Laboratory studies of thermally processed H_2O-CH_3OH-CO_2 ice mixtures and their astrophysical implications (original) (raw)
Related papers
Arxiv preprint astro-ph/ …, 1994
Infrared spectroscopic observations toward objects obscured by dense cloud material show that H 2 O, CO and, likely, CO 2 are important constituents of interstellar ice mantles. In order to accurately calculate the column densities of these molecules, it is important to have good measurements of their infrared band strengths in astrophysical ice analogs. We present the results of laboratory experiments to determine these band strengths. Improved experimental methods, relying on simultaneous independent depositions of the molecule to be studied and of the dominating ice component, have led to accuracies better than a few percent. Furthermore, the temperature behavior of the infrared band strengths of CO and H 2 O are studied. In contrast with previous work, the strengths of the CO, CO 2 , and H 2 O infrared features are found to depend only weakly on the composition of the ice matrix, and the reversible temperature dependence of the CO band is found to be weaker than previously measured for a mixture of CO in H 2 O.
Observations of Solid Carbon Dioxide in Molecular Clouds with theInfrared Space Observatory
The Astrophysical Journal, 1999
Spectra of interstellar ice absorption features at a resolving power of j/*j B 1500È2000 are pre-CO 2 sented for 14 lines of sight. The observations were made with the Short-Wavelength Spectrometer (SWS) of the Infrared Space Observatory (ISO). Spectral coverage includes the primary stretching mode of CO 2 near 4.27 km in all sources ; the bending mode near 15.2 km is also detected in 12 of them. The selected sources include massive protostars (Elias 29 [in o Oph], GL 490, GL 2136, GL 2591, GL 4176, NGC 7538 IRS 1, NGC 7538 IRS 9, S140, W3 IRS 5, and W33 A), sources associated with the Galactic Center (Sgr A*, GCS 3 I, and GCS 4), and a background star behind a quiescent dark cloud in Taurus (Elias 16) ; they thus probe a diverse range of environments. Column densities of interstellar ice relative to CO 2 ice fall in the range 10%È23% : this ratio displays remarkably little variation for such a physically H 2 O diverse sample. Comparison of the observed proÐles with laboratory data for ice mixtures CO 2-bearing indicates that generally exists in at least two phases, one polar dominant) and one nonpolar CO 2 (H 2 O dominant). The observed proÐles may also be reproduced when the nonpolar components are (CO 2 CO 2 replaced with thermally annealed ices. Formation and evolutionary scenarios for and implications CO 2 for grain mantle chemistry are discussed. Our results support the conclusion that thermal annealing, rather than energetic processing due to UV photons or cosmic rays, dominates the evolution of CO 2 ices. bearing Subject headings : dust, extinction È infrared : ISM : lines and bands È ISM : molecules È stars : preÈmain-sequence 1 Based on observations with the Infrared Space Observatory, an ESA project with instruments funded by ESA Member States (especially the PI countries : France, Germany, the Netherlands, and the United Kingdom) and with the participation of ISAS and NASA.
Infrared Spectra and Thermodynamic Properties of Co 2 /Methanol Ices
The Astrophysical Journal, 2008
Ices of mixtures of carbon dioxide and methanol have been studied in a range of temperatures relevant for starforming regions, comets, polar caps of planets and satellites, and other solar system bodies. We have performed temperature-programmed desorption measurements and recorded IR spectra of various types of samples. The presence of two slightly different structures of CO 2 is manifest. A distorted CO 2 structure is characterized by bandshifts between 5 cm −1 (ν 3) and 10 cm −1 (ν 2) with respect to normal CO 2. If the samples are heated above 130 K, the distorted CO 2 sublimates and only the normal structure remains. The latter can stay trapped until the sublimation of crystalline methanol (150 K). The desorption energy (E d ∼ 20 kJ mol −1) of CO 2 from methanol ice, and the specific adsorption surface area (6 m 2 g −1) of amorphous CH 3 OH ice, have been determined. CO 2 does not penetrate into crystalline ice. Whereas the desorption energy is similar to that of CO 2 /H 2 O samples, the specific surface of methanol is much smaller than that of amorphous solid water (ASW). The interaction of CO 2 molecules with water and methanol is similar but ices of CH 3 OH are much less porous than ASW. The inclusion of CO 2 into previously formed ices containing these two species would take place preferentially into ASW. However, in processes of simultaneous deposition, methanol ice can admit a larger amount of CO 2 than water ice. CO 2 /CH 3 OH ices formed by simultaneous deposition admit two orders of magnitude more CO 2 than sequentially deposited ices. These findings can have direct relevance to the interpretation of observations from protostellar environments (e.g., RAFGL7009S) and comet nuclei.
Band profiles and band strengths in mixed H 2 O:CO ices
Astronomy and Astrophysics, 2007
Context. Laboratory spectroscopic research plays a key role in the identification and analysis of interstellar ices and their structure. To date, a number of molecules have been positively identified in interstellar ices, either as pure, mixed or layered ice structures.
The Nature of Carbon Dioxide Bearing Ices in Quiescent Molecular Clouds
The Astrophysical Journal, 2009
The properties of the ices that form in dense molecular clouds represent an important set of initial conditions in the evolution of interstellar and preplanetary matter in regions of active star formation. Of the various spectral features available for study, the bending mode of solid CO 2 near 15 µm has proven to be a particularly sensitive probe of physical conditions, especially temperature. We present new observations of this absorption feature in the spectrum of Q21-1, a background field star located behind a dark filament in the Cocoon Nebula (IC 5146). We show the profile of the feature be consistent with a two-component (polar + nonpolar) model for the ices, based on spectra of laboratory analogs with temperatures in the range 10-20 K. The polar component accounts for ∼ 85% of the CO 2 in the line of sight. We compare for the first time 15 µm profiles in three widely separated dark clouds (Taurus, Serpens and IC 5146), and show that they are indistinguishable to within observational scatter. Systematic differences in the observed CO 2 /H 2 O ratio in the three clouds have little or no effect on the 15 µm profile.
