Composition and Structure of the Martian Atmosphere: Preliminary Results from Viking 1

Bimolecular reactions of CH2CN2+ with Ar, N2 and CO: reactivity and dynamics

The reactivity, energetics and dynamics of bimolecular reactions between CH₂CN²⁺ and three neutral species (Ar, N₂ and CO) have been studied using a position sensitive coincidence methodology at centre-of-mass collision energies of 4.3-5.0 eV. This is the first study of bimolecular reactions involving CH₂CN²⁺, a species relevant to the ionospheres of planets and satellites, including Titan. All of the collision systems investigated display two collision-induced dissociation (CID) channels, resulting in the formation of C⁺ + CH₂N⁺ and H⁺ + HC₂N⁺. Evidence for channels involving further dissociation of the CID product HC₂N⁺, forming H + CCN⁺, were detected in the N₂ and CO systems. Proton-transfer from the dication to the neutral species occurs in all three of the systems via a direct mechanism. Additionally, there are product channels resulting from single electron transfer following collisions of CH₂CN²⁺ with both N₂ and CO, but interestingly no electron transfer following collisions with Ar. Electronic structure calculations of the lowest energy electronic states of CH₂CN²⁺ reveal six local geometric minima: both doublet and quartet spin states for cyclic, linear (CH₂CN), and linear isocyanide (CH₂NC) molecular geometries. The lowest energy electronic state was determined to be the doublet state of the cyclic dication. The ready generation of C⁺ ions by collision-induced dissociation suggests that the cyclic or linear isocyanide dication geometries are present in the [CH₂CN]²⁺ beam.

Bimolecular reactions of S2+ with Ar, H2 and N2: reactivity and dynamics

The reactivity, energetics and dynamics of bimolecular reactions between S²⁺ and three neutral species (Ar, H₂ and N₂) have been studied using a position-sensitive coincidence methodology at centre-of-mass collision energies below 6 eV. This is the first study of bimolecular reactions involving S²⁺, a species detected in planetary ionospheres, the interstellar medium, and in anthropogenic manufacturing processes. The reactant dication beam employed consists predominantly of S²⁺ in the ground ³P state, but some excited states are also present. Most of the observed reactions involve the ground state of S²⁺, but the dissociative electron transfer reactions appear to exclusively involve excited states of this atomic dication. We observe exclusively single electron-transfer between S²⁺ and Ar, a process which exhibits strong forward scatting typical of the Landau-Zener style dynamics observed for other dicationic electron transfer reactions. Following collisions between S²⁺ + H₂, non-dissociative and dissociative single electron-transfer reactions were detected. The dynamics here show evidence for the formation of a long-lived collision complex, [SH₂]²⁺, in the dissociative single electron-transfer channel. The formation of SH⁺ was not observed. In contrast, the collisions of S²⁺ + N₂ result in the formation of SN⁺ + N⁺ in addition to the products of single electron-transfer reactions.

FIELDABLE MASS SPECTROMETRY FOR FORENSIC SCIENCE, HOMELAND SECURITY, AND DEFENSE APPLICATIONS

Mass spectrometry is commonly used in forensic chemistry laboratories for sensitive, definitive analysis. There have been significant efforts to bring mass spectrometry analysis on-site through the development of ruggedized, fieldable instruments. Testing samples in the field is of particular interest in forensic science, homeland security, and defense applications. In forensic chemistry, testing seized drugs in the field can significantly improve efficiencies in processing of related criminal cases. The screening of passengers and luggage at transportation hubs is a critical need for homeland security for which mass spectrometry is well suited to provide definitive answers with low false positive rates. Mass spectrometry can yield reliable data for military personnel testing sites for potential chemical weapons release. To meet the needs of the forensic and security communities fieldable mass spectrometers based on membrane inlet systems and hybrid gas chromatography systems have been developed and commercialized. More recently developed ambient ionization mass spectrometry methods can eliminate the time, equipment, and expertise associated with sample preparation, and so are especially appealing for on-site analysis. We describe the development of fieldable mass spectrometry systems, with emphasis on commercially available systems that have been deployed for on-site analysis of seized drugs, chemical warfare agents, explosives, and other analytes of interest to the forensic and security communities. © 2020 John Wiley & Sons Ltd. Mass Spec Rev.

