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To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2007.10.005 Byline: Robert Hodyss, Paul V. Johnson, Grazyna E. Orzechowska, Jay D. Goguen, Isik Kanik Keywords: Ices; Ices; IR spectroscopy; Satellites; surfaces; Photochemistry Abstract: The mid-infrared spectra of mixed vapor deposited ices of CO.sub.2 and H.sub.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.sub.2 segregating within the ice matrix into pure CO.sub.2 domains. Ices deposited at 60 and 70 K show a greater degree of segregation, as high as 90% for 1:4 CO.sub.2:H.sub.2O ice mixtures deposited at 70 K. As the ice is warmed above 80 K, preferential sublimation of the segregated CO.sub.2 is observed. The kinetics of the segregation process is also examined. The segregation of the CO.sub.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.sub.2 on the icy bodies of the outer Solar System can be considered. Author Affiliation: Jet Propulsion Laboratory, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA Article History: Received 25 June 2007; Revised 11 October 2007

To link to full-text access for this article, visit this link: http://dx.doi.org/10.1016/j.icarus.2006.10.018 Byline: Grazyna E. Orzechowska, Jay D. Goguen, Paul V. Johnson, Alexandre Tsapin, Isik Kanik Keywords: Ices; Exobiology; Organic chemistry; Satellites; surfaces; Europa Abstract: 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 [approximately equal to]10 year timescale. Author Affiliation: Jet Propulsion Laboratory, Mail Stop 183-601, California Institute of Technology, 4800 Oak Grove Drive, Pasadena, CA 91109-8099, USA Article History: Received 30 June 2006; Revised 1 September 2006

The dependence of organic acid generation by alkene ozonolysis on relative humidity, thermalized Criegee intermediate scavengers, and alkene structure is investigated. The results indicate that stabilized Criegee intermediates (SCI) and their reaction with water are minor contributors to acid formation in the atmosphere and suggest that many of the acids are formed directly.

Formation of C4 and smaller carboxylic acids from gas-phase ozonolysis of several alkenes under dry and humid conditions is investigated. A technique based on solid-phase microextraction (SPME) and gas chromatography/mass spectrometry is developed to quantify the acids, other products and applied it to the reactions of ozone with propene trans-2-butene, 2,3-dimethyl-2-butene and isoprene.

Sonication is a technique used by environmental engineers to monitor hazardous chemicals in aqeous systems using measuring equipment. It is often used to measure the amount of chlorinated hydrocarbons in water and determine the pH of water before and after sonication. Studies which applied sonication in their analysis revealed its great potential for predicting reactions, analyzing process conditions and developing ultrasound monitoring methods.

Photolysis of heptanal is investigated both experimentally and theoretically. Photoexcited heptanol undergoes rapid intersystem crossing to the triplet manifold and on the basis of combined experimental and theoretical evidence, the remaining heptanal photolysis proceeds to form an estimated 10% HCO hexyl radical and 30% cyclic alcohols.

Students should learn about application and theory of ultrasound, a technology useful in environmental studies. Sonication devices could be useful in the problem of chlorinated hydrocarbons at water treatment facilities. Carbon tetrachloride will degrade upon sonication in aqueous solution and is suitable for a student exercise. A pH change can be seen using indicators. Ultrasound is increasingly used in chemistry, medicine, and industry.

The dependence of organic acid generation by alkene ozonolysis on relative humidity, thermalized Criegee intermediate scavengers, and alkene structure is investigated. Carboxylic acids generated from the ozonolysis of 1-hexene, 1-octene, 1-decene, trans-3-octene, and 1-methylcyclohexene were analyzed as trimethylsilyl (TMS) derivatives. Experiments were performed under dry (relative humidity (RH) < 1%) and humid (RH = 65%) conditions with cyclohexane or n-butyl ether as an OH scavenger. Pentanoic acid is produced from 1-hexene and trans-3-octene with yields 8.5 ± 2.6 and 5.0 ± 1.5% under dry conditions and 5.1 ± 1.5 and 2.8 ± 0.8% under humid conditions, respectively. Heptanoic acid yields from 1-octene are 8.3 ± 2.5 and 4.4 ± 1.3% under dry and humid conditions, respectively. Ozonolysis of 1-methylcyclohexene produced six C5−C7 multifunctional carboxylic acids, with a total yield of 7%. Several other acids and aldehydes were also monitored and quantified. An additional set of experiments with added stabilized Criegee intermediate (SCI) scavengers was performed for 1-octene ozonolysis under dry conditions. The results indicate that SCIs and their reaction with water are minor contributors to acid formation in the atmosphere and suggest that many of the acids are formed directly. [ABSTRACT FROM AUTHOR]

Abstract: The mid-infrared spectra of mixed vapor deposited ices of CO2 and H2O 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 CO2 segregating within the ice matrix into pure CO2 domains. Ices deposited at 60 and 70 K show a greater degree of segregation, as high as 90% for 1:4 CO2:H2O ice mixtures deposited at 70 K. As the ice is warmed above 80 K, preferential sublimation of the segregated CO2 is observed. The kinetics of the segregation process is also examined. The segregation of the CO2 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 CO2 on the icy bodies of the outer Solar System can be considered. [Copyright &y& Elsevier]