The structure and orientational disorder in solid <i>n</i>-butane by neutron powder diffraction

Refson, Keith; Pawley, G. S.

doi:10.1107/s010876818609804x

Cited by 29 publications

(21 citation statements)

References 12 publications

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“…A neutron quasielastic study of bulk liquid butane at 190 K reports a D r of 277ϫ10 9 /s. 24 Our measurements on monolayer butane extend only to 149 K, but a reasonable extrapolation to 190 K ͓using an Arrhenius fit to the data in Fig. 6͑c͔͒ results in a value of 125 ϫ10 9 /s, considerably less than the bulk value.…”

Section: B Above Meltingmentioning

confidence: 60%

“…For example, bulk butane has a high-temperature plastic phase in which the molecules are translationally ordered but rotate about their long axis. 24 Such a phase is apparently not observed for the butane monolayer, which showed no quasielastic scattering below T m . On the other hand, evidence of uniaxial rotation has been found below the melting point of two different monolayer phases of the shortest alkane, ethane ͓CH 3 CH 3 ͔, adsorbed on graphite.…”

Section: Quasielastic Scattering Models a Scattering Functionsmentioning

confidence: 96%

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Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

Herwig

Dai

et al. 1997

The Journal of Chemical Physics

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Quasielastic neutron scattering experiments and molecular dynamics ͑MD͒ simulations have been used to investigate molecular diffusive motion near the melting transition of monolayers of flexible rod-shaped molecules. The experiments were conducted on butane and hexane monolayers adsorbed on an exfoliated graphite substrate. For butane, quasielastic scattering broader than the experimental energy resolution width of 70 eV appears abruptly at the monolayer melting point of T m ϭ116 K, whereas, for the hexane monolayer, it appears 20 K below the melting transition (T m ϭ170 K). To facilitate comparison with experiment, quasielastic spectra calculated from the MD simulations were analyzed using the same models and fitting algorithms as for the neutron spectra. This combination of techniques gives a microscopic picture of the melting process in these two monolayers which is consistent with earlier neutron diffraction experiments. Butane melts abruptly to a liquid phase where the molecules in the trans conformation translationally diffuse while rotating about their center of mass. In the case of the hexane monolayer, the MD simulations show that the appearance of quasielastic scattering below T m coincides with transformation of some molecules from trans to gauche conformations. Furthermore, if gauche molecules are prevented from forming in the simulation, the calculated incoherent scattering function contains no quasielastic component below T m . Modeling of both the neutron and simulated hexane monolayer spectra below T m favors a plastic phase in which there is nearly isotropic rotational diffusion of the gauche molecules about their center of mass, but no translational diffusion. The elastic scattering observed above T m is consistent with the coexistence of solid monolayer clusters with a fluid phase, as predicted by the simulations. For T/T m у1.3, the elastic scattering vanishes from the neutron spectra where the simulation indicates the presence of a fluid phase alone. The qualitative similarities between the observed and simulated quasielastic spectra lend support to a previously proposed ''footprint reduction'' mechanism of melting in monolayers of flexible, rod-shaped molecules. © 1997 American Institute of Physics. ͓S0021-9606͑97͒50237-6͔

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Section: B Above Meltingmentioning

confidence: 60%

Section: Quasielastic Scattering Models a Scattering Functionsmentioning

confidence: 96%

Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

Herwig

Dai

et al. 1997

The Journal of Chemical Physics

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“…Accordingly, the absorption coefficient of this band was determined to be 3.1 × 10 −18 cm molecule −1 , resulting in the column density and the ice thickness of the five hydrocarbon components to be (7.5 ± 0.8) × 10 16 molecules cm −2 and 80 ± 9 nm, respectively (Refson & Pawley 1986). However, it is important to investigate the relative fraction of C1-C6 hydrocarbons in the ice mixture.…”

Section: Methodsmentioning

confidence: 99%

Abiotic Formation of Carboxylic Acids (Rcooh) in Interstellar and Solar System Model Ices

