New data and calculations on collision-induced light scattering in rare gases are presented. The theory and experiment are in quantitative agreement. The spectra are found to be approximately piecewise exponentials whose decay constants are directly related to atomic collision parameters.

We present a direct observation of an ultrafast time-resolved emission spectrum of a dye molecule in solution, the time resolution of the system being 2 × ${10}^{-12\mathrm{}}$ sec. Vibrational relaxation within the vibrational manifold of the excited electronic state of rhodamine 6G occurs within 6 × ${10}^{-12\mathrm{}}$ sec. We discuss the implications of these results for the understanding of homogeneous broadening of excited electronic states of large molecules.

X-ray emission studies in Ar and KCl due to formation of an $L_{23}$ vacancy reveal a low-energy satellite below the main emission peak. Comparison with other data on related processes indicates that this satellite is due to two-electron effects (configuration interaction) in the final state of the emission process.

The electronic density of states of a one-dimensional $\mathrm{AB}$ model alloy with long-range order is calculated in the coherent potential approximation. Impurity states are found inside the energy gap and the energy gap disappears long before the alloy becomes completely disordered. The temperature-dependent long-range order exhibits a first-order order-disorder phase transition which causes a discontinuity in the electronic density of states at the middle of the energy gap at the critical temperature $T_c$.

Prior small-polaron hopping theories have tacitly assumed that the lattice relaxes rapidly enough after a jump to permit the treating of successive hops as independent. We conclude that the appropriate relaxation time is too long to permit consistent application of these theories to intermediate-mobility materials such as NiO and CoO. Furthermore, the activation energies associated with correlated hopping motion may be sufficiently small so that the mobility will not manifest an activated behavior.

Temperature- and frequency-dependent relaxation rates in bismuth have been measured by studies of the magnetic-field-dependent reflectivity of microwave and far-infrared radiation in single-crystal samples. Retardation effects have been taken into account in the analysis of the cyclotron resonance line shapes. The temperature and frequency dependence of the relaxation rates are analyzed in terms of the theory of electron-electron scattering and the experiment provides strong support for electron-electron dominated scattering in bismuth. The experimental results are inconsistent with an electron-phonon dominated scattering mechanism.

A distinctive and strong microwave magnetic transmission resonance mode is reported in ferromagnetic Gd, Fe, and Ni when the static magnetic field is parallel both to the sample foil surface and to the microwave magnetic field. Some evidence exists to show that this may involve sensitive detection of two-magnon processes as in parallel pumping.

We show that, in the presence of a spiral spin structure, a new type of spin-flip mechanism appears, yielding the $\ln T$ dependence similar to the Kondo divergence and making the effective exchange parameter between magnetic atoms temperature dependent in agreement with the observed magnon dispersion curve.

A direct-capture model is used to calculate the cross section for the capture of ${}_{}{}^3{}_{}{}^{}\mathrm{He}$ by tritons. Comparisons with data to 20 MeV show that the energy dependence of the ground-state capture cross section is well accounted for and that there exists substantial $t+{}_{}{}^3{}_{}{}^{}\mathrm{He}$ clustering in the first three ${}_{}{}^6{}_{}{}^{}\mathrm{Li}$ states.

Distorted-wave Born-approximation calculations have been done for the reactions ${}_{}{}^{40,48}{}_{}{}^{}\mathrm{Ca}\mathrm{}(t,p)\mathrm{}{}_{}{}^{42,50}{}_{}{}^{}\mathrm{Ca}_{\mathrm{g}.\mathrm{s}.\mathrm{}}^{}{}_{}{}^{}$. A finite-range interaction was used, which acted between the proton and each transferred neutron. The results support conclusions of zero-range ($t,p$) calculations, both with respect to the shapes of the angular distributions, and the relative cross sections for stripping into different shells. However, the calculated absolute cross section is about one third of that observed.

We determine the dynamics of a spherically symmetric, thin-shelled ensemble of collisionless particles. All the stable and unstable equilibrium configurations (which we find to be stable against single-particle decay) are classified with the help of a variational principle. Applying this principle to zero—rest-mass particles (e.g., gravitational geon), we find that quantum geometrodynamics must be applied when the geon has low angular momentum and is in its ground state.