Bond-forming and electron-transfer reactivity between Ar2+ and N2

Collisions between Ar2+ and N2 have been studied using a coincidence technique at a centre-of-mass (CM) collision energy of 5.1 eV. Four reaction channels generating pairs of monocations are observed: Ar+ + N2+, Ar+ + N+, ArN+ + N+ and N+ + N+. The formation of Ar+ + N2+ is the most intense channel, displaying forward scattering but with a marked tail to higher scattering angles. This scattering, and other dynamics data, is indicative of direct electron transfer competing with a 'sticky' collision between the Ar2+ and N2 reactants. Here Ar+ is generated in its ground (2P) state and N2+ is primarily in the low vibrational levels of the C2Σu+ state. A minor channel involving the initial population of higher energy N2+ states, lying above the dissociation asymptote to N+ + N, which fluoresce to stable states of N2+ is also identified. The formation of Ar+ + N+ by dissociative single electron transfer again reveals the involvement of two different pathways for the initial electron transfer (direct or complexation). This reaction pathway predominantly involves excited states of Ar2+ (1D and 1S) populating N2+* in its dissociative C2Σu+, 22Πg and D2Πg states. Formation of ArN+ + N+ proceeds via a direct mechanism. The ArN+ is formed, with significant vibrational excitation, in its ground (X3Σ-) state. Formation of N+ + N+ is also observed as a consequence of double electron transfer forming N22+. The exoergicity of the subsequent N22+ dissociation reveals the population of the A1Πu and D3Πg dication states.

MINIATURIZATION IN MASS SPECTROMETRY

Expectations for continuous miniaturization in mass spectrometry are not declining for years. Portable instruments are highly welcome by the industry, science, space agencies, forensic laboratories, and many other units. All are striving for the small, cheap, and as good as possible instruments. This review describes the recent developments of miniature mass spectrometers and also provides selected applications where these devices are used. Upcoming perspectives of further development are also discussed. @ 2019 John Wiley & Sons Ltd. Mass Spec Rev.

Bond-forming and electron-transfer reactivity between Ar2+ and O2

The reactivity, energetics and dynamics of the bimolecular reactions between Ar²⁺ and O₂ have been studied using a position sensitive coincidence methodology at a collision energy of 4.4 eV.

Structure and composition of the neutral upper atmosphere of Mars from the MAVEN NGIMS investigation

The Mars Atmosphere and Volatile EvolutioN (MAVEN) Neutral Gas and Ion Mass Spectrometer (NGIMS) provides sensitive detections of neutral gas and ambient ion composition. NGIMS measurements of nine atomic and molecular neutral species, and their variation with altitude, latitude, and solar zenith angle are reported over several months of operation of the MAVEN mission. Sampling NGIMS signals from multiple neutral species every several seconds reveals persistent and unexpectedly large amplitude density structures. The scale height temperatures are mapped over the course of the first few months of the mission from high down to midlatitudes. NGIMS measurements near the homopause of ⁴⁰Ar/N₂ ratios agree with those reported by the Sample Analysis at Mars investigation and allow the altitude of the homopause for the most abundant gases to be established.

