Laser-light-scattering and electron-spin-resonance spectroscopies have been used to measure the translational and the rotational diffusion coefficients of human albumin. In the framework of the Debye-Stokes-Einstein theory, the two coefficients yielded two significantly different values for the hydrodynamics radius of the biomolecule. The discrepancy is discussed in connection with the involvement of the solvent internal degrees of freedom.

Measurements are reported for line-intensity ratios emitted from heliumlike B iv ions in a plasma with $N_e$=1.5×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$ and ${\mathrm{kT}}_e$=175 eV. The plasma was produced in a theta-pinch discharge. The analysis supports theoretical excitation rates calculated in the distorted-wave approximation, which include the effect of resonances.

The far-infrared spectrum of dilute solutions of HCl and DCl in liquid ${\mathrm{SF}}_6$ have been calculated by applying of two non-Markovian spectral theories previously reported in a recent work [A. Calvo Hernández, S. Velasco, and F. Mauricio, Phys. Rev. A 31, 3419 (1985)]. The calculated spectra are compared with the experimental spectra. Even though the systems under study are relatively far from the Markovian limit, the agreement between theoretical and experimental spectra shows the wide range of validity of both non-Markovian spectral theories.

After transforming a charged-particle action from Lagrangian to Eulerian notation according to standard techniques we obtain Euler-Lagrange equations which are equivalent to the Maxwell-Lorentz force set. These equations differ from those reported previously in the literature and lead to the conclusion that a quantity often referred to as ‘‘the canonical momentum of a charged fluid’’ is not necessarily a constant of the fluid’s motion.

Depending on the distribution of energy between the scattered positron and the ejected electron in the final channel, two competing processes are involved in positron-impact ionization of atoms, namely (a) direct head-on ionization of an electron and (b) positronium formation to the continuum. Using Faddeev’s three-body scattering formalism for positron–hydrogen-atom collisions, we get an amplitude which takes account of both these processes. The doubly differential cross section thus obtained for the forward scattering angle shows a cusp when plotted against the emission energy. The cusp is due to the effect of positronium formation to the continuum and heretofore has not been predicted.

About 15 years ago Williams, Faller, and Hill (WFH) carried out a modern version of the classic null experiment which tests Coulomb’s law. Their high-precision measurements of the voltage furnish the most stringent upper limit for the parameter δ, which measures a (possible) deviation from the inverse-square form of Coulomb’s law. We show that the experiment of WFH is actually about three times more sensitive to the parameter δ than they supposed by carrying out a careful analysis of the geometrical factor involved in the interpretation of their experiment. The new upper limit for δ is (1.0±1.2)×${10}^{\mathrm{-}16}$

Electron capture and loss cross sections have been measured for highly charged (q=13+) sulfur ions with energies 2.5–200 MeV colliding with helium. Electron capture varies by nearly six orders of magnitude over the energy range investigated, while electron loss varies by only about a factor of 2. The capture cross sections are in reasonable agreement with classical and empirical scaling rules, while the loss cross sections agree well with the plane-wave Born approximation.

We have studied the effect of reactant Na(3p) polarization on the rotational angular momentum alignment of product ${\mathrm{Na}}_2$${\mathrm{}}^{+}$ ions arising from associative-ionization (AI) collisions. Our results show that sensitivity of the AI rate constant to initial atomic polarization persists even when all hyperfine states are populated with broadband (3 ${\mathrm{cm}}^{\mathrm{-}1}$) pulsed laser excitation of Na${(\mathrm{}}^2$$P_{3/2}$) and that the spatial distribution of product rotational angular momentum vectors is anisotropic. We discuss a qualitative description of the collision process consistent with our measurements which indicates that σ-orbital symmetry is preferred to π-orbital symmetry as the colliding partners approach.

The evaporation of monomers following electron-impact ionization causes a significant enhancement of the intensity anomalies (‘‘magic numbers’’) in mass spectra of xenon clusters. The dissociation rates are measured on a microsecond time scale for clusters containing between 10 and 79 atoms. The highest dissociation probability, 99(1)%, is found for ${\mathrm{Xe}}_{57}$${\mathrm{}}^{+}$, which is two atoms larger than a closed-shell icosahedral cluster. Each anomaly in the dissociation rates corresponds to an intensity anomaly (‘‘magic number’’) in the mass spectrum. Recent Monte Carlo simulations for ${\mathrm{Xe}}_{\mathrm{n}}$${\mathrm{}}^{+}$, n≤30, are in full agreement with our experimental results.

Quantum beats due to the hyperfine interaction were observed in the 6$D_{3/2}$→5$P_{1/2}$ transition in ${}_{}{}^{85}{}_{}{}^{}\mathrm{Rb}$. Good agreement with theory was obtained, allowing determination of the values for the magnetic dipole (a=2.32±0.06 MHz) and electric quadrupole (b=1.62±0.06 MHz) hyperfine constants for the upper state.

Absorption spectra of the high-n molecular Rydberg states of ${\mathrm{CH}}_3$I, perturbed by varying number densities of argon (up to ∼11×${10}^{20}$ ${\mathrm{cm}}^{\mathrm{-}3}$), are reported. Red shifts, which increase with increasing argon number density, are observed for both discrete and autoionizing states. These red shifts vary linearly with the perturber number density for principal quantum numbers n≥10. We explain these results quantitatively on the basis of the electron scattering length in argon, as well as the polarization of the medium by ${\mathrm{CH}}_3$${\mathrm{I}}^{+}$.