ISO observations of interstellar ices
Advances in Space Research, 1998
The first spectroscopic results horn IS0 (Infrared Space Observatory, have revealed a wealth of interesting features and in particular absorption signatures of a wide variety of solid state molecular species. We present here some new IS0 data obtained with SWS (Short Wavelength Spectrometer) toward the young deeply embedded object associated with RAFGL 7009s. Signatures of H20, CO, CO2 ices can be readily identified but also some much less abundant species such as 13C02, HzCO and CH4, all occurring in the near and mid-infrared region between 3 and 16 pm. The detection of CO2 at 4.27 and 15.2 pm confirms its presence in the IRAS-LRS spectra of several heavily absorbed sources. The very high extinction toward RAFGL 7009s makes it an excellent case to study other weak solid state absorption features, commonly measured in laboratory experiments. 01998 COSPAR. Published by Elsevier Science Ltd.
Infrared spectra and optical constants of astronomical ices: I. Amorphous and crystalline acetylene
Icarus, 2014
Here we report recent measurements on acetylene (C 2 H 2) ices at temperatures applicable to the outer Solar System and the interstellar medium. New near-and mid-infrared data, including optical constants (n, k), absorption coefficients (a), and absolute band strengths (A), are presented for both amorphous and crystalline phases of C 2 H 2 that exist below 70 K. Comparisons are made to earlier work. Electronic versions of the data are made available, as is a computer routine to use our reported n and k values to simulate the observed IR spectra. Suggestions are given for the use of the data and a comparison to a spectrum of Makemake is made.
Astrophysical Journal, 2008
With the goal to study the physical and chemical evolution of ices in solar-mass systems, a spectral survey is conducted of a sample of 41 low luminosity YSOs using 3-38 um Spitzer and ground-based spectra. The long-known 6.0 and 6.85 um bands are detected toward all sources, with the Class 0-type YSOs showing the deepest bands ever observed. In almost all sources the 6.0 um band is deeper than expected from the bending mode of pure solid H2O. The depth and shape variations of the remaining 5-7 um absorption indicate that it consists of 5 independent components, which, by comparison to laboratory studies, must be from at least 8 different carriers. Simple species are responsible for much of the absorption in the 5-7 um region, at abundances of 1-30% for CH3OH, 3-8% for NH3, 1-5% for HCOOH, ~6% for H2CO, and ~0.3% for HCOO- with respect to solid H2O. The 6.85 um band likely consists of one or two carriers, of which one is less volatile than H2O because its abundance relative to H2O is enhanced at lower H2O/tau_9.7 ratios. It does not survive in the diffuse interstellar medium (ISM), however. The similarity of the 6.85 um bands for YSOs and background stars indicates that its carrier(s) must be formed early in the molecular cloud evolution. If an NH4+ salt is the carrier its abundance with respect to solid H2O is typically 7%, and low temperature acid-base chemistry or cosmic ray induced reactions must have been involved in its formation. Possible origins are discussed for the carrier of an enigmatic, very broad absorption between 5 and 8 um. Finally, all the phenomena observed for ices toward massive YSOs are also observed toward low mass YSOs, indicating that processing of the ices by internal ultraviolet radiation fields is a minor factor in the early chemical evolution of the ices. [abridged]
IR spectral fingerprint of carbon monoxide in interstellar water–ice models
Monthly Notices of the Royal Astronomical Society
Carbon monoxide (CO) is the second most abundant molecule in the gas phase of the interstellar medium. In dense molecular clouds, it is also present in the solid phase as a constituent of the mixed water-dominated ices covering dust grains. Its presence in the solid phase is inferred from its infrared (IR) signals. In experimental observations of solid CO/water mixed samples, its IR frequency splits into two components, giving rise to a blue-and redshifted band. However, in astronomical observations, the former has never been observed. Several attempts have been carried out to explain this peculiar behaviour, but the question still remains open. In this work, we resorted to pure quantum mechanical simulations in order to shed some light on this problem. We adopted different periodic models simulating the CO/H 2 O ice system, such as single and multiple CO adsorption on water-ice surfaces, CO entrapped into water cages, and proper CO:H 2 O mixed ices. We also simulated pure solid CO. The detailed analysis of our data revealed how the quadrupolar character of CO and the dispersive forces with water ice determine the energetic of the CO/H 2 O ice interaction, as well as the CO spectroscopic behaviour. Our data suggest that the blueshifted peak can be assigned to CO interacting via the C atom with dangling H atoms of the water ice, while the redshifted one can actually be the result of CO involved in different reciprocal interactions with the water matrix. We also provide a possible explanation for the lack of the blueshifted peak in astronomical spectra. Our aim is not to provide a full account of the various interstellar ices, but rather to elucidate the sensitivity of the CO spectral features to different water-ice environments.
Astronomy and …, 1999
Results from groundbased observations and the Infrared Space Observatory (ISO) indicate that CH 3 OH, NH 3 and CH 4 are important constituents of interstellar ice mantles. In order to accurately calculate the column densities of these molecules, it is important to have good measurements of their infrared band strength in astrophysical ice analogs. Band strength measurements of CH 3 OH and CH 4 are presented showing that they depend only weakly on the composition of the ice matrix and the temperature. On the other hand, the umbrella mode of NH 3 does show a significant decrease when dilluted in H 2 O ice. For this reason the original estimates of the abundance of NH 3 in interstellar ice need to be revised upward by 30%.