Doubly-charged ions in the planetary ionospheres: a review

This paper presents a review of the current knowledge on the doubly-charged atomic and molecular positive ions in the planetary atmospheres of the Solar System. It is focused on the terrestrial planets which have a dense atmosphere of N(2) or CO(2), i.e. Venus, the Earth and Mars, but also includes Titan, the largest satellite of Saturn, which has a dense atmosphere composed mainly of N(2) and a few percent of methane. Given the composition of these neutral atmospheres, the following species are considered: C(++), N(++), O(++), CH(4)(++), CO(++), N(2)(++), NO(++), O(2)(++), Ar(++) and CO(2)(++). We first discuss the status of their detection in the atmospheres of planets. Then, we provide a comprehensive review of their complex and original photochemistry, production and loss processes. Synthesis tables are provided for those ions, while a discussion on individual species is also provided. Methods for detecting doubly-charged ions in planetary atmospheres are presented, namely with mass-spectrometry, remote sensing and fine plasma density measurements. A section covers some original applications, like the possible effect of the presence of doubly-charged ions on the escape of an atmosphere, which is a key topic of ongoing planetary exploration, related to the evolution of a planet. The results of models, displayed in a comparative way for Venus, Earth, Mars and Titan, are discussed, as they can predict the presence of doubly-charged ions and will certainly trigger new investigations. Finally we give our view concerning next steps, challenges and needs for future studies, hoping that new scientific results will be achieved in the coming years and feed the necessary interdisciplinary exchanges amongst different scientific communities.     

A statistical mechanics description of environmental variability in metabolic networks

Many of the chemical reactions that take place within a living cell are irreversible. Due to evolutionary pressures, the number of allowable reactions within these systems are highly constrained and thus the resulting metabolic networks display considerable asymmetry. In this paper, we explore possible evolutionary factors pertaining to the reduced symmetry observed in these networks, and demonstrate the important role environmental variability plays in shaping their structural organization. Interpreting the returnability index as an equilibrium constant for a reaction network in equilibrium with a hypothetical reference system, enables us to quantify the extent to which a metabolic network is in disequilibrium. Further, by introducing a new directed centrality measure via an extension of the subgraph centrality metric to directed networks, we are able to characterise individual metabolites by their participation within metabolic pathways. To demonstrate these ideas, we study 116 metabolic networks of bacteria. In particular, we find that the equilibrium constant for the metabolic networks decreases significantly in-line with variability in bacterial habitats, supporting the view that environmental variability promotes disequilibrium within these biochemical reaction systems.     

CO2对790nm附近水线的压力加宽和位移

采用高灵敏的激光光腔衰荡光谱技术研究了CO2对160水分子v^2＋3v^3振动带跃迁线的压力诱导效应．为了抑制水的自碰撞效应,水的压力在实验中低于0．5Torr．基于铷原子吸收线和超稳法布里-珀罗标准确定了跃迁谱线高达10^-5cm^-1精度的绝对频率．采用软碰撞模型对吸收线进行模拟,获得了对应的线形参数．     

Laboratory studies of photochemistry and gas phase radical reaction kinetics relevant to planetary atmospheres

This review seeks to bring together a selection of recent laboratory work on gas phase photochemistry, kinetics and reaction dynamics of radical species relevant to the understanding of planetary atmospheres other than that of Earth. A majority of work focuses on the rich organic chemistry associated with photochemically initiated reactions in the upper atmospheres of the giant planets. Reactions relevant to Titan, the largest moon of Saturn and with a nitrogen/methane dominated atmosphere, have also received much focus due to potential to explain the chemistry of Earth's prebiotic atmosphere. Analogies are drawn between the approaches of terrestrial and non-terrestrial atmospheric chemistry.     

