David Logan

Abstract:

An electron paramagnetic resonance spectroscopic study of the reaction of ground-state A1 atoms with NH3 in adamantane at 77 K on a rotating cryostat has demonstrated the formation of three mononuclear Al-NH3 complexes, Al(NH3)4 (A), HA1NH2 (B), and Al(NH3)2 (C). These species have the following magnetic parameters: aAl = 786.3 ± 0.22 MHz, = 23 ± 0.08 MHz, and g = 1.9997 ± 0.0001 for A1(NH3)4, aAl = 922.5 ± 0.41 MHz, an = 228.7 ± 2.00 MHz, = 27 ± 2.0 MHz, aH(1) = 27 ± 2.0 MHz, and g = 2.0003 ± 0.0002 for HAINH2, and a||(Al) = 131.5 MHz, a⊥(1) = ca. 20 MHz, and g||= g⊥ = 1.999 for Al(NH3)2. HAIOH (D) is also formed in this system from adventitious H20 and has the parameters aAl= 911.3 ± 1.06 MHz, aH= 286.4 ± 3.7 MHz, and g = 1.9998 ± 0.0004. © 1992, American Chemical Society. All rights reserved.

Abstract:

We consider a model system of three weakly coupled, weakly anharmonic oscillators, containing two near 2:1 Fermi resonances. This system is initially reduced via a resonance approximation to one of two coupled pendula, each pendulum representing one of the interoscillator resonances. This leads to a natural description of the system in terms of analytically predictable resonance zones and their intersection in action space. A full numerical analysis of the classical dynamics of the two-pendulum system is given, with respect to both the appearance of stochasticity and the development of periodic orbits in the resulting two-dimensional area-preserving map. The success of the resonance approximation in describing adequately the behavior of the three-oscillator model is shown by comparison with a representative study of the classical dynamics of the full three-oscillator model. © 1992 American Institute of Physics.

Abstract:

Using a self-consistent mean-field approach to a disordered Hubbard model the authors show that, regardless of the role of correlation in the half-filled band for which the conventional phenomenology is recovered, correlation effects can be strongly enhanced by disorder in the low-filling limit, leading to a well-defined quasi-atomic domain of strong local moments on an inhomogeneous scale. They argue that the theory provides a natural origin for the observed behaviour of the Cs-rich liquid alloys Cu-Au close to stoichiometry.