Resistance of the Lichen Buellia frigida to Simulated Space Conditions during the Preflight Tests for BIOMEX--Viability Assay and Morphological Stability

Samples of the extremotolerant Antarctic endemite lichen Buellia frigida are currently exposed to low-Earth orbit-space and simulated Mars conditions at the Biology and Mars Experiment (BIOMEX), which is part of the ESA mission EXPOSE-R2 on the International Space Station and was launched on 23 July 2014. In preparation for the mission, several preflight tests (Experimental and Scientific Verification Tests, EVT and SVT) assessed the sample preparation and hardware integration procedures as well as the resistance of the candidate organism toward the abiotic stressors experienced under space and Mars conditions. Therefore, we quantified the post-exposure viability with a live/dead staining technique utilizing FUN-1 and confocal laser scanning microscopy (CLSM). In addition, we used scanning electron microscopy (SEM) to investigate putative patterns of morphological-anatomical damage that lichens may suffer under the extreme exposure conditions. The present results demonstrate that Buellia frigida is capable of surviving the conditions tested in EVT and SVT. The mycobiont showed lower average impairment of its viability than the photobiont (viability rates of >83% and >69%, respectively), and the lichen thallus suffered no significant damage in terms of thalline integrity and symbiotic contact. These results will become essential to substantiate and validate the results prospectively obtained from the returning space mission. Moreover, they will help assess the limits and limitations of terrestrial organisms under space and Mars conditions as well as characterize the adaptive traits that confer lichen extremotolerance.

The gated electrostatic mass spectrometer (GEMS): definition and preliminary results

GEMS is a new type of time-of-flight mass spectrometer based on an electrostatic energy analyzer. Mass resolution equals the energy analyzer kinetic energy resolution, which is set by its slit size. In GEMS, monochromatic ions enter the entrance slit at random times, and the gated ion deflection produced by the electrostatic field in the analyzer rejects ions that are inside the analyzer at gate onset, detecting those entering the analyzer after gate onset. This provides mass separation while overcoming the temporal and spatial spread problems typical of TOF applications. Paradoxically, GEMS works because all ion masses follow identical trajectories. GEMS is easily multiplied into two-dimensional arrays to increase sensitivity in space applications, requires relatively low voltages, and uses only a few electrical connections. Thus, it is easy to package GEMS as a small, low-power instrument for applications in harsh environments. A disadvantage of GEMS is that its output is the integral of the TOF spectrum and the derivative of the raw data must be taken, a procedure that is likely to add noise. A version of GEMS detecting un-deflected ions (u-GEMS) has been tested to demonstrate the time-integrated feature of the raw data but without the benefit of energy analysis. This paper describes GEMS implemented with the small deflection energy analyzer (SDEA), a compact version of the parallel plate energy analyzer. SDEA is described both analytically and with ion trajectory simulations using the ion trajectory simulation software SIMION; the results are then used to describe GEMS and compute its performance.

Laser mass spectrometric detection of extraterrestrial aromatic molecules: mini-review and examination of pulsed heating effects

Laser mass spectrometry is a powerful tool for the sensitive, selective, and spatially resolved analysis of organic compounds in extraterrestrial materials. Using microprobe two-step laser mass spectrometry (muL(2)MS), we have explored the organic composition of many different exogenous materials, including meteorites, interplanetary dust particles, and interstellar ice analogs, gaining significant insight into the nature of extraterrestrial materials. Recently, we applied muL(2)MS to analyze the effect of heating caused by hypervelocity particle capture in aerogel, which was used on the NASA Stardust Mission to capture comet particles. We show that this material exhibits complex organic molecules upon sudden heating. Similar pulsed heating of carbonaceous materials is shown to produce an artifactual fullerene signal. We review the use of muL(2)MS to investigate extraterrestrial materials, and we discuss its recent application to characterize the effect of pulsed heating on samples of interest.

Ion optical evaluation of a miniature double-focusing mass spectrograph

A new miniature double-focusing mass spectrograph has been designed and constructed. The ion optical system was designed based on Mattauch-Herzog geometry. The mass spectrograph employs a focal plane detector consisting of a microchannel plate, a phosphor layer, a fiber-optic plate and a charge-coupled device. For the evaluation of the ion optics of the instrument, the energy and angular focal planes were investigated both experimentally and by simulation. Double focusing was satisfactorily achieved along a straight line over a wide mass range, and the experimental and simulated results were mutually consistent. A second-order element of the transfer matrix was also measured experimentally and proved to be in good agreement with the simulated result.