Photoinduced mechanism of formation and growth of polycyclic aromatic hydrocarbons in low-temperature environments via successive ethynyl radical additions

A novel ethynyl addition mechanism (EAM) has been established computationally as a practicable alternative to high-temperature hydrogen-abstraction-C2H2-addition (HACA) sequences to form polycyclic aromatic hydrocarbon (PAH) -like species under low-temperature conditions in the interstellar medium and in hydrocarbon-rich atmospheres of planets and their moons. Initiated by an addition of the ethynyl radical (C2H) to the ortho-carbon atom of the phenylacetylene (C6H5C2H) molecule, the reactive intermediate loses rapidly a hydrogen atom, forming 1,2-diethynylbenzene. The latter can react with a second ethynyl molecule via addition to a carbon atom of one of the ethynyl side chains. A consecutive ring closure of the intermediate leads to an ethynyl-substituted naphthalene core. Under single-collision conditions as present in the interstellar medium, this core loses a hydrogen atom to form ethynyl-substituted 1,2-didehydronaphthalene. However, under higher pressures as present, for example, in the atmosphere of Saturn's moon Titan, three-body reactions can lead to a stabilization of this naphthalene-core intermediate. We anticipate this mechanism to be of great importance to form PAH-like structures in the interstellar medium and also in hydrocarbon-rich, low-temperature atmospheres of planets and their moons such as Titan. If the final ethynyl addition to 1,2-diethynylbenzene is substituted by a barrierless addition of a cyano (CN) radical, this newly proposed mechanism can even lead to the formation of cyano-substituted naphthalene cores in the interstellar medium and in planetary atmospheres.     

Mass spectrometry in the U.S. space program: Past, present, and future

Recent years have witnessed significant progress on the miniaturization of mass spectrometers for a variety of field applications. This article describes the development and application of mass spectrometry (MS) instrumentation to support of goals of the U.S. space program. Its main focus is on the two most common space-related applications of MS: studying the composition of planetary atmospheres and monitoring air quality on manned space missions. Both sets of applications present special requirements in terms of analytical performance (sensitivity, selectivity, speed, etc.), logistical considerations (space, weight, and power requirements), and deployment in perhaps the harshest of all possible environments (space). The MS instruments deployed on the Pioneer Venus and Mars Viking Lander missions are reviewed for the purposes of illustrating the unique features of the sample introduction systems, mass analyzers, and vacuum systems, and for presenting their specifications which are impressive even by today's standards. The various approaches for monitoring volatile organic compounds (VOCs) in cabin atmospheres are also reviewed. In the past, ground-based GC/MS instruments have been used to identify and quantify VOCs in archival samples collected during the Mercury, Apollo, Skylab, Space Shuttle, and Mir missions. Some of the data from the more recent missions are provided to illustrate the composition data obtained and to underscore the need for instrumentation to perform such monitoring in situ. Lastly, the development of two emerging technologies, Direct Sampling Ion Trap Mass Spectrometry (DSITMS) and GC/Ion Mobility Spectrometry (GC/IMS), will be discussed to illustrate their potential utility for future missions.     

Vibrational quenching of CO2(010) by collisions with O(3P) at thermal energies: a quantum-mechanical study

The CO(2)(010)-O((3)P) vibrational energy transfer (VET) efficiency is a key input to aeronomical models of the energy budget of the upper atmospheres of Earth, Venus, and Mars. This work addresses the physical mechanisms responsible for the high efficiency of the VET process at the thermal energies existing in the terrestrial upper atmosphere (150 K相似文献   

Gas chromatography in space.

Gas chromatography has proven to be a very useful analytical technique for in situ analysis of extraterrestrial environments as demonstrated by its successful operation on spacecraft missions to Mars and Venus. The technique is also one of the six scientific instruments aboard the Huygens probe to explore Titan's atmosphere and surface. A review of gas chromatography in previous space missions and some recent developments in the current environment of fiscal constraints and payload size limitations are presented.     

Identification of the D(3h) isomer of carbon trioxide (CO3) and its implications for atmospheric chemistry.

