Carbon dioxide–water clusters in the atmosphere of Mars

This work assesses the potential of new water cluster-based ion beams for improving the capabilities of secondary ion mass spectrometry (SIMS) for in situ lipidomics. The effect of water clusters was compared to carbon dioxide clusters, along with the effect of using pure water clusters compared to mixed water and carbon dioxide clusters. A signal increase was found when using pure water clusters. However, when analyzing cells, a more substantial signal increase was found in positive ion mode when the water clusters also contained carbon dioxide, suggesting that additional reactions are in play. The effects of using a water primary ion beam on a more complex sample were investigated by analyzing brain tissue from an Alzheimer’s disease transgenic mouse model. The results indicate that the ToF-SIMS results are approaching those from MALDI as ToF-SIMS was able to image lyso-phosphocholine (LPC) lipids, a lipid class that for a long time has eluded detection during SIMS analyses. Gangliosides, sulfatides, and cholesterol were also imaged.Graphical abstract

Proton mobility and stability of water clusters containing alkali metal ions

Temperature dependent energies of formation for hydrogen-bonded water clusters using a modified mndo and a statistical mechanics approach

The stability of water clusters containing nitrogen oxide molecules is studied by the molecular dynamics method. The composition and size of thermodynamically stable heteroclusters are determined. The inclusion of two molecules of nitrogen oxide into aggregates containing seven or more water molecule increases the cluster stability. The correlation between the stability of heteroclusters and the ratio of self-diffusion coefficients of molecules of different kinds is observed. The real part of the cluster permittivity is maximal in the vicinity of the frequency of 200 cm–1. The inclusion of nitrogen oxide molecules into water clusters increases the characteristic frequency of dielectric relaxation. In general, heteroclusters are more stable with respect to perturbations caused by an external electric field than pure clusters with the same number of water molecules. The clusterization of water vapors accompanied by absorption of polar molecules of impurity favors a decrease in the greenhouse effect.

Water cluster formation and methane adsorption within a hydrophobic porous metal organic framework is studied by in situ vibrational spectroscopy, adsorption isotherms, and first-principle DFT calculations (using vdW-DF). Specifically, the formation and stability of H2O clusters in the hydrophobic cavities of a fluorinated metal-organic framework (FMOF-1) is examined. Although the isotherms of water show no measurable uptake (see Yang et al. J. Am. Chem. Soc. 2011 , 133 , 18094 ), the large dipole of the water internal modes makes it possible to detect low water concentrations using IR spectroscopy in pores in the vicinity of the surface of the solid framework. The results indicate that, even in the low pressure regime (100 mTorr to 3 Torr), water molecules preferentially occupy the large cavities, in which hydrogen bonding and wall hydrophobicity foster water cluster formation. We identify the formation of pentameric water clusters at pressures lower than 3 Torr and larger clusters beyond that pressure. The binding energy of the water species to the walls is negligible, as suggested by DFT computational findings and corroborated by IR absorption data. Consequently, intermolecular hydrogen bonding dominates, enhancing water cluster stability as the size of the cluster increases. The formation of water clusters with negligible perturbation from the host may allow a quantitative comparison with experimental environmental studies on larger clusters that are in low concentrations in the atmosphere. The stability of the water clusters was studied as a function of pressure reduction and in the presence of methane gas. Methane adsorption isotherms for activated FMOF-1 attained volumetric adsorption capacities ranging from 67 V(STP)/V at 288 K and 31 bar to 133 V(STP)/V at 173 K and 5 bar, with an isosteric heat of adsorption of ca. 14 kJ/mol in the high temperature range (288-318 K). Overall, the experimental and computational data suggest high preferential uptake for methane gas relative to water vapor within FMOF-1 pores with ease of desorption and high framework stability under operative temperature and moisture conditions.

