal to (3±1)×106 cm −2s−1 according to data for the helium polar wind and the measured 3He/4He ratio. This value of the helium degassing and loss rate provides an important constraint in modeling of noble gases, and some recent models do not fit this constraint. Scaling this value to the known amounts of 40Ar in the atmospheres of Mars and the Earth and to U/K ratios in their surface rocks, this results in a crude estimate of the helium degassing rate on Mars, which is equal to 2.2×105 cm−2 s−1. Nonthermal escape of He is calculated using the daytime mean atmospheric models for low, mean, and high solar activity with He mixing ratio ƒHe = 1 ppm. Three processes contribute to He escape: (1) electron impact ionization and photoionization above the ionopause followed by solar wind sweeping away of the ions formed (1.3×105 cm−2s−1), (2) collisions with hot oxygen atoms formed mainly by recombination of O2+ (2.8×104 cm−2s−1), (3) charge exchange of He+ and CO2, N2, and CO between the exobase and ionopause (6×103 cm−2s−1). The derived mixing ratio for He is ƒHe = 1.4 ppm for the adopted degassing rate. The He 584 Å airglow intensity is equal to 37 R and 67 R at low and high solar activity, respectively. The intensities are 105 R and 240 R for ƒHe = 7 ppm, and 10 R and 16 R for ƒHe = 0.3 ppm. These brightnesses should be detectable using the Extreme Ultraviolet Explorer satellite. The measurement of helium on Mars is important for the determination of the planetary abundance of U and Th, element differentiation in the primordial nebula (by comparison with the Earth and Venus) and in the interior of Mars (by comparison with the U and Th fraction in the surface rocks on Mars measured by the Mars 5 and Phobos orbiters). This measurement makes possible an estimate of the radiogenic heat flux which is important for the thermal balance of Mars' interior.

Comment on “Ionospheric evidence of hot oxygen in the upper atmosphere of Venus”

The conclusion of Mahajan et al. (1992) that 'the existence of O(+) as dominant at (Venusian) ionopause altitudes in excess of 500-1000 km can only be explained if atomic oxygen is the major neutral constituent' is argued to be incorrect. It is suggested that at a transition region of about 200 km, thermal atomic oxygen is the dominant neutral gas, and hot oxygen is a minor species; thus the O(+) to H(+) ratio at high altitudes is not an indicator of the presence of hot oxygen at these altitudes. A 1D model for H(+) and O(+) appropriate for the dayside ionosphere of Venus shows that within hot atomic oxygen density values from 1000 to 10 exp 6/ cu cm at 150 km, the calculated H(+) and O(+) densities did not change in any meaningful way, because the hot oxygen population remained a minor neutral constituent below 200 km, which is the approximate height of the transition between chemical and diffusive equilibrium conditions for the ions.

Neutral particle environment of Mars: The exosphere-plasma interaction effects

Because of the non-existent or very weak intrinsic planetary magnetic field, the solar wind interaction process at Mars is characterized by direct streaming of the solar wind plasma flow through the Martian exosphere. Also as a result of the low gravity at Mars, rather extended distributions of hot oxygen atoms and cold hydrogen atoms could be found even at altitudes of a few thousand km. The ionization and subsequent pickup of such exospheric ions by the interplanetary electric field could have very important consequences on the structure of the bow shock, the injection of planetary heavy ions into the magnetospheric environment, and non-thermal mass loss. The hydrogen component of the exosphere might play a particularly important role in creating a seed population of reflecting ions as well as depleting the solar wind plasma - via charge exchange process - near the magnetopause.

