High-resolution thermal-conductivity and heat-capacity studies were carried out on the same sample in the vicinity of the smectic-A–to–smectic-C transition of N-(4-n-heptyloxybenzylidene)-4’-n-butylaniline (70.4). The heat capacity shows a mean-field jump and can be well described by an extended-mean-field model. The thermal conductivity also shows a jump near the smectic-A–smectic-C transition. Instead of a smooth thermal diffusivity, as predicted by a conventional dynamic theory, we found both a peak and a dip in the thermal diffusivity near the transition temperature.

An algebraic error in an earlier paper [J. Zyss and J. L. Oudar, Phys. Rev. A 26, 2028 (1982)] led to an interpretation regarding the desirable polarizability characteristics of a molecule for second-harmonic generation in crystals which is opposite to that actually desired. Optimum response is obtained from crystals comprised of molecules with significant in-plane polarizabilities.

A scaling law is derived relating the static and the dynamic scaling exponents for the width of an interface growing through ballistic deposition, and is applied to recent numerical results of Meakin et al. [Phys. Rev. A 34, 5091 (1986)].

We present the result of a theoretical study of the $3pnp{}_{}{}^1{}_{}{}^{}S$ autoionization states above the first ionization threshold of the magnesium atom. By transferring the dominating configuration interaction between $3p^2$ and $3s^2$ configurations into the bound component of the state function of the autoionization state, the remaining interaction strength between the bound component and the background open channel can be represented by a second-order perturbation contribution in a simple application of the Fano procedure. The calculated width of the $3p^2{}_{}{}^1{}_{}{}^{}S$ state is found to be in excellent agreement with recent two-step two-color photoionization experiment.

We interpret recent experimental data on double ionization of helium by impact of ions with charges between 15 and 44. An independent-electron model is used. It is shown that quantitative agreement can be obtained when the "saturation" effect in the single-electron ionization probability is accounted for at small impact parameters.

We report the implementation of a first-order nondegenerate adiabatic theory for vibrational excitation of ${\mathrm{H}}_2$ by electrons with energies from threshold to 10 eV. Solution of the scattering equations in this method is far simpler than in a full close-coupling calculation because the method is based on an adiabatic factorization of the electron-molecule scattering ket. The method, however, yields low-energy cross sections that are far more accurate than those of traditional adiabatic-nuclei approximations because its transition matrix is calculated off the energy-momentum shell.

We formulate a nonperturbative approximation for treating the multiphoton ionization of an atom. Our approximate ionization amplitude is the time average of the matrix element for the electron, having absorbed enough photons to reach the continuum threshold, to jump into the continuum state represented by the Kroll-Watson scattering wave function.

Two-photon processes induced by a stochastic field, frequency-modulated by a Gaussian noise, are experimentally investigated in a $S=\frac{1}{2}$ spin system at microwave frequency. The shape and the width of the power spectra of the second-order two-photon-induced response of the spin system are measured for wide ranges of the rms amplitude and of the correlation time of the frequency fluctuations of the driving field.

We demonstrate that squeezed states of the radiation field in a free-electron laser are possible only in the small gain and inverse regimes. Moreover, in these regimes, the feasibility of generating squeezed radiation is severely constrained by the quantum fluctuations in the initial states of the electron beam.

A polarization technique based on the detection of Zeeman quantum beats in transmission is applied to the determination of multipole relaxation rates in ground or near-ground atomic levels. With an appropriate choice of polarization and geometry, beat signals are obtained whose decay directly yields the relaxation rates of orientation or alignment. The technique has been used to study collisional depolarization in the $4f^{6}6s^2{}_{}{}^7{}_{}{}^{}F_1^{}{}_{}{}^{}$ near-ground level of Sm I by rare-gas perturbers. Derived cross sections are compared with previous, widely differing determinations.

We present variational calculations of the energy levels of the $\mathrm{td}\mu$ ion relevant for muon-catalyzed fusion. We used very large generalized Hylleraas basis sets. For all the levels the results are better than literature data. For the most important, weakly bound state of $\mathrm{td}\mu$ we obtained a binding energy of 660.01 meV which we estimate to be accurate to about 0.1 meV. For the remaining states the energies converge much faster and we were able to achieve accuracy of about 1 μeV or better.

