Water Ice Matrix Research Articles

Upper limits on the water vapour content of the β Pictoris debris disk

Context. The debris disk surrounding β Pictoris has been observed with ALMA to contain a belt of CO gas with a distinct peak at ~85 au. This CO clump is thought to be the result of a region of enhanced density of solids that collide and release CO through vaporisation. The parent bodies are thought to be comparable to solar system comets, in which CO is trapped inside a water ice matrix. Aims. Since H2O should be released along with CO, we aim to put an upper limit on the H2O gas mass in the disk of β Pictoris. Methods. We used archival data from the Heterodyne Instrument for the Far-Infrared (HIFI) aboard the Herschel Space Observatory to study the ortho-H2O 110–101 emission line. The line is undetected. Using a python implementation of the radiative transfer code RADEX, we converted upper limits on the line flux to H2O gas masses. The resulting lower limits on the CO/H2O mass ratio are compared to the composition of solar system comets. Results. Depending on the assumed gas spatial distribution, we find a 95% upper limit on the ortho-H2O line flux of 7.5 × 10−20 W m−2 or 1.2 × 10−19 W m−2. These translate into an upper limit on the H2O mass of 7.4 × 1016–1.1 × 1018 kg depending on both the electron density and gas kinetic temperature. The range of derived gas-phase CO/H2O ratios is marginally consistent with low-ratio solar system comets.

WATSON: In Situ Organic Detection in Subsurface Ice Using Deep-UV Fluorescence Spectroscopy.

Terrestrial icy environments have been found to preserve organic material and contain habitable niches for microbial life. The cryosphere of other planetary bodies may therefore also serve as an accessible location to search for signs of life. The Wireline Analysis Tool for the Subsurface Observation of Northern ice sheets (WATSON) is a compact deep-UV fluorescence spectrometer for nondestructive ice borehole analysis and spatial mapping of organics and microbes, intended to address the heterogeneity and low bulk densities of organics and microbial cells in ice. WATSON can be either operated standalone or integrated into a wireline drilling system. We present an overview of the WATSON instrument and results from laboratory experiments intended to determine (i) the sensitivity of WATSON to organic material in a water ice matrix and (ii) the ability to detect organic material under various thicknesses of ice. The results of these experiments show that in bubbled ice the instrument has a depth of penetration of 10 mm and a detection limit of fewer than 300 cells. WATSON incorporates a scanning system that can map the distribution of organics and microbes over a 75 by 25 mm area. WATSON demonstrates a sensitive fluorescence mapping technique for organic and microbial detection in icy environments including terrestrial glaciers and ice sheets, and planetary surfaces including Europa, Enceladus, or the martian polar caps.

Solid State Photochemistry of Hydroxylated Naphthalenes on Minerals: Probing Polycyclic Aromatic Hydrocarbon Transformation Pathways under Astrochemically-Relevant Conditions

Oxygenated derivatives of polycyclic aromatic hydrocarbons (PAHs), or oxyPAHs, recently captured the interest of the scientific community for their photochemical reactivity in a water–ice matrix mi...

Interaction of Acetonitrile with Water-Ice: An Infrared Spectroscopic Study

Interaction of water-ice and acetonitrile has been studied at low temperatures in their codeposited mixtures, in ultrahigh vacuum conditions. They interact strongly at low temperatures (in the temperature range of 40–110 K), which was confirmed from the new features manifested in the reflection absorption infrared spectra of the mixtures. This interaction was attributed to strong hydrogen bonding which weakens upon warming as the acetonitrile molecules phase segregate from water-ice. Complete phase separation was observed at 130 K prior to desorption of acetonitrile from the water-ice matrix. Such a hydrogen-bonded structure is not observed when both the molecular solids are deposited as water on acetonitrile or acetonitrile on water overlayers. A quantitative analysis shows that in a 1:1 codeposited mixture, more than 50% acetonitrile molecules are hydrogen bonded with water-ice at low temperatures (40–110 K).

Ab initio simulation of pyrene spectra in water matrices

The absorption and emission spectra of free pyrene and pyrene in a water ice matrix were simulated ab initio with their vibronic profiles. Water ice was mimicked by a large cluster of explicit water molecules.