Reactions involving hot oxygen (3P) atoms and isomeric 2-butene

ADVERTISEMENT RETURN TO ISSUEPREVArticleNEXTReactions involving hot oxygen (3P) atoms and isomeric 2-buteneRichard A. Ferrieri and Alfred P. WolfCite this: J. Phys. Chem. 1992, 96, 12, 4747–4752Publication Date (Print):June 1, 1992Publication History Published online1 May 2002Published inissue 1 June 1992https://doi.org/10.1021/j100191a006RIGHTS & PERMISSIONSArticle Views33Altmetric-Citations2LEARN ABOUT THESE METRICSArticle Views are the COUNTER-compliant sum of full text article downloads since November 2008 (both PDF and HTML) across all institutions and individuals. These metrics are regularly updated to reflect usage leading up to the last few days.Citations are the number of other articles citing this article, calculated by Crossref and updated daily. Find more information about Crossref citation counts.The Altmetric Attention Score is a quantitative measure of the attention that a research article has received online. Clicking on the donut icon will load a page at altmetric.com with additional details about the score and the social media presence for the given article. Find more information on the Altmetric Attention Score and how the score is calculated. Share Add toView InAdd Full Text with ReferenceAdd Description ExportRISCitationCitation and abstractCitation and referencesMore Options Share onFacebookTwitterWechatLinked InReddit PDF (782 KB) Get e-Alerts

The fast atomic oxygen corona extent of Mars

The production of fast oxygen atoms in the Martian exosphere as a result of the electron dissociative recombination of ions is re‐evaluated for the time period appropriate to the Phobos 2 mission. Because of the prevalent condition of solar maximum activities in 1989, both the upper atmosphere and ionsphere should have more extended structures than those encountered during the Viking Orbiter (VO) mission in 1976 which was near solar minimum. We compare the distributions of the hot oxygen atoms for these different levels of solar activities and find that the number density of the hot oxygen atoms during the Phobos 2 mission should be a factor of two larger than estimated for the time period of the VO mission. The non‐thermal escape rate of the exospheric oxygen atoms is thus comparable to the ionospheric escape rate measured in the Martian magnetotail. Furthermore, the flux of the oxygen ions picked up in the hot atomic corona should be more intense than previously thought.

Temperatures of individual ion species and heating due to charge exchange in the ionosphere of Venus

The coupled electron and multispecies ion energy equations were solved for daytime conditions in the Venus ionosphere. The heating rates due to charge exchange between hot oxygen atoms and thermal oxygen ions were calculated and incorporated into the energy equations. The combination of the traditional EUV heating and this hot oxygen energy source leads to calculated electron and individual ion temperatures significantly lower than the measured values during solar cycle maximum conditions. Calculations were also carried out for solar cycle minimum conditions, which led to considerably lower temperatures; no data are available which would allow direct comparisons of these results with measurements. In order to obtain calculated temperature values consistent with the observed ones, for solar cycle maximum conditions, topside heat inflows into the ion and electron gases have to be introduced or the thermal conductivity must be reduced by considering the effect of steady and fluctuating magnetic fields, as was done in previous studies. The addition of hot oxygen heating leads to minor increases in the calculated ion temperatures except for the case of reduced thermal conductivities. Separate temperatures were calculated for each ion species for a number of different conditions and in general the differences were found to be relatively small.

On the dust/gas tori of Phobos and Deimos

The dust and gas environment in the vicinity of the orbit of the Phobos moon is assessed using both theoretical methods and observations from previous missions to Mars. It is found that a stable ring of dust particles with radii ≈ 100 μm could exist with a normal optical depth close to the upper limit determined from the Viking Orbiter 1 mission. The presence of a gas ring with neutral number density substantially higher than the hot atomic oxygen background is possible only if the Phobos moon maintains a certain level of outgassing with Qgas > 1023 molec. s−l. The narrow width (≈ 400 km) and the strong plasma perturbations sometimes observed by the Phobos 2 spacecraft at crossings of the orbit of the Phobos moon are still a puzzle to be investigated by further data analysis.

Hot oxygen atoms in the upper atmospheres of Venus and Mars

The altitude distribution of the hot oxygen density was calculated for the upper atmospheres of Venus and Mars for solar cycle maximum and minimum conditions, respectively. The calculated values for Venus are in good agreement with the observed values and are about a factor of twenty larger than the calculated values for Mars at the exobase.