The CO3 molecule is considered an important reaction intermediate in the atmospheres of Earth and Mars for quenching electronically excited oxygen atoms and in contributing to the anomalous 18O isotope enrichment. The geometry of the CO3 intermediate plays an important role in explaining these effects; however, only the cyclic (C(2v)) isomer has been experimentally confirmed so far. Here, we report on the first spectroscopic detection of the acyclic (D(3h)) isomer of carbon trioxide (12C16O3) via its nu1 and nu2 vibrational modes centered around 1165 cm(-1) under matrix isolation conditions; the identification of the 12C18O3, 13C16O3, 13C18O3, 16O12C18O2, and 18O12C16O2 isotopomers of the acyclic isomer confirms the assignments.     

Chemistry of HCNH+: mechanisms, structures, and relevance to Titan’s atmosphere

The chemistry of HCNH⁺ in Titan’s atmosphere is not completely understood despite previous experimental and theoretical studies. In response to recent suggestions in the literature, we have searched for specific products of the reactions of HCNH⁺ with H₂, CH₄, C₂H₂, and C₂H₄ using the flowing afterglow-selected ion flow tube technique. We have probed for an association mechanism for reaction with H₂, and associative-H₂ loss for the reactions involving CH₄, C₂H₂, and C₂H₄. In all cases, these reaction mechanisms were found to be inefficient pathways for the depletion of HCNH⁺. Our ab initio computational studies characterize the structures and energies for these mechanisms and indicate that the proposed pathways are endothermic or possess reaction barriers. We compare our studies to previous experimental and computational work, and we suggest other ion-neutral reactions with HCNH⁺ that have not been included in previous models of Titan’s ionosphere.     

Hydrogen Sulfide Induced Carbon Dioxide Activation by Metal‐Free Dual Catalysis

The role of metal free dual catalysis in the hydrogen sulfide (H₂S)‐induced activation of carbon dioxide (CO₂) and subsequent decomposition of resulting monothiolcarbonic acid in the gas phase has been explored. The results suggest that substituted amines and monocarboxylic type organic or inorganic acids via dual activation mechanisms promote both activation and decomposition reactions, implying that the judicious selection of a dual catalyst is crucial to the efficient C?S bond formation via CO₂ activation. Considering that our results also suggest a new mechanism for the formation of carbonyl sulfide from CO₂ and H₂S, these new insights may help in better understanding the coupling between the carbon and sulfur cycles in the atmospheres of Earth and Venus.     

Microchip capillary electrophoresis instrumentation for in situ analysis in the search for extraterrestrial life

The search for signs of life on extraterrestrial planetary bodies is among NASA's top priorities in Solar System exploration. The associated pursuit of organics and biomolecules as evidence of past or present life demands in situ investigations of planetary bodies for which sample return missions are neither practical nor affordable. These in situ studies require instrumentation capable of sensitive chemical analyses of complex mixtures including a broad range of organic molecules. Instrumentation must also be capable of autonomous operation aboard a robotically controlled vehicle that collects data and transmits it back to Earth. Microchip capillary electrophoresis (μCE) coupled to laser-induced fluorescence (LIF) detection provides this required sensitivity and targets a wide range of relevant organics while offering low mass, volume, and power requirements. Thus, this technology would be ideally suited for in situ studies of astrobiology targets, such as Mars, Europa, Enceladus, and Titan. In this review, we introduce the characteristics of these planetary bodies that make them compelling destinations for extraterrestrial astrobiological studies, and the principal groups of organics of interest associated with each. And although the technology we describe here was first developed specifically for proposed studies of Mars, by summarizing its evolution over the past decade, we demonstrate how μCE-LIF instrumentation has become an ideal candidate for missions of exploration to all of these nearby worlds in our Solar System.     

One Collision—Two Substituents: Gas-Phase Preparation of Xylenes under Single-Collision Conditions

