Infrared reflectance spectroscopy on thin films: Interference effects

Teolis, B. D.; Loeffler, M. J.; Raut, U.; Famá, M.; Baragiola, R. A.

doi:10.1016/j.icarus.2007.03.023

Cited by 60 publications

(62 citation statements)

References 31 publications

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“…In addition, the results discussed in the present paper are all in a regime where the proportionality relation (Teolis et al 2007) still holds (<3 × 10 16 molecules cm −2 ). The CO band shape can change when molecules other than CO are formed.…”

Section: A Sample Experimentssupporting

confidence: 57%

Hydrogenation reactions in interstellar CO ice analogues

Fuchs¹,

Cuppen²,

Ioppolo³

et al. 2009

A&A

417

517

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Context. Hydrogenation reactions of CO in inter-and circumstellar ices are regarded as an important starting point in the formation of more complex species. Previous laboratory measurements by two groups of the hydrogenation of CO ices provided controversial results about the formation rate of methanol. Aims. Our aim is to resolve this controversy by an independent investigation of the reaction scheme for a range of H-atom fluxes and different ice temperatures and thicknesses. To fully understand the laboratory data, the results are interpreted theoretically by means of continuous-time, random-walk Monte Carlo simulations. Methods. Reaction rates are determined by using a state-of-the-art ultra high vacuum experimental setup to bombard an interstellar CO ice analog with H atoms at room temperature. The reaction of CO + H into H 2 CO and subsequently CH 3 OH is monitored by a Fourier transform infrared spectrometer in a reflection absorption mode. In addition, after each completed measurement, a temperature programmed desorption experiment is performed to identify the produced species according to their mass spectra and to determine their abundance. Different H-atom fluxes, morphologies, and ice thicknesses are tested. The experimental results are interpreted using Monte Carlo simulations. This technique takes into account the layered structure of CO ice. Results. The formation of both formaldehyde and methanol via CO hydrogenation is confirmed at low temperature (T = 12−20 K). We confirm that the discrepancy between the two Japanese studies is caused mainly by a difference in the applied hydrogen atom flux, as proposed by Hidaka and coworkers. The production rate of formaldehyde is found to decrease and the penetration column to increase with temperature. Temperature-dependent reaction barriers and diffusion rates are inferred using a Monte Carlo physical chemical model. The model is extended to interstellar conditions to compare with observational H 2 CO/CH 3 OH data.

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Section: A Sample Experimentssupporting

confidence: 57%

Hydrogenation reactions in interstellar CO ice analogues

Fuchs¹,

Cuppen²,

Ioppolo³

et al. 2009

A&A

417

517

View full text Add to dashboard Cite

show abstract

“…This equation can, however, only be used for thin ice layers. Teolis et al 29 showed that the proportionality between the optical depth and the ice abundance breaks down for thicker layers (∼20 ML onwards); the integrated band area oscillates as a function of the layer thickness due to optical interference that is caused by the reflection at both the film-vacuum and film-substrate interfaces.…”

Section: Discussionmentioning

confidence: 99%

SURFRESIDE2: An ultrahigh vacuum system for the investigation of surface reaction routes of interstellar interest

Ioppolo

Fedoseev

Lamberts

et al. 2013

Review of Scientific Instruments

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A new ultrahigh vacuum experiment is described to study atom and radical addition reactions in interstellar ice analogues for astronomically relevant temperatures. The new setup -SURFace REaction SImulation DEvice (SURFRESIDE 2 ) -allows a systematic investigation of solid state pathways resulting in the formation of molecules of astrophysical interest. The implementation of a double beam line makes it possible to expose deposited ice molecules to different atoms and/or radicals sequentially or at the same time. Special efforts are made to perform experiments under fully controlled laboratory conditions, including precise atom flux determinations, in order to characterize reaction channels quantitatively. In this way, we can compare and combine different surface reaction channels with the aim to unravel the solid state processes at play in space. Results are constrained in situ by means of a Fourier transform infrared spectrometer and a quadrupole mass spectrometer using reflection absorption infrared spectroscopy and temperature programmed desorption, respectively. The performance of the new setup is demonstrated on the example of carbon dioxide formation by comparing the efficiency through two different solid state channels (CO + OH → CO 2 + H and CO + O → CO 2 ) for which different addition products are needed. The potential of SURFRESIDE 2 to study complex molecule formation, including nitrogen containing (prebiotic) compounds, is discussed.

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“…The value of band strength depends on multiple factors, such as the geometry (reflectance versus transmission) of the apparatus and the refractive index and thickness of the particular mixture considered in the experiments (Teolis et al 2007). Therefore, using band strengths published for different (or even similar) mixtures or optical configuration can introduce large errors in estimating the synthesized amount of CO 2 .…”

Section: Experimental Methodsmentioning

confidence: 99%

“…Therefore, using band strengths published for different (or even similar) mixtures or optical configuration can introduce large errors in estimating the synthesized amount of CO 2 . We instead generated synthetic spectra using Fresnel's equations for a film whose optical constants (n, k) are derived using the Lorentz-Lorenz equation and the published optical constants for the different species that constitute the film (Teolis et al 2007). The fraction of each component is adjusted to obtain the best match between the theoretical and the experimental spectra.…”

Section: Experimental Methodsmentioning

confidence: 99%

Photosynthesis of Carbon Dioxide From Carbon Surfaces Coated With Oxygen: Implications for Interstellar Molecular Clouds and the Outer Solar System

Fulvio

Raut

Baragiola

2012

ApJ

Self Cite

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We investigate via infrared spectroscopy the synthesis of CO 2 by ultraviolet irradiation (6.41 eV) of amorphous carbon covered with solid O 2 at 21 K. Oxidation occurs at the O 2 -carbon interface promoted by photon excitation or dissociation of O 2 molecules. The CO 2 production is linear with photon fluence with a yield of 3.3 ± 0.3 × 10 −5 CO 2 photon −1 ; the yield does not decrease at high fluences (at least up to 2 × 10 19 photons cm −2 ) since CO 2 is not photodissociated at this photon energy. Replacing oxygen with water ice did not produce CO 2 since H 2 O does not dissociate at this photon energy. The CO 2 synthesis process discussed in this Letter does not require H 2 O or CO and may be important in cold astrophysical environments where O 2 could be locally segregated on carbonaceous grains, such as in molecular clouds and icy objects in the outer solar system.

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Infrared reflectance spectroscopy on thin films: Interference effects

Cited by 60 publications

References 31 publications

Hydrogenation reactions in interstellar CO ice analogues

Hydrogenation reactions in interstellar CO ice analogues

SURFRESIDE2: An ultrahigh vacuum system for the investigation of surface reaction routes of interstellar interest

Photosynthesis of Carbon Dioxide From Carbon Surfaces Coated With Oxygen: Implications for Interstellar Molecular Clouds and the Outer Solar System

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