Kim

Kaiser

2010

ApJ

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The present laboratory study simulated the abiotic formation of carboxylic acids (RCOOH) in interstellar and solar system model ices of carbon dioxide (CO 2 )-hydrocarbon mix C n H 2n+2 (n = 1-6). The pristine model ices were irradiated at 10 K under contamination-free, ultrahigh vacuum conditions with energetic electrons generated in the track of galactic cosmic-ray particles. The chemical processing of the ices was monitored by a Fourier transform infrared spectrometer and a quadrupole mass spectrometer during the irradiation phase and subsequent warm-up phases on line and in situ in order to extract qualitative (carriers) and quantitative (rate constants and yields) information on the newly synthesized species. Carboxylic acids were identified to be the main carrier, together with carbon monoxide (CO) and a trace of formyl (HCO) and hydroxycarbonyl (HOCO) radicals at 10 K. The upper limit of acid column density at 10 K was estimated as much as (1.2 ± 0.1) × 10 17 molecules cm −2 at doses of 17 ± 2 eV molecule −1 , or the yield of 39% ± 4% from the initial column density of carbon dioxide. The temporal column density profiles of the products were then numerically fit using two independent kinetic schemes of reaction mechanisms. Finally, we transfer this laboratory simulation to star-forming regions of the interstellar medium, wherein cosmic-ray-induced processing of icy grains at temperatures as low as 10 K could contribute to the current level of chemical complexity as evidenced in astronomical observations and in extracts of carbonaceous meteorites.

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“…The solid molar volumes were determined from crystal structures available in the literature (Dulmage and Lipscomb, 1951;Dietrich et al, 1975;Simon and Peters, 1980;Refson and Pawley, 1986;Antson et al, 1987;Etters and Kuchta, 1989;McMullan et al, 1992;Craven et al, 1993). The CH 3 CN, HCN, C 4 H 10 and C 2 H 2 have a temperature dependent polymorphism.…”

Section: C2 Titan's Solids Molar Volumesmentioning

confidence: 99%

Dissolution on Titan and on Earth: Toward the age of Titan's karstic landscapes

et al. 2015

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Titan's polar surface is dotted with hundreds of lacustrine depressions. Based on the hypothesis that they are karstic in origin, we aim at determining the efficiency of surface dissolution as a landshaping process on Titan, in a comparative planetology perspective with the Earth as reference. Our approach is based on the calculation of solutional denudation rates and allow inference of formation timescales for topographic depressions developed by chemical erosion on both planetary bodies. The model depends on the solubility of solids in liquids, the density of solids and liquids, and the average annual net rainfall rates. We compute and compare the denudation rates of pure solid organics in liquid hydrocarbons and of minerals in liquid water over Titan and Earth timescales. We then investigate the denudation rates of a superficial organic layer in liquid methane over one Titan year. At this timescale, such a layer on Titan would behave like salts or carbonates on Earth depending on its composition, which means that dissolution processes would likely occur, but would be 30 times slower on Titan compared to the Earth due to the seasonality of precipitation. Assuming an average depth of 100 m for Titan's lacustrine depressions, these could have developed in a few tens of millions of years at polar latitudes higher than 70 • N and S, and a few hundreds of million years at lower polar latitudes. The ages determined are consistent with the youth of the surface (< 1 Gyr) and the repartition of dissolution-related landforms on Titan.

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The structure and orientational disorder in solid n-butane by neutron powder diffraction

Abstract: The structure of deuterated n-butane (C4H~o), Mr = 68, has been determined in its three crystalline forms by neutron powder diffraction with ,X = 2.980/~,.

Cited by 29 publications

References 12 publications

Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

Quasielastic neutron scattering and molecular dynamics simulation studies of the melting transition in butane and hexane monolayers adsorbed on graphite

Abiotic Formation of Carboxylic Acids (Rcooh) in Interstellar and Solar System Model Ices

Dissolution on Titan and on Earth: Toward the age of Titan's karstic landscapes

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