The formation of carbamate ions in interstellar ice analogues

Carbon dioxide and ammonia are two of the most abundant species in astrophysical media, where they can react in the solid phase under certain conditions. This contribution presents a study of this reaction both in the presence of water and for anhydrous samples. It is shown that after deposition at 15 K, the reaction can start by warming the deposit, and the process continues on up to a temperature of 220 K. Reaction products are studied using infrared spectroscopy and mass spectrometry. For anhydrous samples, a 2 : 1 stoichiometry mixture of NH3 : CO2 gives the highest yield of products. The reaction is favored when a small amount of water is present, which enables ammonia and carbon dioxide molecules to collide within the pores and channels of the amorphous water solid. Large concentration of water, on the other hand, hampers such collisions. The main reaction product is found to be ammonium carbamate, but also carbamic acid is formed, and, in the presence of water, ammonium bicarbonate is produced as well. Theoretical calculations are carried out to provide the basis for the assignment of the spectra. Some of the experiments presented in this contribution consist of the generation of a compact water ice matrix where the carbamate and ammonium ions are embedded. If such a system was found in astrophysical media, it is shown that the ammonium ion could not be detected, whereas two infrared features of the carbamate ion in the 1040 to 1115 cm(-1) (9 to 9.6 μm) region could enable the observation of this species.

ChemInform Abstract: Prebiotic Chemistry in Eutectic Solutions at the Water—Ice Matrix

AbstractReview: 123 refs.

Infrared Matrix-Assisted Laser Desorption/Ionization Orthogonal-Time-of-Flight Mass Spectrometry Employing a Cooling Stage and Water Ice As a Matrix

Although water ice has been utilized in the past as a matrix for infrared matrix-assisted laser desorption/ionization mass spectrometry (IR-MALDI-MS), it has not found a wider use due to limitations in the analytical performance and technical demands on the employment of the necessary cooling stage. Here, we developed a temperature-controlled sample stage for use with an orthogonal time-of-flight mass spectrometer (MALDI-o-TOF-MS). The stage utilizes a combination of liquid nitrogen cooling and counterheating with a Peltier element. It allows adjustment of the sample temperature between ~-120 °C and room temperature. To identify optimal irradiation conditions for IR-MALDI with the water ice matrix, we first investigated the influence of excitation wavelength, varied between 2.7 and 3.1 μm, and laser fluence on the signal intensities of molecular substance P ions. These data suggest the involvement of transient melting of the ice during the laser pulse and primary energy deposition into liquid water. As a consequence, the best analytical performance is obtained at a wavelength corresponding to the absorption maximum of liquid water of about 2.94 μm. The current data significantly surpass the previously reported analytical features. The particular softness of the method is, for example, exemplified by the analysis of noncovalently bound holo-myoglobin and of ribonuclease B. This is also the first report demonstrating the analysis of an IgG monoclonal antibody (MW ~ 150 kDa) from a water ice matrix. Untypical for MALDI-MS, high charge states of multiply protonated species were moreover observed for some of the investigated peptides and even for lacto-N-fucopentaose II oligosaccharides. Using water ice as matrix is of particular interest for MALDI MS profiling and imaging applications since matrix-free spectra are produced. The MS and tandem MS analysis of metabolites directly from frozen food samples is demonstrated with the example of a strawberry fruit.

Prebiotic chemistry in eutectic solutions at the water–ice matrix

A crystalline ice matrix at subzero temperatures can maintain a liquid phase where organic solutes and salts concentrate to form eutectic solutions. This concentration effect converts the confined reactant solutions in the ice matrix, sometimes making condensation and polymerisation reactions occur more favourably. These reactions occur at significantly high rates from a prebiotic chemistry standpoint, and the labile products can be protected from degradation. The experimental study of the synthesis of nitrogen heterocycles at the ice-water system showed the efficiency of this scenario and could explain the origin of nucleobases in the inner Solar System bodies, including meteorites and extra-terrestrial ices, and on the early Earth. The same conditions can also favour the condensation of monomers to form ribonucleic acid and peptides. Together with the synthesis of these monomers, the ice world (i.e., the chemical evolution in the range between the freezing point of water and the limit of stability of liquid brines, 273 to 210 K) is an under-explored experimental model in prebiotic chemistry.