1.1 Carbon dioxide 1.1.1 Significance Theoretical and experimental investigations of weakly bound molecular complexes are of fundamental importance for understanding of molecular interactions responsible for properties of condensed phases. The carbon dioxide clusters provide a simple model for such studies. Carbon dioxide has been a subject of many papers in recent years. Some deal with its role in the biosphere, mainly the greenhouse effect. The greenhouse effect is the rise in temperature that the Earth experiences because certain gases in the atmosphere (water vapor, carbon dioxide, nitrous oxide, and methane, for example) trap energy from the sun. Without these gases, heat would escape back into space and Earth’s average temperature would be lower. Other investigations deal with the significance of carbon dioxide for the nutrition for plants, the supercritical carbon dioxide as a green solvent for extraction and synthesis and the existance of carbon dioxide in the atmospheres of Mars and Venus. 1.1.2 Previous Investigations The carbon dioxide dimer was first detected in 1966 by Leckenby et al.[?]. The slippedparallel( C2h - geometry) structure of the carbon dioxide dimer was shown experimentally in references [?] - [?](high-resolution infrared) and [?](Raman studies) to be the stable one. That the structure of the dimer is slipped-parallel(C2h - geometry) was shown in [?] as a result of quantum-chemical calculations. The dimerisation equilibrium constant was evaluated using partition functions [?]. 1.1.3 Dimer formation A new method is developed to calculate the equilibrium constant of weak dimer complexes and the life time of the dimer in the gas phase. Actually it is not an easy task to define when approaching monomers form a dimer. In the new method the defined time correlation function from the molecular dynamics simulations shows a slow decay corresponding to real dimers and a fast decay corresponding to unstable collisions. The results obtained for the carbon dioxide dimerization are compared to results obtained by two other methods using partition function and second virial coefficient. A possible application is to predict the dimer carbon dioxide concentration in the atmospheres of Mars and Venus. 1.2 Rebinding dynamics of nitric oxide to the V68F Myoglobin mutant In connection with the work on rebinding molecular dynamics of nitric oxide to the V68F Myoglobin mutant I would like to emphasize that the study of reactive processes in chemically and biologically relevant systems is a topic of much current interest. For fast reactions (proton transfer, ligand rebinding) computer simulations are a useful means to investigate and understand the energetics and dynamics of chemical reactions. A new surface-crossing algorithm suitable for describing bond-breaking and bond-forming processes in molecular dynamics simulations is presented in [?]. The method is formulated for two intersecting potential energy manifolds which dissociate to different adiabatic states. During simulations, crossings are detected by monitoring an energy criterion. If fulfilled, the two manifolds are mixed over a finite number of time steps, after which the system is propagated on the second adiabat and the crossing is carried out with probability one.

Structure, stability, and nature of bonding between high energy water clusters confined inside cucurbituril: A computational study

Stability of water clusters: Implication for atmospheric hydrated clusters and aerosols

Water Clusters in Amorphous Pharmaceuticals

A nozzle molecular beam is operated so as to optimize the molecular clustering in the free jet expansion. Continuous beams of carbon dioxide and water are sampled with an ionization gauge detector. The increased beam intensity under some operating conditions can only be attributed to clustering. A high energy electron beam of 39.5 keV is used to obtain Debye-Scherrer diffraction patterns from carbon dioxide and water clusters. The largest size clusters produced are solid and have the structure of the bulk material which is simple cubic for CO2 and diamond cubic for H2O. The average diameters for CO2 and H2O are 52±5 and 54±5 Å, respectively, corresponding to 1600 and 2600 molecules per cluster. The CO2 data are in agreement with other beam results and, to the authors' knowledge, these are the first data published on the structure of water clusters formed from the vapor phase via homogeneous nucleation. Based on the diffraction data the structure of clusters down to average sizes in the range of 300–450 molecules per cluster can be treated as bulk phase.

