- Email: [email protected]
Historical perspective on: Neon interatomic potentials from scattering data and crystalline properties [Volume 19, Issue 3, 1 April 1973, Pages 359–362]
Chemical Physics Letters 589 (2013) 12–13
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Historical perspective on: Neon interatomic potentials from scattering data and crystalline properties [Volume 19, Issue 3, 1 April 1973, Pages 359–362] J.M. Farrar a,⇑, Y.T. Lee a, V.V. Goldman b, M.L. Klein c a b c
James Franck Institute and Department of Chemistry, University of Chicago, Chicago, IL 60637, USA Physik Department El 3, Technische Universität München, 8046 Garching bei München, Germany Division of Chemistry, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
Summary by James M. Farrar, Nobel prize-winner: Professor Yuan T. Lee. In the late 1960s and early 1970s, crossed molecular beam ‘supermachines’, outfitted with supersonic atomic and molecular sources and the universal mass spectrometric detector, began to fulfill their promise as probes of chemical dynamics under single-collision conditions [1]. As the ‘Alkali Age’ of molecular beam studies ended, an entirely new chapter in the study of elementary reaction dynamics and chemical kinetics was unfolding. The atmosphere at the University of Chicago was very exciting as theorists like John Light and Stephen Berry talked about phase shifts, deflection functions, semiclassical scattering theory and path integrals. The emerging area of collision theory and its application to chemical problems were alive with promise. And Yuan Lee was in the early days of his career, developing experimental methods that made this new kind of theory accessible to experiment. The emerging area of collision theory and its application to chemical problems was alive with promise. The principal objective of Lee’s research was the study of reactive collisions, but the very active area of interatomic and intermolecular forces [2,3] probed by transport and bulk properties of gases, presented an additional challenge for beam experiments. Measuring differential cross-sections for the elastic scattering of rare-gas atoms – employing atomic beams with the characteristically narrow speed-distributions afforded by supersonic expansion – yielded interatomic potentials, without the thermal averaging inherent in analyzing bulk properties of gases. The first studies from the group, employing atomic beams at 298 K, were groundbreaking, as observations of quantum oscillations in the angular distributions probed the low-energy repulsive interaction in the helium and neon dimers [4]. The group also observed the effect of nuclear symmetry in Ne–Ne collisions [5] and rainbow scattering in the Ar–Ar system [6]. For the helium and neon rare-gas pairs, a probe of the potential in the vicinity of the very shallow attractive well (11 K in He2, 42 K in Ne2) [7], required collision energies only a few times the well⇑ Corresponding author. Fax: +1 5852760205. E-mail addresses: [email protected] (J.M. Farrar), [email protected] (Y.T. Lee). 0009-2614/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cplett.2013.08.039
depth, and it was my task to design and assemble a beam source that would allow rare-gas atomic beams to be cooled to cryogenic temperatures. Under the tutelage of colleagues Peter Siska, John Parson, and Trudy Schafer, I learned how to use ‘Machine A’ to conduct differential scattering measurements, first with two crossed beam of helium atoms cooled to liquid hydrogen temperature [8], and then on a number of systems including the neon dimer [9], with liquid-nitrogen-cooled beams. Practitioners recognized that potentials optimized not only for the results of scattering cross-sections, but also selected properties of bulk materials, were most likely to be reliable for predictive purposes, and the ‘multiproperty’ potential function became de rigueur in the field. Initially the Lee group included comparisons of second virial coefficients calculated from scattering potentials with experimental data, which resulted in improved error-limits on the potential functions. As the experiments on neon concluded, the group was extraordinarily fortunate in establishing a collaboration with Michael Klein, then at the National Research Council of Canada. Michael was a pioneer in the development of large-scale molecular dynamics (MD) simulations of rare-gas solids. It was gratifying to find that the pair potential producing the most reliable MD simulation of the lattice energy of the solid, the sublimation pressure, and the bulk compressibility was in close agreement with the scattering potential. Although the range of computational and experimental methods brought to bear on the problem of atomic and molecular collisions has expanded significantly in the past 40 years, the nature of intermolecular interactions is still a central question, and multiproperty analysis continues to be the preferred way of determining potential functions in more complex systems [10,11]. Then as now, interactions between experimentalists and theorists made the field of chemical dynamics rich and vibrant. References [1] Y.T. Lee, J.D. McDonald, P.R. LeBreton, D.R. Herschbach, Rev. Sci. Instrum. 40 (1969) 1402. [2] G.C. Maitland, M. Rigby, E.B. Smith, W.A. Wakeham, Intermolecular Forces: Their Origin and Determination, Clarendon Press, Oxford, 1981. [3] J.O. Hirschfelder, C.F. Curtiss, R.B. Bird, Molecular Theory of Gases and Liquids, Wiley, New York, 1964. [4] P.E. Siska, J.M. Parson, T.P. Schafer, Y.T. Lee, J. Chem. Phys. 55 (1971) 5762.