Growth of thin films of low molecular weight proteins by matrix assisted pulsed laser evaporation (MAPLE)

Thin films of lysozyme and myoglobin grown by matrix assisted pulsed laser evaporation (MAPLE) from a water ice matrix have been investigated. The deposition rate of these two low molecular weight proteins (lysozyme: 14307 amu and myoglobin: 17083 amu) exhibits a maximum of about 1–2 ng/cm2 per pulse at a fluence of 1–2 J/cm2 and decreases slowly with increasing fluence. This rate is presumably determined by the matrix rather by the proteins. A significant fraction of the proteins are intact in the film as determined by MALDI (Matrix assisted laser desorption ionization) spectrometry. The results for lysozyme demonstrate that the fragmentation rate of the proteins during the MAPLE process is not influenced by the pH of the water solution prior to freezing.

Kinetics and mechanism of para-chlorophenol photoconversion with the presence of nitrite in ice

The photochemistry of para-chlorophenol (4-CP) under UV irradiation by using a 125-W high-pressure mercury lamp as light source with the presence of nitrite in a solid water ice matrix had been studied. The experiments were carried out in a photochemical cold chamber reactor at −14 to −12 °C. Each influence factor of the 4-CP photoconversion kinetics in the water ice was inspected. The results show that the 4-CP photoconversion obeys the first-order kinetics model and the initial concentration of 4-CP, the initial concentration of nitrite, pH value, light intensity, inorganic ions and the water quality all have significant influence on the photoconversion rate. In addition, nine intermediate products were characterized by GC–MS, HPLC–ESI-MS and HPLC techniques and the possible photoconversion mechanism was proposed accordingly. It is concluded that the mechanism and photoproducts of 4-CP photolysis in ice are changed due to the presence of NO 2 −.

Release of N2, CH4, CO2, and H2O from surface ices on Enceladus

Abstract We vapor deposit at 20 K a mixture of gases with the specific Enceladus plume composition measured in situ by the Cassini INMS [Waite, J.H., Combi, M.R., Ip, W.H., Cravens, T.E., McNutt, R.L., Kasprzak, W., Yelle, R., Luhmann, J., Niemann, H., Gell, D., Magee, B., Fletcher, G., Lunine, J., Tseng, W.L., 2006. Science 311, 1419–1422] to form a mixed molecular ice. As the sample is slowly warmed, we monitor the escaping gas quantity and composition with a mass spectrometer. Pioneering studies [Schmitt, B., Klinger, J., 1987. Different trapping mechanisms of gases by water ice and their relevance for comet nuclei. In: Rolfe, E.J., Battrick, B. (Eds.), Diversity and Similarity of Comets. SP-278. ESA, Noordwijk, The Netherlands, pp. 613–619; Bar-Nun, A., Kleinfeld, I., Kochavi, E., 1988. Phys. Rev. B 38, 7749–7754; Bar-Nun, A., Kleinfeld, I., 1989. Icarus 80, 243–253] have shown that significant quantities of volatile gases can be trapped in a water ice matrix well above the temperature at which the pure volatile ice would sublime. For our Enceladus ice mixture, a composition of escaping gases similar to that detected by Cassini in the Enceladus plume can be generated by the sublimation of the H 2 O:CO 2 :CH 4 :N 2 mixture at temperatures between 135 and 155 K, comparable to the high temperatures inferred from the CIRS measurements [Spencer, J.R., Pearl, J.C., Segura, M., Flasar, F.M., Mamoutkine, A., Romani, P., Buratti, B.J., Hendrix, A.R., Spilker, L.J., Lopes, R.M.C., 2006. Science 311, 1401–1405] of the Enceladus “tiger stripes.” This suggests that the gas escape phenomena that we measure in our experiments are an important process contributing to the gases emitted from Enceladus. A similar experiment for ice deposited at 70 K shows that both the processes of volatile trapping and release are temperature dependent over the temperature range relevant to Enceladus.