The fundamental reaction pathways to the simplest dialkylsubstituted aromatics—xylenes (C₆H₄(CH₃)₂)—in high-temperature combustion flames and in low-temperature extraterrestrial environments are still unknown, but critical to understand the chemistry and molecular mass growth processes in these extreme environments. Exploiting crossed molecular beam experiments augmented by state-of-the-art electronic structure and statistical calculations, this study uncovers a previously elusive, facile gas-phase synthesis of xylenes through an isomer-selective reaction of 1-propynyl (methylethynyl, CH₃CC) with 2-methyl-1,3-butadiene (isoprene, C₅H₈). The reaction dynamics are driven by a barrierless addition of the radical to the diene moiety of 2-methyl-1,3-butadiene followed by extensive isomerization (hydrogen shifts, cyclization) prior to unimolecular decomposition accompanied by aromatization via atomic hydrogen loss. This overall exoergic reaction affords a preparation of xylenes not only in high-temperature environments such as in combustion flames and around circumstellar envelopes of carbon-rich Asymptotic Giant Branch (AGB) stars, but also in low-temperature cold molecular clouds (10 K) and in hydrocarbon-rich atmospheres of planets and their moons such as Triton and Titan. Our study established a hitherto unknown gas-phase route to xylenes and potentially more complex, disubstituted benzenes via a single collision event highlighting the significance of an alkyl-substituted ethynyl-mediated preparation of aromatic molecules in our Universe.     

Charge induced closing of Dionaea muscipula Ellis trap

In terms of bioelectrochemistry, Venus flytrap responses can be considered in three stages: stimulus perception, electrical signal transmission, and induction of mechanical and biochemical responses. When an insect touches the trigger hairs, these mechanosensors generate receptor potentials, which induce solitary waves activating the motor cells. We found that the electrical charge injected between a midrib and a lobe closes the Venus flytrap leaf by activating motor cells without mechanical stimulation of trigger hairs. The mean electrical charge required for the closure of the Venus flytrap leaf is 13.6 muC. To close the trap, electrical charge can be submitted as a single charge or applied cumulatively by small portions during a short period of time. Ion channel blocker such as Zn(2+) as well as an uncoupler CCCP, dramatically decreases the speed of the trap closing a few hours after treatment of the soil. This effect is reversible. After soil washing by distilled water, the closing time of Venus flytrap treated by CCCP or ZnCl(2) decreases back from 2-5 s to 0.3 s, but higher electrical charge is needed for trap closure. The mechanism behind closing the upper leaf of Venus flytrap is discussed.     

Structural investigation of Titan tholins by solution-state 1H, 13C, and 15N NMR: one-dimensional and decoupling experiments

Titan, the largest moon of Saturn, is enveloped in a reddish brown organic haze. Titan haze is presumed to be formed from methane and nitrogen (CH(4) and N(2)) in Titan's upper atmosphere through energetic photochemistry and particle bombardment. Though Titan haze has been directly investigated using methods including the Cassini mission, its formation mechanism and the contributing chemical structures and prebiotic potential are still not well developed. We report here the structural investigation of the (13)C and (15)N labeled, simulated Titan haze aerosol (tholin) by solution-state NMR. The one-dimensional (1)H, (13)C, and (15)N NMR spectra and decoupling experiments indicate that the tholin sample contains amine, nitrile, imine, and N-heteroaromatic compounds of tremendous import in understanding complex organic chemistry in anaerobic, extraterrestrial environments.     

Tailoring Polymers for Entry into the Atmospheres of Mars and Venus

Abstract

Exploring the other planets of our solar system with atmospheric probes and landers places new requirements on polymeric systems. Because of a preoccupation with weight, designers of capsule components are switching over to plastics with increasing frequency. Ablative heat shields, aeroshell structures, antennas, insulators, electronics packaging, parachutes, and many specialty items could be made from plastics which are tailored to the specific environmental needs. In spite of generally poor practices which limit the reproducibility of commercial products, much is being done to delineate the problems set forth by these environments. This paper outlines the specific environments expected for Mars and Venus capsules and discusses some of the efforts in process, or prospective, within or for the National Aeronautics and Space Administration (NASA), to provide the understanding necessary to tailor new composites for these specific environments. Although much of the work is oriented toward ablative heat shield development, the application is generally similar for all of the other capsule components. Based on this work, an idealized polymer would be a reproducible high-temperature plastic with low volatile content, low-temperature flexibility, and a low number of reactive sites after cure. Though we are some distance from this ideal, progress is being made toward this objective.     

