Acceleration and slowing down of nonlinear wave packets in a weakly nonuniform plasma

The processes of acceleration of nonlinear waves in a weakly inhomogenous plasma and slowing down due to nonlinear Landau damping are compared. For initially standing waves the time needed for reaching equilibrium between these oppossing tendencies is estimated.     

A new estimate on the indirect Coulomb energy

Here we prove a new lower bound on the indirect Coulomb energy in quantum mechanics, in terms of the single particle density of the system. The new universal lower bound is an alternative to the classical Lieb–Oxford bound (with a smaller constant, C = 1.45 < C_LO = 1.68) but involving an additive kinetic energy term of the single particle density as well. © 2011 Wiley Periodicals, Inc. Int J Quantum Chem, 2012     

Evidence for proton pairs in γ-AIOOH (boehmite) from NMR absorption spectra

Continuous-wave and Fourier transform NMR absorption spectra have been recorded for pure γ-AIOOH at room temperature and 130K. The well-resolved doublet lineshape shows that there are proton pairs (intrapair separation $\text{R ? 1.7}$ Å), the presence of which has not previously been recognized. A structural model based on the occupation of two sites consistent with the space group Cmcm is proposed.     

NMR study of hydrogen molybdenum bronzes: H1.71MoO3 and H0.36MoO3

Proton NMR relaxation times (T₂T₁, and T_1?) and absorption spectra are reported for the compounds H_1.71MoO₃ (red monoclinic) and H_0.36MoO₃ (blue orthorhombic) in the temperature range 77 K < T < 450 K. Rigid lattice dipolar spectra show that both compounds contain proton pairs, as OH₂ groups coordinated to Mo atoms in H_1.71MoO₃ and as pairs of OH groups in H_0.36MoO₃. The room temperature lineshape for H_1.71MoO₃ shows that the average chemical shielding tensor has a total anisotropy of 20.1 ppm. The relaxation measurements confirm that hydrogen diffusion occurs and give E_A = 22 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 10}{}^{\mathrm{?13}}\text{sec}$ for H_1.71MoO₃ and E_A = 11 kJ mole^?1 and $\text{τ}{}^0{}_{\mathrm{<mtext>C</mtext>}}\text{? 3 × 10}{}^{\mathrm{?8}}\text{sec}$ for H_0.36MoO₃.     

Force constants in hydrogen-bonded crystals

Hydrogen bond stretching force constants in crystals of imidazole, urea and cyanuric acid are calculated using both a modified CNDO/2 method and a constrained least squares fitting of interatomic pair potentials to the lattice vibrations. Results show that the modified CNDO/2 method gives closer agreement with the experimentally derived force constants than the normal CNDO/2 parameterization.     

Defect interactions in alkali halides

Pairwise defect interactions between divalent cation impurities, cation vacancies and anion vacancies have been studied in the extrinsic and intrinsic temperature ranges for the KClSr²⁺ system. Pair correlation functions have been derived for the various defect interactions distinguished by their site symmetries and these show the existence of associated divalent cation—cation vacancy and cation—anion vacancy pairs even at high temperatures. Pair formation gives way to dissociation at low impurity concentrations and high temperatures.     

A simple,reliable model of the bending mode of water

A simple, reliable model of the bending mode vibration of the water molecule based on the Morse oscillator is presented. The model yields accurate predictions of the rotation—vibration level structure in the various ν₂ bands as well as the geometric structure of the ground state.     

Rate coefficient for the reaction OH + HO2 = H2O + O2 at 1 atmosphere pressure and 308 K

The rate coefficient for the reaction OH + HO₂ =H₂O + O₂ has been determined from measurements of the steady-state absorption of HO₂ at 210 nm, in low-frequency square-wave modulated photolysis of O₃ + H₂O mixtures. The value obtained was (9.9 ± 2.5) × 10^?11 cm³ molecule^?1 s^?1 at 308 K and 1 atm pressure.     

Pulsed NMR study of NH4+ β-alumina

Proton NMR relaxation times T₂, T₁, and T_1? are reported for NH₄⁺ β-alumina powder in the temperature range 77 K < T < 500 K at 16 MHz. The measurements show that the NH₄⁺ ions both reorient and translate. The translational process can be characterized by the parameters E = 20 kJ mole^?1 and τ⁰_d = 3 × 10^?11 sec. Relaxation at high temperatures is dominated by dipolar coupling to paramagnetic impurities. Reasons for the different activation energies measured using NMR and other techniques for β-alumina compounds are discussed.     

Laser-induced fluorescence in N2 and N+2 by multiple-photon excitation at 266 nm

The fluorescence transitions corresponding to the second positive system of N₂ (C³Π_u → B³Π_g) for Δv = 0, 1 and the first negative system of N⁺₂(B²Σ⁺_u → X²Σ⁺_g) for Δv = 0, 1, 2 have been observed following laser-induced mul excitation of N₂.