Small mass spectrometer with extended measurement capabilities at high pressures

For the in situ investigation of planetary atmospheres a small Mattauch-Herzog mass spectrometer has been developed. Its high-pressure performance has been improved by incorporating differential pumping between the ion source and the analyzing fields, shortening the path-length as well as increasing the extraction field in the ion source. In addition doubly ionized and dissociated ions are used for mass analysis. These measures make possible operation up to 10(-2) millibars. Results of laboratory tests related to linearity, dynamic range, and mass resolution are presented, in particular for CO(2).

Atomic Hydrogen on Mars: Measurements at Solar Minimum

The Copernicus Orbiting Astronomical Observatory was used to obtain measurements of Mars Lyman-alpha (1215.671-angstrom) emission at the solar minimum, which has resulted in the first information on atomic hydrogen concentrations in the upper atmosphere of Mars at the solar minimum. The Copernicus measurements, coupled with the Viking in situ measurements of the temperature (170 degrees +/- 30 degrees K) of the upper atmosphere of Mars, indicate that the atomic hydrogen number density at the exobase of Mars (250 kilometers) is about 60 times greater than that deduced from Mariner 6 and 7 Lyman-alpha measurements obtained during a period of high solar activity. The Copernicus results are consistent with Hunten's hypothesis of the diffusion-limited escape of atomic hydrogen from Mars.

Viking gas chromatograph-mass spectrometer

The Mars viking gas chromatograph-mass spectrometer is described. The system is designed to determine the composition of the Martian atmosphere and detect and identify chemical compounds vaporized or pyrolyzed from the Martian soil. Construction details, performance data, data processing methods, and references to manufacturing and test procedures are also provided.

Occultation of ε Geminorum by Mars: Evidence for Atmospheric Tides?

Temperature profiles of the martian atmosphere have been derived from airborne observations of the 8 April 1976 occultation of epsilon Geminorum. Within the altitude range from 50 to 90 kilometers, these profiles show peak-to-peak variations of 35 degrees K with a vertical scale of 20 kilometers and represent evidence for strong tides in the martian atmosphere. However, more information is necessary to conclusively rule out a radiative explanation for the temperature variations.

Structure of Mars' Atmosphere up to 100 Kilometers from the Entry Measurements of Viking 2

The Viking 2 entry science data on the structure of Mars' atmosphere up to 100 kilometers define a morning atmosphere with an isothermal region near the surface; a surface pressure 10 percent greater than that recorded simultaneously at the Viking 1 site, which implies a landing site elevation lower by 2.7 kilometers than the reference ellipsoid; and a thermal structure to 100 kilometers at least qualitatively consistent with pre-Viking modeling of thermal tides. The temperature profile exhibits waves whose amplitude grows with altitude, to approximately 25 degrees K at 90 kilometers. These waves are believed to be a consequence of layered vertical oscillations and associated heating and cooling by compression and expansion, excited by the daily thermal cycling of the planet surface. As is necessary for gravity wave propagation, the atmosphere is stable against convection, except possibly in some very local regions. Temperature is everywhere appreciably above the carbon dioxide condensation boundary at both landing sites, precluding the occurrence of carbon dioxide hazes in northern summer at latitudes to at least 50 degrees N. Thus, ground level mists seen in these latitudes would appear to be condensed water vapor.

Scientific Results of the Viking Missions

The two Viking missions to Mars have been extraordinarily successful. Thirteen scientific investigations yielded information about the atmosphere and surface. Two orbiters and landers operating for several months photographed the surface extensively from 1500 kilometers and directly on the surface. Measurements were made of the atmospheric composition, the surface elemental abundance, the atmospheric water vapor, temperature of the surface, and meteorological conditions; direct tests were made for organic material and living organisms. The question of life on Mars remains unanswered. The Viking spacecraft are designed to continue the investigations for at least one Mars year.

