One-dimensional BeH2 polymers: infrared spectra and theoretical calculations

Laser-ablated beryllium atoms react with H2 upon co-condensation in excess hydrogen and neon to form BeH2 and (BeH2)2, which are identified through isotopic substitution and DFT calculations. Unreacted Be atoms isolated in solid neon or hydrogen are excited to the 1P0 state and react further with H2 to enhance the BeH2 and (BeH2)2 concentrations and produce (BeH2)n polymers. The series of strong infrared-active parallel Be-H-Be bridge-bond stretching modes observed for (BeH2)n polymers suggests one-dimensional structures, and this conclusion is supported by DFT calculations. The computed polymerization energy per BeH2 unit is about 33 kcal/mol.     

Matrix infrared spectra and density functional theory calculations of molybdenum hydrides

Laser-ablated Mo atoms react with H2 upon condensation in excess argon, neon, and hydrogen. The molybdenum hydrides MoH, MoH2, MoH4, and MoH6 are identified by isotopic substitution (H2, D2, HD, H2 + D2) and by comparison with vibrational frequencies calculated by density functional theory. The MoH2 molecule is bent, MoH4 is tetrahedral, and MoH6 appears to have the distorted trigonal prism structure.     

FTIR spectroscopic studies of the matrix photoionization and photolysis products of methylene halides

Matrix photoionization of methylene bromide produced absorptions at 1019, 897, and 788 cm^?1 identified previously as CBr₂⁺, CHBr₂⁺, and CHBr₂. High-resolution FTIR spectra revealed overlapping 1/2/1 triplets for natural bromine isotopes with individual linewidths near 0.2 cm^?1. New absorptions at 3121, 2897, and 1345 cm^?1 are assigned to the (CH₂Br⁺)Br cation complex which yields CHBr₂⁺ on photolysis. A substantially increased yield of the CHCl₂⁺ species made possible observation of the CH stretching mode at 3033 cm^?1 and the symmetric CCl₂ stretching mode at 845 cm^?1 along with the previously observed stronger 1291- and 1044-cm^?1 fundamentals. The high resolution and enhanced signal-to-noise capability of the FTIR are clearly demonstrated in this investigation.     

Scaling law for the elastic response of spherical explosion-containment vessels

The substantial progress made in the development of portable, spherical explosion-containment vessels has led to its adoption for explosives-related transporting and manufacturing. A simple scaling law for engineering-design use has been obtained for the maximum first-cycle elastic-strain response to explosive loading by a centered, spherical charge of a representative high explosive known as Pentolite. Results from a computer program based on the work of Baker have been accurately fitted to a six-product power law that is a function of the density, elastic modulus, diameter, and thickness of the vessel and the weight of detonated explosive. Nonlinear and log-linear fits are compared and found to agree if the role of weighting factors is understood. An impulse approximation is used to indicate that the scaling-law parameters are reasonable.     

Dynamic stability of discrete spherical structural systems in fluid media

Summary The dynamic response of a two degree of freedom spherical structural system immersed in viscous fluid media is studied with the fluid reactions obtained byBasset included in the differential equations of motion. Closed form solutions for the response of such systems are presented and a dynamic stability criterion based on the form of the solutions is developed. The solutions and the stability criterion are applicable to the limiting case when the system is surrounded by a vacuum. The various regions of stability and instability are delineated, and it is shown that the type of instability is significantly influenced by the physical properties of the surrounding fluid medium.

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Übersicht Es wird das Verhalten eines mechanischen Systems von zwei Freiheitsgraden untersucht, das aus zwei miteinander verbundenen, kugelförmigen Massen in einer zähen Flüssigkeit besteht. Dabei werden die Zusatzmassen der mitbewegten Flüssigkeit nachBasset in den Bewegungsgleichungen berücksichtigt. Es werden geschlossene Lösungen für die Bewegungen angegeben und daraus die Stabilitätsbedingungen ermittelt. Lösungen und Stabilitätsbedingungen können auch noch auf den Grenzfall eines im Vakuum befindlichen Systems angewendet werden. Die Parameterbereiche für Stabilität und Instabilität werden beschrieben, und es wird gezeigt, daß die Art der Instabilität wesentlich durch die physikalischen Eigenschaften der umgebenden Flüssigkeit bestimmt wird.

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The research upon which this paper is based was supported by the National Science Foundation Grant Nos. GK-479 and GP-2094 to Northwestern University.     

Equilibrium time correlation functions in the low-density limit

We consider a system of hard spheres in thermal equilibrium. Using Lanford's result about the convergence of the solutions of the BBGKY hierarchy to the solutions of the Boltzmann hierarchy, we show that in the low-density limit (Boltzmann-Grad limit): (i) the total time correlation function is governed by the linearized Boltzmann equation (proved to be valid for short times), (ii) the self time correlation function, equivalently the distribution of a tagged particle in an equilibrium fluid, is governed by the Rayleigh-Boltzmann equation (proved to be valid for all times). In the latter case the fluid (not including the tagged particle) is to zeroth order in thermal equilibrium and to first order its distribution is governed by a combination of the Rayleigh-Boltzmann equation and the linearized Boltzmann equation (proved to be valid for short times).Supported in part by NSF Grant PHY 78-22302.     

The classical mechanics of one-dimensional systems of infinitely many particles

We prove a global existence and uniqueness theorem for solutions of the classical equations of motion for a one-dimensional system of infinitely many particles interacting by finite-range two-body forces which satisfy a Lipschitz condition.     

Phase coherent effects in a collisional turbulent plasma

Stochastic fluctuations in a glow-discharge tube show typical turbulent spectra, mode-mode coupling, and evidence of pronounced three-dimensionality.