Reaction-limited cluster-cluster aggregation is investigated using three different models. Simulations of these models suggest that (i) the fractal dimension for mobility-dependent processes is sensitive to the details of the model, (ii) the reaction kernel $K\left(\mathrm{ii}\right)\mathrm{}\sim i^{1.1}$, unless there exists a slow crossover to $i^{1.0}$, (iii) the effective cluster-size-distribution exponent $\tau$ has a value closer to 2.0 than 1.5, and (iv) if the probability that two clusters will join depends on their mobility, then a value of $\tau$ less than 1.5 might be expected.

Dissipative systems represented by two-dimensional maps exhibit a sequence of critical Jacobians where strange attractors are extinguished. Not only the scaling, but even the numerical values of these critical Jacobians are universal. Different physical systems are analyzed that exhibit this behavior, and the rapid convergence to this universal sequence is explained.

Laser-induced molecular reorientation and the associated Freedericksz transition in nematic films of 4′-$n$-pentyl-4 cyanobiphenyl (5CB) with an air interface are studied. The results indicate that the 5CB-air interface actually behaves like a hard boundary in orienting the liquid-crystal molecules, but it allows an enhanced "backflow" in the medium through the orientation-flow coupling, which significantly speeds up the relaxation of molecular orientation. Theoretical analysis using the continuum theory is shown to be in good agreement with the experimental observations.

The quantum states of an electron in a hierarchical potential are investigated in the tightbinding approximation. The hierarchy is taken to be in the transition matrix elements, in natural analogy to the classical problem of diffusion in ultrametric structures. The energy spectrum is found to be a Cantor set, and analytical results are presented for its scaling properties. The envelope of the wave function is found to decay algebraically for certain energies and to be constant for others. The results are in excellent agreement with high-precision numerical work.

We use the generalized WKB method with the Coulomb wave function as the comparison function to derive expressions for normalizations and phase shifts in a screened Coulomb potential as simple quadrature integrals. We compare our results with exact numerical results and with those of the standard WKB method. In most cases our results are good and more accurate than the standard WKB results. We also obtain the high-energy limits of our expressions and show that they coincide with the first-order high-energy-limit expansion of the analytic perturbation theory.

Molecular orbitals are treated within a functional-integral formalism, and the path integral is built by using Klauder’s continuous-representation theory [J. Math. Phys. 4, 1055 (1963); 4, 1058 (1963)] which generates an overcomplete set of state vectors. The molecular N-electron propagator is introduced by performing the linear-combination-of-atomic-orbitals expansion of molecular orbitals. It is shown that the molecular-orbital theory is the simplest example of the collective-coordinates method. Rearranging the terms of the effective collective Hamiltonian, a mechanical model of the chemical bond is achieved. Lastly, with the saddle-point approximation of the path integral, the well-established Roothaan’s equations are obtained.

We present an idealized model for a sequence of position measurements, and we then take an appropriate limit in which the measurements become continuous. The measurements lead to fluctuations without systematic dissipation, and they rapidly destroy off-diagonal terms in the position basis; thus the pointer basis is position. A modification of the model incorporates systematic dissipation via a feedback mechanism; in the modified model there is no decay of off-diagonal coherence in the position basis.

The rotational transitions R(0) to R(3) in pure HD gas have been studied in absorption with 0.06-${\mathrm{cm}}^{\mathrm{-}1}$ resolution at densities from 2 to 68 amagat at 295 K. The permanent dipole moment of HD was found to be 8.83(28), 7.94(2), 7.88(3), and 8.43(10) for R(0) to R(3), respectively, in units of ${10}^{\mathrm{-}4}$ D. These are in general agreement with ab initio calculations except for an unpredicted strong rotational state dependence. Collisional interference was observed and the interference parameter, proportional to the ratio of the average induced dipole moment to the allowed moment, is negative for R(0) and R(1), positive for R(2) and R(3), and of a magnitude consistent with calculation. Comparisons are made with earlier work, particularly that of McKellar [Can. J. Phys. 64, 227 (1986)].