Cross Second Virial Coefficients and Dilute Gas Transport Properties of the Systems (N2+ C3H8), (C2H6+ C3H8), and (H2S + C3H8) from Ab Initio-Based Intermolecular Potentials

Hellmann, Robert

doi:10.1021/acs.jced.0c00605

“…Also shown in the figure as a densely packed dot-dash line is a 2020 correlation by Hellmann for CH 4 –N 2 derived from site–site fits to a detailed ab initio potential energy surface . The diffusion coefficients were calculated from the correlation given in the Supporting Information of Hellmann assuming an ideal gas at 101.325 kPa pressure and show an excellent agreement with the present data across the entire temperature range.…”

Section: Resultssupporting

confidence: 73%

“…Also shown in the figure as a densely packed dot-dash line is a 2020 correlation by Hellmann for CH 4 –N 2 derived from site–site fits to a detailed ab initio potential energy surface . The diffusion coefficients were calculated from the correlation given in the Supporting Information of Hellmann assuming an ideal gas at 101.325 kPa pressure and show an excellent agreement with the present data across the entire temperature range. We note that the ab initio correlation shows a slight difference from the present extrapolated values at high temperatures, and additional data for CH 4 at temperatures greater than reported in this work would be valuable.…”

Section: Resultssupporting

confidence: 73%

“…Dot-long dash lines are derived from Lennard-Jones parameters (see text for references), and the bold widely spaced dashed line that lies near the Lennard-Jones estimates for CH 4 is a molecular dynamics simulation from Chae et al , ref . The dense dot-dashed line for CH 4 –N 2 is a correlation from Hellmann derived from an ab initio potential energy surface calculated by Hellmann et al …”

Section: Resultsmentioning

confidence: 99%

“…The “twin tube” methodology was estimated to have a lower systematic uncertainty than the arrested flow technique, and these results were more consistent with the 1972 values of Marrero and Mason than the earlier work of Coward and Georgeson and later recommendation of Massman. In addition to the experimental measurements for CH 4 –N 2 , there exist various direct calculations of interest, including a 2020 correlation developed by Hellmann based on an ab initio potential energy surface and earlier values from Chae et al using molecular dynamics simulations.…”

Section: Introductionmentioning

confidence: 99%

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Binary Diffusion Coefficients for Methane and Fluoromethanes in Nitrogen

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¹

,

Manion

²

2021

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Binary gas-phase diffusion coefficients, of interest in physical models of atmospheric and combustion chemistry, have been measured in N2 for the homologous series of refrigerant-related (fluoro)methanes: methane (CH4), fluoromethane (CH3F), difluoromethane (CH2F2), and trifluoromethane (CHF3). Values have been determined by reverse-flow gas chromatography, which has been previously demonstrated to provide accurate results over a wide range of temperatures. Coefficients were measured at temperatures of (300–550) K for all species and extending up to 650 and 723 K for CH2F2 and CHF3, respectively, and down to 250 K for CH4. We also performed measurements for CH4 in air at temperatures of (250–350) K, obtaining values the same as in N2 within 0.3%, well within our experimental uncertainty. We report the first measurements for CH3F and compare with the limited literature data for the other compounds. Our results agree broadly with earlier measurements in both N2 and air. The greater temperature ranges reported in this work lead to temperature dependences that differ from most previous experiments, although they are consistent with several literature estimates and are similar to temperature exponents found for small hydrocarbons in N2. Comparison of the present work with a recent study that found different diffusion coefficients for methane when determined in a typical arrested flow apparatus and a novel “twin tube” method unaffected by sample adsorption shows a much better agreement with the arrested flow results over all common temperatures.

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“…Collisional exchange of energy (internal and kinetic) is a fundamental process leading to the equilibrium between internal temperatures of molecules and kinetic temperature of the gas in which they are immersed 1 . There exists many attempts to compute those rates for transport properties, all the way from classical computation (recent examples are 2,3 ) to full quantum ab initio computations 4 . While a large body of investigation deals with collisional rates for astrophysics and planetary science, as described in the next paragraph, the role of internal to kinetic energy exchanges is also crucial in cold molecules physics ( ∼ K to mK).…”

mentioning

confidence: 99%

Quantum nature of molecular vibrational quenching: Water - molecular hydrogen collisions

Wiesenfeld

2021

Preprint

0

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Rates of conversions of molecular internal energy to and from kinetic energy by means of molecular collision allows to compute collisional line shapes and transport properties of gases. Knowledge of ro-vibrational quenching rates is necessary to connect spectral observations to physical properties of warm astrophysical gasses, including exo-atmospheres. For a system of paramount importance in this context, the vibrational bending mode quenching of H 2 O by H 2 , we show here that exchange of vibrational to rotational and kinetic energy remains a quantum process, despite the large numbers of quantum levels involved and the large vibrational energy transfer. The excitation of the quantized rotor of the projectile is by far the most effective ro-vibrational quenching path of water. To do so, we use a fully quantum first principle computation, potential and dynamics, converging it at all stages, in a full coupled channel formalisms. We present here rates for the quenching of the first bending mode of ortho-H 2 O by ortho H 2 , up to 500 K, in a fully converged coupled channels formalism.

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Mutual Intersection Points of Reduced Collision Integrals for Lennard–Jones (n-m), Hulburt–Hirschfelder, and Tang–Toennies Potential Energy Functions

Hohm

¹

2022

Int J Thermophys

2

0

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We investigate the reduced collision integrals $$\Omega ^{(\ell ,s)*}(T^*)$$ Ω ( ℓ , s ) ∗ ( T ∗ ) for $$1 \le \ell \le 4$$ 1 ≤ ℓ ≤ 4 , $$\ell \le s \le 7$$ ℓ ≤ s ≤ 7 and $$\ell + s \le 8$$ ℓ + s ≤ 8 for several isotropic potential energy functions: the Lennard–Jones $$(n-m)$$ ( n - m ) , the Hulburt–Hirschfelder, and Tang–Toennies potential. It is observed that for a given $$\ell$$ ℓ and s, $$\Omega ^{(\ell ,s)*}(T^*)$$ Ω ( ℓ , s ) ∗ ( T ∗ ) shows a mutual intersection region at a reduced temperature $$0.39< T^*=T^*_{\ell s} < 2.22$$ 0.39 < T ∗ = T ℓ s ∗ < 2.22 which is nearly independent of the potential energy function used.

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Cross Second Virial Coefficients and Dilute Gas Transport Properties of the Systems (N₂+ C₃H₈), (C₂H₆+ C₃H₈), and (H₂S + C₃H₈) from Ab Initio-Based Intermolecular Potentials

Cited by 8 publications

References 61 publications

Binary Diffusion Coefficients for Methane and Fluoromethanes in Nitrogen

Binary Diffusion Coefficients for Methane and Fluoromethanes in Nitrogen

Quantum nature of molecular vibrational quenching: Water - molecular hydrogen collisions

Mutual Intersection Points of Reduced Collision Integrals for Lennard–Jones (n-m), Hulburt–Hirschfelder, and Tang–Toennies Potential Energy Functions

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