Studies in hydrogen bonding: Association within mixed dimers of water,methanol, ammonia,and methylamine using the empirical potential EPEN

An empirical potential EPEN has been used to find the stable geometries and approximate hydrogenbond energies of the mixed dimers formed between molecules of water, methanol, ammonia, and methylamine. These results are compared with results in the literature obtained using ab initio methods.     

Relativistic theory of surface states

A Green's function method is used to investigate the role of relativistic effects in determining the electronic states in a semi-infinite Kronig-Penney model. Various boundary conditions are considered and it is found that relativistic effects do not introduce new surface states.     

The thermodynamic solvate difference rule: solvation parameters and their use in interpretation of the role of bound solvent in condensed-phase solvates

Our earlier-established thermodynamic solvate difference rule encompasses thermodynamic relationships for the quantities P=DeltafH degrees, DeltafG degrees, DeltafS degrees, S degrees, Vm, and UPOT for pairs of condensed-phase solvates (including hydrates) having n and m moles, respectively, of bound solvent (including water, i.e., L=H2O), and can be written as P{MpXq.nL,p} approximately P{MpXq.mL,p}+(n-m).thetaP{L,p-p} (with m=0 for the corresponding thermodynamic quantity of the condensed-phase unsolvated parent, P{MpXq,p}), where thetaP{L,p-p} is the incremental contribution per mole of the bound solvent, L, to the property, P, of the solvate in condensed phase, p (where p=solid or liquid). We find that this rule can be extended to supercooled NaOH (and, probably, even more generally). Once established, the parameter thetaP{L,p-p} provides approximate values of the thermodynamic property, P, for the remaining solvates (hydrates) for which data are unknown. The difference rule is here further extended to heat-capacity data, Cp, for both hydrates and other solvates. For solid-phase hydrates, thetaCp{H2O,s-s} is determined to be 42.8 J K(-1) mol(-1). Further, the method is shown to apply also to the organic solvates, DMSO and DMF (the latter is based on a single example), leading to the (tentative) values thetaCp{DMSO,s-s} approximately 105 J K(-1) mol(-1) (at 255 K); approximately 161 J K(-1) mol(-1) (at 350 K), illustrating typical temperature dependence of the thetaCp values. thetaCp{DMF,s-s} approximately 84 J K(-1) mol(-1). For supercooled NaOH, thetaCp{NaOH,l-l}=77 J K(-1) mol(-1). The values of the solvate difference rule parameters provide us with insight into the bonding condition of the solvent molecule, leading to the conclusion that bound solvent water in an ionic environment is ice-like. The situation is more complex within zeolites because water may enter the solvate in a variety of ways. These latter considerations are also briefly discussed with respect to fullerenes.     

Lattice potential energy estimation for complex ionic salts from density measurements

This paper is one of a series exploring simple approaches for the estimation of lattice energy of ionic materials, avoiding elaborate computation. The readily accessible, frequently reported, and easily measurable (requiring only small quantities of inorganic material) property of density, rho(m), is related, as a rectilinear function of the form (rho(m)/M(m))(1/3), to the lattice energy U(POT) of ionic materials, where M(m) is the chemical formula mass. Dependence on the cube root is particularly advantageous because this considerably lowers the effects of any experimental errors in the density measurement used. The relationship that is developed arises from the dependence (previously reported in Jenkins, H. D. B.; Roobottom, H. K.; Passmore, J.; Glasser, L. Inorg. Chem. 1999, 38, 3609) of lattice energy on the inverse cube root of the molar volume. These latest equations have the form U(POT)/kJ mol(-1) = gamma(rho(m)/M(m))(1/3) + delta, where for the simpler salts (i.e., U(POT)/kJ mol(-1) < 5000 kJ mol(-1)), gamma and delta are coefficients dependent upon the stoichiometry of the inorganic material, and for materials for which U(POT)/kJ mol(-1) > 5000, gamma/kJ mol(-1) cm = 10(-7) AI(2IN(A))(1/3) and delta/kJ mol(-1) = 0 where A is the general electrostatic conversion factor (A = 121.4 kJ mol(-1)), I is the ionic strength = 1/2 the sum of n(i)z(i)(2), and N(A) is Avogadro's constant.     

Stimulated generation of superluminal light pulses via four-wave mixing

We report on the four-wave mixing of superluminal pulses, in which both the injected and generated pulses involved in the process propagate with negative group velocities. Generated pulses with negative group velocities of up to v(g)=-1/880c are demonstrated, corresponding to the generated pulse's peak exiting the 1.7 cm long medium ≈50 ns earlier than if it had propagated at the speed of light in vacuum, c. We also show that in some cases the seeded pulse may propagate with a group velocity larger than c, and that the generated conjugate pulse peak may exit the medium even earlier than the amplified seed pulse peak. We can control the group velocities of the two pulses by changing the seed detuning and the input seed power.     

Correlated fermionic densities for many harmonically trapped particles interacting with repulsive forces

This study is motivated by the very recent work on correlation energy as approximated by the Thomas-Fermi (TF) semiclassical limit [B.R. Landry, et al., Phys. Rev. Lett. 103 (2009) 066401]. In contrast, and motivated by the Hohenberg-Kohn theorem, our work is focussed primarily on the correlated TF ground-state density. We invoke directly the Holas et al. result that for two-fermion systems with harmonic trapping, the fermion-fermion interaction u simply adds to the trapping potential. We conclude this report with some results on correlation kinetic energy for two-fermion systems.     

Onset and saturation of ion heating by odd-parity rotating magnetic fields in a field-reversed configuration

Heating of figure-8 orbit ions by odd-parity rotating magnetic fields (RMF(O)) applied to an elongated field-reversed configuration (FRC) is investigated. The largest energy gain occurs at resonances (s congruent to omega(R)/omega) of the RMF(O) frequency, omega(R), with the figure-8 orbital frequency, omega, and is proportional to s2 for s-even resonances and to s for s-odd resonances. The threshold for the transition from regular to stochastic orbits explains both the onset and saturation of heating. The FRC magnetic geometry lowers the threshold for heating below that in the tokamak by an order of magnitude.