MD simulations of He evaporating from dodecane

Williams, Mark A.; Koehler, Sven P. K.

doi:10.1016/j.cplett.2015.04.008

Cited by 8 publications

(10 citation statements)

References 26 publications

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“…As discussed previously, we believe that the shift to higher kinetic energies for He is due to the cone mechanism; in the cone mechanism, a He atom finds itself in a cone-shaped opening/crater within the liquid surface but below the Gibbs dividing surface. As it is repelled by the surrounding alkyl chains, it is accelerated to the opening of the cone and expelled from the liquid with a higher kinetic energy, and preferentially along the surface normal . This occurs only to a small fraction of the He atoms and could in principle happen to any evaporating particle.…”

Section: Resultsmentioning

confidence: 99%

“…We employed the all-atom 1995 release of the AMBER force field (ref ) as done in our previous work (ref ) for the MD simulations of dodecane. As a general-purpose force field, AMBER has successfully been used for modeling liquids and also well-reproduced the bulk density of our liquid when compared to other force fields.…”

Section: Methodsmentioning

confidence: 99%

“…These computational studies had been motivated by experimental work by Nathanson and co-workers, who had measured the kinetic energy distribution of He from liquid dodecane microjets under vacuum using time-of-flight methods . Both studies qualitatively agree that the He atom kinetic energy distribution is non-Maxwellian with an average kinetic energy of (1.14 ± 0.01) × 2 RT (experimental, ref ) and (1.05 ± 0.03) × 2 RT (theory, ref , but (1.08 ± 0.03) × 2 RT after correction for the round cross section of the molecular beam used in the experiments). Obtaining these kinetic energy distributions experimentally is a major advance as it is generally very challenging to measure any dynamics at liquid surfaces as their high vapor pressure makes working under rarified vacuum conditions almost impossible.…”

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

“…In a recent publication, we have reported the kinetic energy distribution of He atoms evaporating from liquid dodecane (C 12 H 26 ) obtained by molecular dynamics (MD) simulations. 1 These computational studies had been motivated by experimental work by Nathanson and co-workers, who had measured the kinetic energy distribution of He from liquid dodecane microjets under vacuum using time-of-flight methods. 2 Both studies qualitatively agree that the He atom kinetic energy distribution is non-Maxwellian with an average kinetic energy of (1.14 ± 0.01) × 2RT (experimental, ref 2) and (1.05 ± 0.03) × 2RT (theory, ref 1, but (1.08 ± 0.03) × 2RT after correction for the round cross section of the molecular beam used in the experiments).…”

Section: ■ Introductionmentioning

confidence: 99%

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Kinetic Energy and Angular Distributions of He and Ar Atoms Evaporating from Liquid Dodecane

Patel¹,

Williams²,

Koehler

2016

J. Phys. Chem. B

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Abstract:We report both kinetic energy and angular distributions for He and Ar atoms evaporating from C 12 H 26 . All result were obtained by performing molecular dynamics simulations of liquid C 12 H 26 with around 10-20 noble gas atoms dissolved in the liquid, and by subsequently following the trajectories of the noble gas atoms after evaporation from the liquid. While He evaporates with a kinetic energy distribution of (1.05±0.03) × 2RT (corrected for the geometry used in experiments: (1.08±0.03) × 2RT, experimentally obtained value: (1.14±0.01) × 2RT), Ar displays a kinetic energy distribution that better matches a Maxwell-Boltzmann distribution at the temperature of the liquid ((0.99±0.04) × 2RT). This behavior is also reflected in the angular distributions which are close to a cosine distribution for Ar, but slightly narrower -especially for faster atoms -in the case of He. This behavior of He is most likely due to the weak interaction potential between He and the liquid hydrocarbon.2

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Section: Resultsmentioning

confidence: 99%

Section: Methodsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 92%

Section: Introductionmentioning

confidence: 99%

Section: ■ Introductionmentioning

confidence: 99%

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Kinetic Energy and Angular Distributions of He and Ar Atoms Evaporating from Liquid Dodecane

Patel¹,

Williams²,

Koehler

2016

J. Phys. Chem. B

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Molecular beam scattering from flat jets of liquid dodecane and water

Yang,

Foreman,

Saric

et al. 2024

Natural Sciences

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Molecular beam experiments in which gas molecules are scattered from liquids provide detailed, microscopic perspectives on the gas–liquid interface. Extending these methods to volatile liquids while maintaining the ability to measure product energy and angular distributions presents a significant challenge. The incorporation of flat liquid jets into molecular beam scattering experiments in our laboratory has allowed us to demonstrate their utility in uncovering dynamics in this complex chemical environment. Here, we summarize recent work on the evaporation and scattering of Ne, CD4, ND3, and D2O from a dodecane flat liquid jet and present first results on the evaporation and scattering of Ar from a cold salty water jet. In the evaporation experiments, Maxwell–Boltzmann flux distributions with a cosθ angular distribution are observed. Scattering experiments reveal both impulsive scattering (IS) and trapping followed by thermal desorption (TD). Super‐specular scattering is observed for all four species scattered from dodecane and is attributed to anisotropic momentum transfer to the liquid surface. In the IS channel, rotational excitation of the polyatomic scatterers is a significant energy sink, and these species accommodate more readily on the dodecane surface compared to Ne. Our preliminary results on cold salty water jets suggest that Ar atoms undergo some vapor‐phase collisions when evaporating from the liquid surface. Initial scattering experiments characterize the mechanisms of Ar interacting with an aqueous jet, allowing for comparison to dodecane systems.Key Points Molecular beam scattering from flat liquid jets is a powerful technique to elucidate mechanistic detail at the gas–liquid interface. Previous dodecane scattering experiments have uncovered angularly‐resolved thermal desorption fractions and energy transfer at the interface for several small molecule scatterers. Preliminary results on scattering from cold salty water reveal mechanisms of interaction between argon and an aqueous jet.

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When Liquid Rays Become Gas Rays: Can Evaporation Ever Be Non-Maxwellian?

Nathanson

2021

Molecular Beams in Physics and Chemistry

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A rare mistake by Otto Stern led to a confusion between density and flux in his first measurement of a Maxwellian speed distribution. This error reveals the key role of speed itself in Stern’s development of “the method of molecular rays”. What if the gas-phase speed distributions are not Maxwellian to begin with? The molecular beam technique so beautifully advanced by Stern can also be used to explore the speed distribution of gases evaporating from liquid microjets, a tool developed by Manfred Faubel. We employ liquid water and alkane microjets containing dissolved helium atoms to monitor the speed of evaporating He atoms into vacuum. While most dissolved gases evaporate in Maxwellian speed distributions, the He evaporation flux is super-Maxwellian, with energies up to 70% higher than the flux-weighted average energy of 2 RTliq. The explanation of this high-energy evaporation involves two beautiful concepts in physical chemistry: detailed balancing between He atom evaporation and condensation (starting with gas-surface collisions) and the potential of mean force on the He atom (starting with He atoms just below the surface). We hope that these measurements continue to fulfill Stern’s dream of the “directness and simplicity of the molecular ray method.”

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MD simulations of He evaporating from dodecane

Cited by 8 publications

References 26 publications

Kinetic Energy and Angular Distributions of He and Ar Atoms Evaporating from Liquid Dodecane

Kinetic Energy and Angular Distributions of He and Ar Atoms Evaporating from Liquid Dodecane

Molecular beam scattering from flat jets of liquid dodecane and water

When Liquid Rays Become Gas Rays: Can Evaporation Ever Be Non-Maxwellian?

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