Carbon dioxide segregation in 1:4 and 1:9 CO 2:H 2O ices

The mid-infrared spectra of mixed vapor deposited ices of CO 2 and H 2O were studied as a function of both deposition temperature and warming from 15 to 100 K. The spectra of ices deposited at 15 K show marked changes on warming beginning at 60 K. These changes are consistent with CO 2 segregating within the ice matrix into pure CO 2 domains. Ices deposited at 60 and 70 K show a greater degree of segregation, as high as 90% for 1:4 CO 2:H 2O ice mixtures deposited at 70 K. As the ice is warmed above 80 K, preferential sublimation of the segregated CO 2 is observed. The kinetics of the segregation process is also examined. The segregation of the CO 2 as the ice is warmed corresponds to temperatures at which the structure of the water ice matrix changes from the high density amorphous phase to the low density amorphous phase. We show how these microstructural changes in the ice have a profound effect on the photochemistry induced by ultraviolet irradiation. These experimental results provide a framework in which observations of CO 2 on the icy bodies of the outer Solar System can be considered.

Characterization of lysozyme films produced by matrix assisted pulsed laser evaporation (MAPLE)

Thin lysozyme films of thickness up to more than 100 nm have been produced in a dry environment by MAPLE (matrix assisted pulsed laser evaporation) from a water ice matrix. Analysis of the films demonstrates that a significant part of the lysozyme molecules is transferred to the substrate without decomposition and that the protein activity is preserved. The film deposition rate for 1 wt% lysozyme has a maximum at 2 J/cm 2 of about 1 ng/cm 2 per laser shot. During the film production the deposition rate is constant without any sign of depletion or accumulation effects in the water ice target or in the growing film. Scanning electron microscopy (SEM) images demonstrate that the silicon substrate is completely covered by lysozyme films thicker than 100 nm. Deposition was also made from a target with pressed (100%) solid lysozyme, but the deposition was difficult to handle and with a much slower rate than that from a water ice matrix.

Production of active lysozyme films by matrix assisted pulsed laser evaporation at 355 nm

Thin lysozyme films have been produced in a dry environment by MAPLE (matrix assisted pulsed laser evaporation) from a water ice matrix irradiated by laser light at 355 nm above the absorption threshold of the protein. A significant part of the lysozyme molecules are transferred to the film without decomposition and the protein activity is preserved. The film deposition rate for 1 wt% lysozyme shows a clear maximum of about 1 ng/cm 2 per shot for a moderate fluence of 2 J/cm 2, which is about one-half of the deposition rate from a pressed (100%) lysozyme target.

Ultraviolet photolysis of amino acids in a 100 K water ice matrix: Application to the outer Solar System bodies

We report the rates of decomposition by ultraviolet (UV) photolysis of four amino acids in millimeter-thick crystalline water ice matrices at 100 K to constrain the survivability of these important organic molecules within ice lying near the surfaces of outer Solar System bodies. We UV-irradiated crystalline ice samples containing known concentrations of the amino acids glycine, aspartic acid, glutamic acid, and phenylalanine, then we measured the surviving concentrations using high performance liquid chromatography (HPLC) with fluorescence detection. From these experiments, we determine photolytic decomposition rates and half-lives. The half-life varies linearly with the ice thickness for all acids studied here. For example, glycine is the most resistant to photolytic destruction with a half-life of 50, 12, and 3.7 h in 1.6, 0.28, and 0.14 mm thick ices, respectively. We explain this linear variation of half-life with thickness as a consequence of extinction, mostly due to scattering, within these macroscopically thick ice samples. Applied to low latitude surface ice on Jupiter's satellite Europa, this analysis indicates that the concentration of any of these amino acids within the top meter of similar ice will be halved within a ∼10 year timescale.