Precision measurements of the absolute wavelengths of the Lyman-α doublet (2p ${\mathrm{}}^2$$P_{3/2}$,1/2 →1s ${\mathrm{}}^2$$S_{1/2}$) in hydrogenlike argon (${\mathrm{Ar}}^{17+}$), as well as those of some strong dielectronic satellites, are reported. The Alcator C tokamak plasma was seeded with trace amounts of argon and the emission spectra were taken with a high-resolution, crystal x-ray spectrometer. In situ wavelength calibration was achieved by utilizing the potassium Kα lines from a KCl fluorescence source. For the Ly${\alpha }_2$ line, a precision of 11 ppm was achieved. Comparisons of these data with QED predicted wavelengths show good agreement, yielding a test of the 1s Lamb shift at the 3% level. The precision of these measurements was limited by uncertainties in the wavelength calibration, with the uncertainties due to the influence of unresolved satellites being of secondary importance.

We have studied the effect of well-characterized laser frequency fluctuations on the saturation of an atomic resonance in a double optical resonance experiment. The peak-height asymmetry of the observed Autler-Townes signal was reversed at small detunings when the shape of the saturating laser power spectrum was changed from nearly Gaussian to nearly Lorentzian. This behavior agrees qualitatively with theoretical calculations and also with previous observations using lasers without such well-characterized fluctuations.

It is shown theoretically that double resonance through the continuum can be utilized to produce two photon-dressed discrete states embedded in the continuum. The significance of creating such a pair of states is discussed, along with its experimental consequences. Especially important are quantum beats of population, which offer novel spectroscopic opportunities.

We extend to dimensions d≥2 our scaling treatment of the perimeter occupancy probabilities for diffusion-limited aggregation (DLA) clusters grown on lattices. We obtain an analytic relation for the Hausdorff dimension D. We find no upper critical dimension for DLA, although D→d-1 for large d. Our theoretical values for D are fully consistent with Meakin’s Cartesian lattice simulations for 2≤d≤6. We have studied the nonuniversality (lattice dependence) of D by shearing the Cartesian lattices. For maximal shear, D=d-1 (mean field) for d≥3.

The first example of nematic reentrance in a mixture of a side-chain liquid-crystalline polymer with a low-molecular-weight nematogen is described. In addition, we show by x-ray measurements of the layer spacing in the $S_A$ phase, that, in this case too, a problem of competing lengths exists, although both compounds are terminally nonpolar mesogens.

The spectrum of a laser-produced gold plasma (3.0–4.0 Å) was interpreted by Kiyokawa et al. [Phys. Rev. Lett. 54, 1999 (1985)] as due to multiple inner-shell vacancy states of ${\mathrm{Au}}^{26+}$–${\mathrm{Au}}^{32+}$. New extended observations (3.5–6.1 Å) obtained from a similar Au plasma with a better resolution lead to unambiguous identification of several emission lines of ${\mathrm{Au}}^{51+}$, and an alternative theoretical interpretation of all spectral features from 3.0–3.8 Å is proposed in terms of unresolved transition arrays (3d-5f and 3d-6f types) of ${\mathrm{Au}}^{52+}$–${\mathrm{Au}}^{48+}$.

The film drained behind Saffman-Taylor fingers is studied experimentally. The film thickness is found to be in good agreement with theory. It is further shown that previous disagreement between theory and experiment in the Saffman-Taylor problem is partly due to the existence of this film.

Accurate eigenvalues of Schrödinger’s nonrelativistic equation for Be (1$s^2$2s2p${)}^3$P and ${\mathrm{Be}}^{\mathrm{-}}$ (1$s^2$2s2$p^2$${)}^4$P have been calculated yielding a corresponding electron affinity A of 276.1±6.5 meV. The absolute term value of ${\mathrm{Be}}^{\mathrm{-}}$ (relative to the Be ground state) obtained as the difference between the experimental term value of Be ${}_{}{}^3{}_{}{}^{}\mathrm{P}$ and A is 2.4492±0.0065 eV, in agreement with a recent measurement of 2.53±0.11 eV.

For a bare Coulomb potential energy -${\mathrm{Ze}}^2$/r, it is shown that the total electron density ρ(r) for an arbitrary number of closed shells is given by ρ(r)=(2Z/$a_0$) ${\mathcal{F}}_r^{\infty }$${\rho }_s$(r)dr where ${\rho }_s$ is the s-state contribution to ρ(r). This yields Kato’s theorem [∂ρ(r)/∂r${]}_{r=0\mathrm{}}$=(-2Z/$a_0$)ρ (r=0) as a limiting case. That ∂ρ/∂r is always negative follows, for all distances r. For the nth closed shell, with density ${\rho }_n$(r), it is further shown that $R_{n0}$(r)=[(-$a_0$/2Z)∂${\rho }_n$/∂r] ${}_{}{}^{1/2}{}_{}{}^{}$, with $R_{n0}$ the s-state radial wave function. This result can be used to construct an explicit differential equation for ${\rho }_n$(r).