The formation of the cyclic carbon trioxide isomer, CO3(X 1A1), in carbon-dioxide-rich extraterrestrial ices and in the atmospheres of Earth and Mars were investigated experimentally and theoretically. Carbon dioxide ices were deposited at 10 K onto a silver (111) single crystal and irradiated with 5 keV electrons. Upon completion of the electron bombardment, the samples were kept at 10 K and were then annealed to 293 K to release the reactants and newly formed molecules into the gas phase. The experiment was monitored via a Fourier transform infrared spectrometer in absorption-reflection-absorption (solid state) and through a quadruple mass spectrometer (gas phase) on-line and in situ. Our investigations indicate that the interaction of an electron with a carbon dioxide molecule is dictated by a carbon–oxygen bond cleavage to form electronically excited (1D) and/or ground state (3P) oxygen atoms plus a carbon monoxide molecule. About 2% of the oxygen atoms react with carbon dioxide molecules to form the C2v symmetric, cyclic CO3 structure via addition to the carbon–oxygen double bond of the carbon dioxide species; neither the Cs nor the D3h symmetric isomers of carbon trioxide were detected. Since the addition of O(1D) involves a barrier of a 4–8 kJ mol−1 and the reaction of O(3P) with carbon dioxide to form the carbon trioxide molecule via triplet-singlet intersystem crossing is endoergic by 2 kJ mol−1, the oxygen reactant(s) must have excess kinetic energy (suprathermal oxygen atoms which are not in thermal equilibrium with the surrounding 10 K matrix). A second reaction pathway of the oxygen atoms involves the formation of ozone via molecular oxygen. After the irradiation, the carbon dioxide matrix still stores ground state oxygen atoms; these species diffuse even at 10 K and form additional ozone molecules. Summarized, our investigations show that the cyclic carbon trioxide isomer, CO3(X 1A1), can be formed in low temperature carbon dioxide matrix via addition of suprathermal oxygen atoms to carbon dioxide. In the solid state, CO3(X 1A1) is being stabilized by phonon interactions. In the gas phase, however, the initially formed C2v structure is rovibrationally excited and can ring-open to the D3h isomer which in turn rearranges back to the C2v structure and then loses an oxygen atom to ‘recycle’ carbon dioxide. This process might be of fundamental importance to account for an 18O enrichment in carbon dioxide in the atmospheres of Earth and Mars.

Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases. By further calculations of the nucleation rate and the growth rate of water cluster, it is found that the decrease of average size results from a high nucleation rate and a low size growth rate in the downstream of gas flow far away from conical nozzle throat. Formation of pure gaseous water cluster in the supersonic gas flow from a conical nozzle was investigated by simulation. The simulation results show that average size of water cluster indicates a different size evolution along the gas flow, i.e., the average cluster size firstly increases to a maximum size and then decreases slowly, rather than keeps increasing like other gases.

TDLAS a laser diode sensor for the in situ monitoring of H 2O, CO 2 and their isotopes in the Martian atmosphere

Carbon dioxide gas is recognized among principal absorbers of radiation in the Earth's atmosphere. Moreover, carbon dioxide molecules are ubiquitous in the Universe. Being a dominant gas phase constituent in the atmospheres of Mars and Venus, carbon dioxide is responsible for a variety of physico-chemical processes in atmospheres of these terrestrial group planets. Weak intermolecular interaction among carbon dioxide molecules results in formation of van der Waals complexes or dimers. Estimates show that (CO 2 ) 2 dimers are the most abundant constituent in the surface layers of Venusian atmosphere after CO 2 itself. Although carbon dioxide in the gas phase is not appreciably abundant in the interstellar media, recent spectroscopic observations provide strong indications of widespread CO 2 -ices and CO 2 -rich ice mantles in molecular clouds. All these justify carrying out extensive experimental and theoretical studies of the carbon dioxide molecules in pairwise and higher order interactions. Crucial role in these investigations belongs to laboratory spectroscopic studies which imply a variety of methods, tools and external parameters. Present paper aims at reviewing infrared and Raman spectroscopy of CO 2 dimers formed in adiabatically cooled flows, in a pressurized static gas sample, and while trapped in low-temperature matrices.

The electronic effects that govern the cohesion of water clusters are complex, demanding the inclusion of N-body, Coulomb, exchange and correlation effects. Here we present a much needed quantitative study of the effect of correlation (and hence dispersion) energy on the stabilization of water clusters. For this purpose we used a topological energy partitioning method called Interacting Quantum Atoms (IQA) to partition water clusters into topological atoms, based on a MP2/6-31G(d,p) wave function, and modified versions of GAUSSIAN09 and the Quantum Chemical Topology (QCT) program MORFI. Most of the cohesion in the water clusters provided by electron correlation comes from intramolecular energy stabilization. Hydrogen bond-related interactions tend to largely cancel each other. Electron correlation energies are transferable in almost all instances within 1 kcal mol-1 . This observed transferability is very important to the further development of the QCT force field FFLUX, especially to the future modelling of liquid water.