Diffusion and infrared properties of molecules in ice mantles

Within dense molecular clouds the formation of frozen icy mantles on interstellar dust grains is thought to be the result of various growth conditions. The molecules, which make up the ice mantles are probably completely mixed. To study the physical properties of such ice mixtures the experiments were performed on the evaporation processes and on the spectroscopic properties of CO, CO2, and CH4 in water rich ices. The decrease in concentration of volatile molecules in ice samples deposited at 10 K and subsequently heated is found to occur essentially in two steps. The first one, corresponding to an evaporation of part of the volatile molecules, starts at about 25 K for CO, 32 K for CH4, and 70 K for CO2. During the crystallization of H2O ice at temperatures greater than 120 K a second evaporation occurs leading to the complete disappearance of the volatile molecules in the solid phase. The main astrophysical implications of the diffusion and spectroscopic behaviors are presented. The possible effects of a heating source on the fraction of volatile molecules, such as CO trapped in grain mantles, are discussed

New insights in the photochemistry of grain mantles: The identification of the 4.62 and 6.87 micron bands

The mid-IR spectral region of molecular clouds is known to show the fingerprints of molecules frozen in the icy mantles of the interstellar grains. To study the complex chemical and physical interactions on the ice mantles accreted on grains in molecular clouds numerous UV irradiation and diffusion experiments were performed. The irradiation of binary ices was studied. Using isotopic labelling on NH3/CO and NH3/O2 ices numerous compounds were identified, of which OCN(-), NO2(-), NO3(-), and NH4(+) ions reveal a new type of chemical reactions. It appeared that these compounds were formed by proton transfer reactions induced by the interaction between an acid (HNCO, HNO2, HNO3) and a base (NH3) through a hydrogen bond. This mechanism was confirmed by a study of photolyzed diluted argon mixtures. The main astrophysically relevant data from the overall study are presented. The 4.62 micron band in W33A can be reproduced with NH3/CO containing irradiated ices and was identified with OCN(-). The 6.87 micron band in W33A and other photostellar objects is reproduced with NH3/O2 containing ices and is identified with NH4(+)

Ions in grain mantles - A new explanation for the 6.86 micron absorption in W33A

Wetensch. publicatieFaculteit der Wiskunde en Natuurwetenschappe

Modelling the impact of toxic and disturbance stress on white-tailed eagle (Haliaeetus albicilla) populations

Several studies have related breeding success and survival of sea eagles to toxic or non-toxic stress separately. In the present investigation, we analysed single and combined impacts of both toxic and disturbance stress on populations of white-tailed eagle (Haliaeetus albicilla), using an analytical single-species model. Chemical and eco(toxico)logical data reported from laboratory and field studies were used to parameterise and validate the model. The model was applied to assess the impact of ∑PCB, DDE and disturbance stress on the white-tailed eagle population in The Netherlands. Disturbance stress was incorporated through a 1.6% reduction in survival and a 10–50% reduction in reproduction. ∑PCB contamination from 1950 up to 1987 was found to be too high to allow the return of white-tailed eagle as a breeding species in that period. ∑PCB and population trends simulated for 2006–2050 suggest that future population growth is still reduced. Disturbance stress resulted in a reduced population development. The combination of both toxic and disturbance stress varied from a slower population development to a catastrophical reduction in population size, where the main cause was attributed to the reduction in reproduction of 50%. Application of the model was restricted by the current lack of quantitative dose–response relationships between non-toxic stress and survival and reproduction. Nevertheless, the model provides a first step towards integrating and quantifying the impacts of multiple stressors on white-tailed eagle populations