J.M. Farrar et al. / Chemical Physics Letters 589 (2013) 12–13 [5] P.E. Siska, J.M. Parson, T.P. Schafer, F.P. Tully, Y.C. Wong, Y.T. Lee, Phys. Rev. Lett. 25 (1970) 271. [6] J.M. Parson, P.E. Siska, Y.T. Lee, J. Chem. Phys. 56 (1972) 1511. [7] J.M. Farrar, T.P. Schafer, Y.T. Lee, Transport phenomena, in: Second International Centennial Boltzmann Seminar, AIP Publishing, Providence, RI, 1973, p. 279.
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[8] J.M. Farrar, Y.T. Lee, J. Chem. Phys. 56 (1972) 5801. [9] J.M. Farrar, Y.T. Lee, V.V. Goldman, M.L. Klein, Chem. Phys. Lett. 19 (1973) 359. [10] D. Cappelletti, F. Vecchiocattivi, F. Pirani, E.L. Heck, A.S. Dickinson, Mol. Phys. 93 (1998) 485. [11] D. Cappelletti, M. Bartolomei, E. Carmona-Novillo, F. Pirani, G. Blanquet, F. Thibault, J. Chem. Phys. 126 (2007) 064311.
Contents lists available at ScienceDirect
Chemical Physics Letters journal homepage: www.elsevier.com/locate/cplett
Historical perspective on: Neon interatomic potentials from scattering data and crystalline properties [Volume 19, Issue 3, 1 April 1973, Pages 359–362] J.M. Farrar a,⇑, Y.T. Lee a, V.V. Goldman b, M.L. Klein c a b c
James Franck Institute and Department of Chemistry, University of Chicago, Chicago, IL 60637, USA Physik Department El 3, Technische Universität München, 8046 Garching bei München, Germany Division of Chemistry, National Research Council of Canada, Ottawa, Ontario K1A 0R6, Canada
Summary by James M. Farrar, Nobel prize-winner: Professor Yuan T. Lee. In the late 1960s and early 1970s, crossed molecular beam ‘supermachines’, outfitted with supersonic atomic and molecular sources and the universal mass spectrometric detector, began to fulfill their promise as probes of chemical dynamics under single-collision conditions [1]. As the ‘Alkali Age’ of molecular beam studies ended, an entirely new chapter in the study of elementary reaction dynamics and chemical kinetics was unfolding. The atmosphere at the University of Chicago was very exciting as theorists like John Light and Stephen Berry talked about phase shifts, deflection functions, semiclassical scattering theory and path integrals. The emerging area of collision theory and its application to chemical problems were alive with promise. And Yuan Lee was in the early days of his career, developing experimental methods that made this new kind of theory accessible to experiment. The emerging area of collision theory and its application to chemical problems was alive with promise. The principal objective of Lee’s research was the study of reactive collisions, but the very active area of interatomic and intermolecular forces [2,3] probed by transport and bulk properties of gases, presented an additional challenge for beam experiments. Measuring differential cross-sections for the elastic scattering of rare-gas atoms – employing atomic beams with the characteristically narrow speed-distributions afforded by supersonic expansion – yielded interatomic potentials, without the thermal averaging inherent in analyzing bulk properties of gases. The first studies from the group, employing atomic beams at 298 K, were groundbreaking, as observations of quantum oscillations in the angular distributions probed the low-energy repulsive interaction in the helium and neon dimers [4]. The group also observed the effect of nuclear symmetry in Ne–Ne collisions [5] and rainbow scattering in the Ar–Ar system [6]. For the helium and neon rare-gas pairs, a probe of the potential in the vicinity of the very shallow attractive well (11 K in He2, 42 K in Ne2) [7], required collision energies only a few times the well⇑ Corresponding author. Fax: +1 5852760205. E-mail addresses: [email protected] (J.M. Farrar), [email protected] (Y.T. Lee). 0009-2614/$ - see front matter Ó 2013 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.cplett.2013.08.039
