Search

The infinite order sudden (IOS) treatment of the dynamics that yields the necessary collision integrals for the calculation of transport coefficients is tested for a gaseous mixture that includes a nonlinear polyatomic partner, the methane molecule, interacting with He. The use of a fully anisotropic potential obtained before from crossed beam experiments is shown to provide rather good agreement with the available experiments for diffusion and viscosity coefficients over a broad range of temperatures. The comparison with more accurate calculations already carried out by us also shows extremely good agreement between the IOS calculations and the earlier, much more costly, evaluation through a quantum coupled states dynamics. The present calculations therefore indicate that, even for a more complicated nonlinear molecular partner in the mixture, IOS results for diffusion and viscosity coefficients can provide a way of further improving the chosen form for the full potential energy surface of the system. [ABSTRACT FROM AUTHOR]

He–Li2 interaction potentials, which explicitly include both angular anisotropy and internal vibrational coordinates, have been proposed recently in the literature by extracting them from laser-selected, crossed beam experiments and from the use of various perturbation expansions. In view of the importance of assessing as accurately as possible the dynamical coupling of such internal degrees of freedom during inelastic, low-energy collisions, the present study undertakes a detailed computational comparison of the various possible decoupling schemes which can be employed to treat the above processes. It is found that because of the rather weak nature of the interaction in the title system, nearly all schemes work reasonably well and can be used in scattering calculations. It is, however, shown that the previously suggested potentials need to be modified extensively in order to yield cross sections which agree with the experimental findings. [ABSTRACT FROM AUTHOR]

Rigorous quantum and classical calculations for transport and relaxation properties of the gaseous mixture of He with CO have been carried out over a broad range of temperatures. The interaction potential employed was the one recently suggested from molecular beam experiments (W. Dilling, Ph.D. thesis, University of Göttingen, Germany, 1985) and the calculations were carried out with the correct dynamical couplings between tensorial basis sets in the quantum case, leading to the usual close-coupled (CC) equations. Classical trajectory (CT) calculations were also carried out and compared with the CC results. A combined use of CC and CT results, together with an appropriate choice of partition functions, is found to produce rather good agreement with the experimental findings for diffusion and mixture viscosity coefficients. The present results suggest ways for further testing the original potential energy surface and for extending the multiproperty analysis of it started earlier on with the scattering data of Dilling and the pressure broadening data of Green, Boissoles, and Boulet [J. Quant. Spectrosc. Radiat. Transfer 39, 33 (1988)]. [ABSTRACT FROM AUTHOR]

Full quantum calculations of several transport and relaxation cross sections have been carried out for the title system, using the multiproperty potential energy surface obtained earlier by Gianturco et al. [Chem. Phys. 109, 417 (1986)] which has been recently shown to be one of the most reliable descriptions of the He–N2 interaction. A rigorous close coupling (CC) treatment of the scattering problem turns out to be the only realistic choice for evaluating viscomagnetic relaxation data and for anisotropy-dependent nonequilibrium properties. A comparison of the present calculations with classical trajectory (CT) estimates is carried out for several transport cross sections as function of both the collision energy and the temperature of the mixture. It is clearly shown by the present results that classical treatments markedly differ from the quantum calculations at collision energies which are comparable with the average well depth of the chosen interaction. On the other hand, CT and CC values are nearly coincident at higher collision energies for all the computed properties. Thus, their combined use in evaluating the temperature dependence of diffusion and viscosity coefficients reveals the high quality of the present multiproperty interaction vis a vis the experimental findings examined in this work. [ABSTRACT FROM AUTHOR]

We present an approximate quantal model to study the double continuum problem arising in the complete fragmentation of X···BC(v)···Y van der Waals(vdW) complexes, where BC is a conventional diatomic molecule vibrationally excited and X and Y are rare gas atoms, through vibrational predissociation (VP). Assuming a near equilibrium geometry of the complex and using an adiabatic approximation for describing the oscillation in the angle formed by the BC···X and BC···Y weak bonds, the rates for complete fragmentation are expressed in the frame of Fermi’s ‘‘Golden Rule’’. Double continuum wave functions may be obtained by a perturbative treatment that allows one to take properly into account the symmetry of the problem in the particular and very frequent case X≡Y. [ABSTRACT FROM AUTHOR]

Nanoconfined poly(4-methylstyrene) [P(4-MS)] films exhibit reductions in glass transition temperature (Tg) relative to bulk Tg (Tg,bulk). Ellipsometry reveals that 15-nm-thick P(4-MS) films supported on silicon exhibit Tg - Tg,bulk = - 15 °C. P(4-MS) films also exhibit fragility-confinement effects; fragility decreases ∼60% in going from bulk to a 20-nm-thick film. Previous research found that incorporating 2-6 mol  % 2-ethylhexyl acrylate (EHA) comonomer in styrene-based random copolymers eliminates Tg- and fragility-confinement effects in polystyrene. Here, we demonstrate that incorporating 3 mol  % EHA in a 4-MS-based random copolymer, 97/3 P(4-MS/EHA), eliminates the Tg- and fragility-confinement effects. The invariance of fragility with nanoconfinement of 97/3 P(4-MS/EHA) films, hypothesized to originate from the interdigitation of ethylhexyl groups, indicates that the presence of EHA prevents the free surface from perturbing chain packing and the cooperative mobility associated with Tg. This method of eliminating confinement effects is advantageous as it relies on the simplest of polymerization methods and neat copolymer only slightly altered in composition from homopolymer. We also investigated whether we could eliminate the Tg-confinement effect with low levels of 2-ethylhexyl methacrylate (EHMA) in 4-MS-based or styrene-based copolymers. Although EHMA is structurally nearly identical to EHA, 4-MS-based and styrene-based copolymers incorporating 4 mol  % EHMA exhibit Tg-confinement effects similar to P(4-MS) and polystyrene. These results support the special character of EHA in eliminating confinement effects originating at free surfaces., (© 2024 Author(s). Published under an exclusive license by AIP Publishing.)