Double Ionization of Quaterrylene (C40H20) in Water-Ice at 20 K with Lyα (121.6 nm) Radiation

Polycyclic aromatic hydrocarbon (PAH) molecules undergo facile ionization in cryogenic water-ices resulting in near quantitative conversions of neutral molecules to the corresponding singly charged radical cations. Here we report, for the first time, the production and stabilization of a doubly ionized, closed shell PAH in water-ice. The large PAH quaterrylene (QTR, C40H20) is readily photoionized and stabilized as QTR 2+ in a water-ice matrix at 20 K. The kinetic analysis of photolysis shows that the QTR 2+ is formed at the expense of QTR +, not directly from QTR. The long-axis polarized S1-S0 (1(1)B(3u) <-- 1(1)Ag) transition for QTR 2+ falls at 1.59 eV (782 nm). TD-DFT calculations at the B3LYP level predict that this transition falls at 1.85 eV (670 nm) for free gas-phase QTR 2+, within the 0.3 eV uncertainty associated with these calculations. This red shift of 0.26 eV is quite similar to the 0.24 eV red shift between the TD-DFT computational prediction for the lowest energy transition for QTR + (1.68 eV) and its value in a water matrix (1.44 eV). These results suggest that multiple photoionization of such large PAHs in water-ice can be an efficient process in general.

Laser-induced ion emission during polymer deposition from a flash-frozen water ice matrix

Flash-frozen water solutions of 1% weight PEG (polyethylene glycol) at −50 °C were used as targets at a laser wavelength of 355 nm for polymer deposition with Matrix-Assisted Pulsed Laser Evaporation (MAPLE). For medium laser fluences the transfer of PEG material to the substrate was accompanied by a pronounced ion flow from the matrix target which increases with fluence F as F 12. At the highest fluence the ion flow was partly attenuated, presumably due to plume shielding. Below a threshold of 3.5 J/cm 2 the PEG was deposited without any measurable ion emission from the target.

Infrared laser post-ionization of large biomolecules from an IR-MALD(I) plume

A two-infrared laser desorption/ionization method is described. A first laser, which was either an Er:YAG laser or an optical parametric oscillator (OPO), served for ablation/vaporization of small volumes of analyte/matrix sample at fluences below the ion detection threshold for direct matrix-assisted laser desorption/ionization mass spectrometry (MALDI-MS). A second IR-laser, whose beam intersected the expanding ablation plume at a variable distance and time delay, was used to generate biomolecular ions out of the matrix-assisted laser desorption (MALD) plume. Either one of the two above lasers or an Er:YSGG laser was used for post-ionization. Glycerol was used as IR-MALDI matrix, and mass spectra of peptides, proteins, as well as nucleic acids, some of which in excess of 10 5 u in molecular weight, were recorded with a time-of-flight mass spectrometer. A mass spectrum of cytochrome c from a water ice matrix is also presented. The MALD plume expansion was investigated by varying the position of the post-ionization laser beam above the glycerol sample surface and its delay time relative to the desorption laser. Comparison between the OPO (pulse duration, τ L = 6 ns) and the Er:YAG laser (τ L ∼120 ns) as primary excitation laser demonstrates a significant effect of the laser pulse duration on the MALD process.

Comparison of the effects of UV, H2O2/UV and gamma-irradiation processes on frozen and liquid water solutions of monochlorophenols.

The effects of UV irradiation, both in the presence and absence of hydrogen peroxide, as well as of gamma irradiation on 2- and 4-chlorophenol in a solid water ice matrix have been studied and compared to those effects known to occur in aqueous solutions. While UV photolysis (>280 nm) of monochlorophenols leads to efficient coupling reactions in ice and photosolvolysis products in liquid water; hydroxylation to chlorobenzenediols is the main pathway in the presence of H2O2 in both phases. The results show that the solute molecules accumulate in a layer surrounding the ice crystal walls during the freezing process, where they then react. The radiation chemistry of chlorophenol ice samples involves preferential coupling reactions at -78 degrees C rather than reactions with the OH radicals produced by cleavage of water molecules under the conditions employed (1 kGy h(-1)). The apparent similarities between the chemistry in the UV/H2O2-treated liquid and solid, and y-irradiated liquid and solid samples are discussed. It is suggested that the reactions of OH radicals within polycrystalline ice or snow are important natural processes that should be considered in environmental, ice-core or astrophysical research.