Long-timescale simulations of diffusion in molecular solids

Karssemeijer, Leendertjan; Pedersen, Andreas; Jónsson, Hannes; Cuppen, H. M.

doi:10.1039/c2cp41634d

Cited by 29 publications

(58 citation statements)

References 47 publications

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“…The large, correlated uncertainties prevent us from a confident extrapolation to lower temperatures, which would be more relevant to astrochemistry. The activation energy for diffusion for CO, 1.0 ± 1.5 kJ mol −1 , is in agreement with the value calculated by Karssemeijer et al (2012), 50 ± 1 meV or 4.8 ± 1 kJ mol −1 , or with a fraction to the value measured and calculated for CO-ice interaction (Manca et al 2001). The activation energy for diffusion of 12 ± 2 kJ mol −1 for H 2 CO is on the order of the magnitude of the energy required to break a hydrogen bond ( 10 kJ mol −1 ).…”

Section: Temperature Dependence Of the Diffusion Coefficientssupporting

confidence: 71%

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Mispelaer¹,

Theulé²,

Aouididi³

et al. 2013

A&A

115

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Context. Water is the major component of the interstellar ice mantle. In interstellar ice, chemical reactivity is limited by the diffusion of the reacting molecules, which are usually present at abundances of a few percent with respect to water. Aims. We want to study the thermal diffusion of H 2 CO, NH 3 , HNCO, and CO in amorphous water ice experimentally to account for the mobility of these molecules in the interstellar grain ice mantle. Methods. In laboratory experiments performed at fixed temperatures, the diffusion of molecules in ice analogues was monitored by Fourier transform infrared spectroscopy. Diffusion coefficients were extracted from isothermal experiments using Fick's second law of diffusion. Results. We measured the surface diffusion coefficients and their dependence with the temperature in porous amorphous ice for HNCO, H 2 CO, NH 3 , and CO. They range from 10 −15 to 10 −11 cm 2 s −1 for HNCO, H 2 CO, and NH 3 between 110 K and 140 K, and between 5-8 × 10 −13 cm 2 s −1 for CO between 35 K and 40 K. The bulk diffusion coefficients in compact amorphous ice are too low to be measured by our technique and a 10 −15 cm 2 s −1 upper limit can be estimated. The amorphous ice framework reorganization at low temperature is also put in evidence. Conclusions. Surface diffusion of molecular species in amorphous ice can be experimentally measured, while their bulk diffusion may be slower than the ice mantle desorption kinetics.

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Section: Temperature Dependence Of the Diffusion Coefficientssupporting

confidence: 71%

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Mispelaer¹,

Theulé²,

Aouididi³

et al. 2013

A&A

115

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“…This model was developed as a flexible version of the successful TIP4P/2005 potential, which gives a good description of the condensed phases of water (Abascal & Vega 2005;Vega & Abascal 2011). The H 2 O-CO potential as well as the CO intramolecular potential is described in Karssemeijer et al (2012). The intermolecular CO-CO potential is described below.…”

Section: Discussionmentioning

confidence: 99%

“…As explained in our previous paper (Karssemeijer et al 2012), an advantage of the KMC method is that, once the TOEs of a system are known for a specific temperature, one can easily adjust them for simulations at different temperatures without having to perform new transition-state searches. We therefore typically perform AKMC simulations of a system at a high temperature first, where states are easily discovered.…”

Section: Computational Detailsmentioning

confidence: 99%

“…The technique is implemented in the EON code 5 and is described in more detail in Karssemeijer et al (2012), which also demonstrates its applicability to molecular systems. In this section, we will only give a short summary of the AKMC method before proceeding to the simulations themselves and their results.…”

Section: Simulationsmentioning

confidence: 99%

“…In previous work, we have studied the mobility of CO on hexagonal water ice and found that, for this system, the diffusion barrier is equal to one-third of the binding energy (Karssemeijer et al 2012). In the present paper, we will apply the same methodology to determine the diffusion barriers of a more astrophysically relevant system: adsorbed CO on amorphous solid water (ASW).…”

Section: Introductionmentioning

confidence: 99%

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Dynamics of Co in Amorphous Water-Ice Environments

Karssemeijer

Ioppolo

Hemert

et al. 2013

ApJ

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The long-timescale behavior of adsorbed carbon monoxide on the surface of amorphous water ice is studied under dense cloud conditions by means of off-lattice, on-the-fly, kinetic Monte Carlo simulations. It is found that the CO mobility is strongly influenced by the morphology of the ice substrate. Nanopores on the surface provide strong binding sites, which can effectively immobilize the adsorbates at low coverage. As the coverage increases, these strong binding sites are gradually occupied leaving a number of admolecules with the ability to diffuse over the surface. Binding energies and the energy barrier for diffusion are extracted for various coverages. Additionally, the mobility of CO is determined from isothermal desorption experiments. Reasonable agreement on the diffusivity of CO is found with the simulations. Analysis of the 2152 cm −1 polar CO band supports the computational findings that the pores in the water ice provide the strongest binding sites and dominate diffusion at low temperatures.

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Grain Surface Models and Data for Astrochemistry

et al. 2017

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The cross-disciplinary field of astrochemistry exists to understand the formation, destruction, and survival of molecules in astrophysical environments. Molecules in space are synthesized via a large variety of gas-phase reactions, and reactions on dust-grain surfaces, where the surface acts as a catalyst. A broad consensus has been reached in the astrochemistry community on how to suitably treat gas-phase processes in models, and also on how to present the necessary reaction data in databases; however, no such consensus has yet been reached for grain-surface processes. A team of ∼25 experts covering observational, laboratory and theoretical (astro)chemistry met in summer of 2014 at the Lorentz Center in Leiden with the aim to provide solutions for this problem and to review the current state-of-the-art of grain surface models, both in terms of technical implementation into models as well as the most up-to-date information available from experiments and chemical computations. This review builds on the results of this workshop and gives an outlook for future directions.

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Long-timescale simulations of diffusion in molecular solids

Cited by 29 publications

References 47 publications

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Dynamics of Co in Amorphous Water-Ice Environments

Grain Surface Models and Data for Astrochemistry

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Long-timescale simulations of diffusion in molecular solids

Cited by 29 publications

References 47 publications

Diffusion measurements of CO, HNCO, H2CO, and NH3in amorphous water ice

Diffusion measurements of CO, HNCO, H2CO, and NH3in amorphous water ice

Dynamics of Co in Amorphous Water-Ice Environments

Grain Surface Models and Data for Astrochemistry

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Product

Resources

About

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice

Diffusion measurements of CO, HNCO, H₂CO, and NH₃in amorphous water ice