Composition and Structure of the Martian Upper Atmosphere: Analysis of Results from Viking

Densities for carbon dioxide measured by the upper atmospheric mass spectrometers on Viking 1 and Viking 2 are analyzed to yield height profiles for the temperature of the martian atmosphere between 120 and 200 kilometers. Densities for nitrogen and argon are used to derive vertical profiles for the eddy diffusion coefficient over the same height range. The upper atmosphere of Mars is surprisingly cold with average temperatures for both Viking 1 and Viking 2 of less than 200 degrees K, and there is significant vertical structure. Model calculations are presented and shown to be in good agreement with measured concentrations of carbon monoxide, oxygen, and nitric oxide.

The Environs of Viking 2 Lander

Forty-six days after Viking 1 landed, Viking 2 landed in Utopia Planitia, about 6500 kilometers away from the landing site of Viking 1. Images show that in the immediate vicinity of the Viking 2 landing site the surface is covered with rocks, some of which are partially buried, and fine-grained materials. The surface sampler, the lander cameras, engineering sensors, and some data from the other lander experiments were used to investigate the properties of the surface. Lander 2 has a more homogeneous surface, more coarse-grained material, an extensive crust, small rocks or clods which seem to be difficult to collect, and more extensive erosion by the retro-engine exhaust gases than lander 1. A report on the physical properties of the martian surface based on data obtained through sol 58 on Viking 2 and a brief description of activities on Viking 1 after sol 36 are given.

Structure of the Neutral Upper Atmosphere of Mars: Results from Viking 1 and Viking 2

Neutral mass spectrometers carried on the aeroshells of Viking 1 and Viking 2 indicate that carbon dioxide is the major constituent of the martian atmosphere over the height range 120 to 200 kilometers. The atmosphere contains detectable concentrations of nitrogen, argon, carbon monoxide, molecular oxygen, atomic oxygen, and nitric oxide. The upper atmosphere exhibits a complex and variable thermal structure and is well mixed to heights in excess of 120 kilometers.

Temperatures of the Martian Surface and Atmosphere: Viking Observation of Diurnal and Geometric Variations

Selected observations made with the Viking infrared thermal mapper after the first landing are reported. Atmospheric temperatures measured at the latitude of the Viking 2 landing site (48 degrees N) over most of a martian day reveal a diurnal variation of at least 15 K, with peak temperatures occurring near 2.2 hours after noon, implying significant absorption of sunlight in the lower 30 km of the atmosphere by entrained dust. The summit temperature of Arsia Mons varies by a factor of nearly two each day; large diurnal temperature variation is characteristic of the south Tharsis upland and implies the presence of low thermal inertia material. The thermal inertia of material on the floors of several typical large craters is found to be higher than for the surrounding terrain; this suggests that craters are somehow effective in sorting aeolian material. Brightness temperatures of the Viking 1 landing area decrease at large emission angles; the intensity of reflected sunlight shows a more complex dependence on geometry than expected, implying atmospheric as well as surface scattering.

Isotopic Composition of the Martian Atmosphere

Results from the neutral mass spectrometer carried on the aeroshell of Viking 1 show evidence for NO in the upper atmosphere of Mars and indicate that the isotopic composition of carbon and oxygen is similar to that of Earth. Mars is enriched in (15)N relative to Earth by about 75 percent, a consequence of escape that implies an initial abundance of nitrogen equivalent to a partial pressure of at least 2 millibars. The initial abundance of oxygen present either as CO(2) or H(2)O must be equivalent to an exchangeable atmospheric pressure of at least 2 bars in order to inhibit escape-related enrichment of (18)O.

Isotopic Composition of Nitrogen: Implications for the Past History of Mars' Atmosphere

Models are presented for the past history of nitrogen on Mars based on Viking measurements showing that the atmosphere is enriched in (15)N. The enrichment is attributed to selective escape, with fast atoms formed in the exosphere by electron impact dissociation of N(2) and by dissociative recombination of N(2)(+). The initial partial pressure of N(2) should have been at least as large as several millibars and could have been as large as 30 millibars if surface processes were to represent an important sink for atmospheric HNO(2) and HNO(3).