A Fast, Direct Procedure to Estimate the Desorption Energy for Various Molecular Ices of Astrophysical Interest

Luna, R.; Luna-Ferrándiz, Ramón; Millán, Carlos; Domingo, M.; Muñoz, G. M.; Santonja, C.; Satorre, M. Á.

doi:10.3847/1538-4357/aa7562

Cited by 12 publications

(9 citation statements)

References 14 publications

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“…The slow decrease in intensity of the TPD signal inferred from the QMS data collected during the three experiments suggests that these CO molecules are strongly bound to the different surfaces, with binding energies ranging between ∼1000 K and 1600 K. The binding energies of the molecules can be directly estimated from the maximum desorption temperature as described in Luna et al (2017), where E bin (in K)=30.9 × T des (in K).…”

Section: Resultsmentioning

confidence: 99%

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CO Depletion: A Microscopic Perspective

Cazaux

Martín-Doménech

Chen

et al. 2017

ApJ

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In regions where stars form, variations in density and temperature can cause gas to freeze out onto dust grains forming ice mantles, which influences the chemical composition of a cloud. The aim of this paper is to understand in detail the depletion (and desorption) of CO on (from) interstellar dust grains. Experimental simulations were performed under two different (astrophysically relevant) conditions. In parallel, Kinetic Monte Carlo simulations were used to mimic the experimental conditions. In our experiments, CO molecules accrete onto water ice at temperatures below 27 K, with a deposition rate that does not depend on the substrate temperature. During the warm-up phase, the desorption processes do exhibit subtle differences, indicating the presence of weakly bound CO molecules, therefore highlighting a low diffusion efficiency. IR measurements following the ice thickness during the TPD confirm that diffusion occurs at temperatures close to the desorption. Applied to astrophysical conditions, in a pre-stellar core, the binding energies of CO molecules, ranging between 300 and 850 K, depend on the conditions at which CO has been deposited. Because of this wide range of binding energies, the depletion of CO as a function of A V is much less important than initially thought. The weakly bound molecules, easily released into the gas phase through evaporation, change the balance between accretion and desorption, which result in a larger abundance of CO at high extinctions. In addition, weakly bound CO molecules are also more mobile, and this could increase the reactivity within interstellar ices.

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Section: Resultsmentioning

confidence: 99%

“…The binding energies of the molecules can be directly estimated from the maximum desorption temperature as described in Luna et al (2017), where E bin (in K) = 30.9×T des (in K).…”

Section: Resultsmentioning

confidence: 99%

CO Depletion: A Microscopic Perspective

Cazaux

Martín-Doménech

Chen

et al. 2017

ApJ

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“…The position of the arrows (corresponding to highest temperature desorption in CO:N 2 experiments) and the position of the vertical dashed lines (highest temperature desorption in pure ices desorption) were calculated using Eq. (12) of Luna et al (2017), which allows us to express the high-energy desorption values displayed in Tables 1 and 2 as temperatures in kelvins. It is evident that blue arrows (N 2 in CO-N 2 system) exhibit a considerable shift towards lower temperatures with respect to the blue dashed lines (pure N 2 experiments).…”

Section: Analysis and Discussionmentioning

confidence: 99%

Segregation effect and N₂ binding energy reduction in CO-N₂ systems adsorbed on water ice substrates

Nguyen

Baouche

Congiu

et al. 2018

A&A

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Context. CO and N2 are two abundant species in molecular clouds. CO molecules are heavily depleted from the gas phase towards the centre of pre-stellar cores, whereas N2 maintains a high gas phase abundance. For example, in the molecular cloud L183, CO is depleted by a factor of ≈400 in its centre with respect to the outer regions of the cloud, whereas N2 is only depleted by a factor of ≈20. The reason for this difference is not yet clear, since CO and N2 have identical masses, similar sticking properties, and a relatively close energy of adsorption. Aims. We present a study of the CO-N2 system in sub-monolayer regimes, with the aim to measure, analyse and elucidate how the adsorption energy of the two species varies with coverage, with much attention to the case where CO is more abundant than N2. Methods. Experiments were carried out using the ultra-high vacuum (UHV) set-up called VENUS. Sub-monolayers of either pure 13CO or pure 15N2 and 13CO:15N2 mixtures were deposited on compact amorphous solid water ice, and crystalline water ice. Temperature-programmed desorption experiments, monitored by mass spectrometry, are used to analyse the distributions of binding energies of 13CO and 15N2 when adsorbed together in different proportions. Results. The distribution of binding energies of pure species varies from 990 K to 1630 K for 13CO, and from 890 K to 1430 K for 15N2. When a CO:N2 mixture is deposited, the 15N2 binding energy distribution is strongly affected by the presence of 13CO, whereas the adsorption energy of CO is unaltered. Conclusions. Whatever types of water ice substrate we used, the N2 effective binding energy was significantly lowered by the presence of CO molecules. We discuss the possible impact of this finding in the context of pre-stellar cores.

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“…Martín-Doménech et al 2014;Fayolle et al 2016). However, for CO-dominated ices that appear late in the evolution of the cloud core, desorption energy and the associated binding energy (see below) can be notably lower, as indicated by thermal desorption of pure ices (Collings et al 2004;Luna et al 2017). This aspect was taken into account when comparing modelling results with observational data (Section 3.2).…”

Section: Chemical Reactions Networkmentioning

confidence: 99%

The efficiency of photodissociation for molecules in interstellar ices

Kalvāns

2018

Monthly Notices of the Royal Astronomical Society

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Processing by interstellar photons affects the composition of the icy mantles on interstellar grains. The rate of photodissociation in solids differs from that of molecules in the gas phase. The aim of this work was to determine an average, general ratio between photodissociation coefficients for molecules in ice and gas. A 1D astrochemical model was utilized to simulate the chemical composition for a line of sight through a collapsing interstellar cloud core, whose interstellar extinction changes with time. At different extinctions, the calculated column densities of icy carbon oxides and ammonia (relative to water ice) were compared to observations. The latter were taken from literature data of background stars sampling ices in molecular clouds. The bestfit value for the solid/gas photodissociation coefficient ratio was found to be ≈ 0.3. In other words, gas-phase photodissociation rate coefficients have to be reduced by a factor of 0.3 before applying them to icy species. A crucial part of the model is a proper inclusion of cosmic-ray induced desorption. Observations sampling gas with total extinctions in excess of ≈ 22 mag were found to be uncorrelated to modelling results, possibly because of grains being covered with non-polar molecules.

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A Fast, Direct Procedure to Estimate the Desorption Energy for Various Molecular Ices of Astrophysical Interest

Cited by 12 publications

References 14 publications

CO Depletion: A Microscopic Perspective

CO Depletion: A Microscopic Perspective

Segregation effect and N₂ binding energy reduction in CO-N₂ systems adsorbed on water ice substrates

The efficiency of photodissociation for molecules in interstellar ices

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A Fast, Direct Procedure to Estimate the Desorption Energy for Various Molecular Ices of Astrophysical Interest

Cited by 12 publications

References 14 publications

CO Depletion: A Microscopic Perspective

CO Depletion: A Microscopic Perspective

Segregation effect and N2 binding energy reduction in CO-N2 systems adsorbed on water ice substrates

The efficiency of photodissociation for molecules in interstellar ices

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Segregation effect and N₂ binding energy reduction in CO-N₂ systems adsorbed on water ice substrates