depth, and it was my task to design and assemble a beam source that would allow rare-gas atomic beams to be cooled to cryogenic temperatures. Under the tutelage of colleagues Peter Siska, John Parson, and Trudy Schafer, I learned how to use ‘Machine A’ to conduct differential scattering measurements, first with two crossed beam of helium atoms cooled to liquid hydrogen temperature [8], and then on a number of systems including the neon dimer [9], with liquid-nitrogen-cooled beams. Practitioners recognized that potentials optimized not only for the results of scattering cross-sections, but also selected properties of bulk materials, were most likely to be reliable for predictive purposes, and the ‘multiproperty’ potential function became de rigueur in the field. Initially the Lee group included comparisons of second virial coefficients calculated from scattering potentials with experimental data, which resulted in improved error-limits on the potential functions. As the experiments on neon concluded, the group was extraordinarily fortunate in establishing a collaboration with Michael Klein, then at the National Research Council of Canada. Michael was a pioneer in the development of large-scale molecular dynamics (MD) simulations of rare-gas solids. It was gratifying to find that the pair potential producing the most reliable MD simulation of the lattice energy of the solid, the sublimation pressure, and the bulk compressibility was in close agreement with the scattering potential. Although the range of computational and experimental methods brought to bear on the problem of atomic and molecular collisions has expanded significantly in the past 40 years, the nature of intermolecular interactions is still a central question, and multiproperty analysis continues to be the preferred way of determining potential functions in more complex systems [10,11]. Then as now, interactions between experimentalists and theorists made the field of chemical dynamics rich and vibrant. References [1] Y.T. Lee, J.D. McDonald, P.R. LeBreton, D.R. Herschbach, Rev. Sci. Instrum. 40 (1969) 1402. [2] G.C. Maitland, M. Rigby, E.B. Smith, W.A. Wakeham, Intermolecular Forces: Their Origin and Determination, Clarendon Press, Oxford, 1981. [3] J.O. Hirschfelder, C.F. Curtiss, R.B. Bird, Molecular Theory of Gases and Liquids, Wiley, New York, 1964. [4] P.E. Siska, J.M. Parson, T.P. Schafer, Y.T. Lee, J. Chem. Phys. 55 (1971) 5762.
J.M. Farrar et al. / Chemical Physics Letters 589 (2013) 12–13 [5] P.E. Siska, J.M. Parson, T.P. Schafer, F.P. Tully, Y.C. Wong, Y.T. Lee, Phys. Rev. Lett. 25 (1970) 271. [6] J.M. Parson, P.E. Siska, Y.T. Lee, J. Chem. Phys. 56 (1972) 1511. [7] J.M. Farrar, T.P. Schafer, Y.T. Lee, Transport phenomena, in: Second International Centennial Boltzmann Seminar, AIP Publishing, Providence, RI, 1973, p. 279.
13
[8] J.M. Farrar, Y.T. Lee, J. Chem. Phys. 56 (1972) 5801. [9] J.M. Farrar, Y.T. Lee, V.V. Goldman, M.L. Klein, Chem. Phys. Lett. 19 (1973) 359. [10] D. Cappelletti, F. Vecchiocattivi, F. Pirani, E.L. Heck, A.S. Dickinson, Mol. Phys. 93 (1998) 485. [11] D. Cappelletti, M. Bartolomei, E. Carmona-Novillo, F. Pirani, G. Blanquet, F. Thibault, J. Chem. Phys. 126 (2007) 064311.