Stabilities of some silicate minerals under approximate venusian surface conditions

Stability field diagrams have been constructed for forsterite, enstatite, wollastonite, and their precursors and reaction products under 90 atm CO₂ at 427°C, approximating the environment on Venus. The compounds were also studied experimentally under similar conditions. The results show that forsterite and enstatite are stable but that wollastonite is not. Periclase and magnesite undergo reaction, the former to magnesite and the latter to synthetic forsterite. Calcite is stable.     

A possible construction of a complex chemical reaction network

A procedure is suggested for the construction of chemical reaction networks. We define the kinetic communication as a transfer of atoms or atomic groups between two species and determine all the kinetic communications occurring in the possible mechanism of a complex chemical process. The set of kinetic communications is the basis of the communication matrices resulting in the complete network of the overall reaction.Limiting the consideration for certain types of kinetic communications we obtain the reaction subnetworks and selecting arbitrarily species among those participating in the possible mechanism we introduced the concept of the partial subnetworks which correspond to subsets of the complete network.By the simple analysis of the subnetworks it is easy to obtain the sequence network indicating the pathways via which the selected species are formed in the course of the overall process, by the transfer of chosen atoms or atomic groups.     

氧化反应对胜利褐煤水蒸气气化反应的促进作用Ⅰ:宏观反应特性研究

在φ80×3 000mm耐高温不锈钢管气流床反应器中,以150-180μm胜利褐煤为气化原料,考察了800和900℃时添加氧气前后褐煤转化率的变化,研究了氧化反应对水蒸气气化反应影响的宏观特征。结果表明,添加氧气后褐煤转化率明显大于O_2和H_2O气氛下褐煤转化率之和,即向水蒸气气氛添加氧气后褐煤转化率的增幅大于氧气氧化作用导致的褐煤转化率的增幅,随着H_2O含量增大以及温度的升高此现象愈加明显。该协同作用主要是氧化反应对水蒸气气化反应的促进作用造成的。利用φ40×200 mm石英圆筒流化床反应器进行了类似的实验,也发现了该协同作用。同时,借鉴收缩核模型并结合气流床气化实验条件推导了水蒸气气化宏观动力学方程,得到的速率方程(Z-(1-x))~(1/3)=(tβk_(H_2O)/Rρ_C)φ_(H_2O)=K_(H_2Oφ_(H_2O))与实验值吻合较好,添加氧气后水蒸气气化反应速率和水蒸气气化反应表观速率常数K_(H_2O)明显增大,这是氧气对水蒸气气化反应促进作用的动力学特征。     

The kinetics study of the S + S2 → S3 reaction by the chaperone mechanism

The recombination of S atoms has been found to be stepwise from the smallest unit, the elemental S atom, to the most abundant molecule S(8). The reaction between S + S(2) → S(3) has not been reported either experimentally or by theory, but may be a key intermediate step in the formation of sulfur aerosols in low-O(2) atmospheres. In this work, the kinetics of this reaction is reported with Ar gas used as the chaperone molecule in the production of S(3) via two complex intermediates: SAr + S(2) and S(2)Ar + S. Quasi-classical and classical trajectory methods are used. The rate constant of the S + S(2) + Ar → S(3) + Ar reaction is determined to be 2.66 × 10(-33) cm(6) mol(-1)?s(-1) at 298.15 K. The temperature dependence of the reaction is found to be 2.67 × 10(-33) exp[143.56(1∕T-1∕298.15)]. The second-order rate constant of S + S(2) → S(3) is 6.47 × 10(-14) cm(3)?molecule(-1)?s(-1) at 298.15 K and the Arrhenius-type rate constant is calculated to be 6.25 × 10(-14) exp[450.15(1∕T-1∕298.15)] cm(3)?molecule(-1)?s(-1). This work provides a rate coefficient for a key intermediate species in studies of sulfur formation in the modern Venus atmosphere and the primitive Earth atmosphere, for which assumed model rate coefficients have spanned nearly 4 orders of magnitude. Although a symmetry-induced mass-independent isotope effect is not expected for a chaperone mechanism, the present work is an important step toward evaluating whether mass-independence is expected for thiozone formation as is observed for ozone formation.