Measurements of the ratio of the deuteron to proton electric form factors, $\frac{G_E\mathrm{}\left(d\right)\mathrm{}}{G_E\mathrm{}\left(p\right)\mathrm{}}$, were made from elastic electron-deuteron scattering to a precision of approximately 1% for the range of momentum transfers $0.10<~q^2<~0.8$ ${\mathrm{F}}^{-2\mathrm{}}$. Within experimental errors the slope as obtained from the ratio $\frac{G_E\mathrm{}\left(n\right)\mathrm{}}{G_E\mathrm{}\left(p\right)\mathrm{}}$ agrees with the extrapolated thermal neutron-electron interaction slope when relativistic corrections and Feshbach-Lomon deuteron wave functions are applied. The deuteron radius was found to be 1.95 ± 0.02 F, the same as predicted by the Feshbach-Lomon calculation.

We have determined the hyperfine interval $\Delta \nu$ and the muon moment ${\mu }_{\mu }=\frac{g_{\mu }^{}{}_{}{}^{\prime }{\mu }_{\mathrm{B}}}{2}$ from the frequencies of the two alternative Zeeman transitions in muonium, working at that "magic" field where $\frac{\partial {\nu }_1}{\partial B}=\frac{\partial {\nu }_2}{\partial B}=0\mathrm{}$. Extrapolating determinations of $\Delta \nu$ in Kr and Ar to zero pressure, we obtain consistent results, yielding jointly $\Delta \nu \mathrm{}\left(0\right)=4463.3022\mathrm{}\left(89\right)\mathrm{}$ MHz. Assuming that $g_j\mathrm{}\left(M\right)\mathrm{}$ is unshifted by collisions, we obtain $\frac{g_e}{g_{\mu }^{}{}_{}{}^{\prime }}=206.765\mathrm{}09\left(80\right)\mathrm{}$, which corresponds to $\frac{f_{\mu }}{f_p}=3.183\mathrm{}373\left(13\right)\mathrm{}$. The combination of these results gives ${\alpha }^{-1\mathrm{}}-137=0.036\mathrm{}54\left(30\right)\mathrm{}$ (2.1 ppm in ${\alpha }^{-2\mathrm{}}$), in good agreement with the recommended value of 0.036 02(21).

Regge-pole and strong-absorption (diffractive) models are based upon fundamentally different physical postulates. Although both reproduce available $\frac{d\sigma }{\mathrm{dt}}$ and polarization data, profound differences are evident in basic amplitude structure. We show that measurements of the spin-rotation parameters $R$ and $A$, for any high-energy exchange process, will determine structure of amplitudes and thus provide unambiguous tests of essential assumptions in the models. We examine explicitly the experimentally feasible reactions $\pi N\to K(\Lambda ,\Sigma )$, $\overline{K}N\to \pi (\Lambda ,\Sigma )$, and $\gamma p\to K(\Lambda ,\Sigma )$, as well as multiparticle processes.

The magnetic-quadrupole transition $\mathrm{}\left(1s2p\right)\mathrm{}{2}^3{P}_2\to \left(1\mathrm{}{s}^2\right)1^1{S}_0$ of the heliumlike atom Ar XVII has been observed. A measurement of the lifetime of this state has been made by the beam-foil time-of-flight technique, with the result $\tau \left(2^3{P}_2\right)=(1.7\mathrm{}\pm 0.3)\times {10}^{-9\mathrm{}}$ sec.

The lifetime of the $2^2{S}_{\frac{1}{2}}$ state of the hydrogenlike atom Ar XVIII has been measured by direct observation of spontaneous two-photon decay in a beam-foil time-of-flight experiment. Identification of the two-photon mode was made using photon counting techniques to observe the single-photon continuum, and the peak resulting from summing the energies of photon pairs detected in coincidence. The measured lifetime, $\tau \left(2^2{s}_{\frac{1}{2}}\right)=3.54\mathrm{}\left(25\right)\mathrm{}\times {10}^{-9\mathrm{}}$ sec (95% confidence) is in excellent agreement with theoretical predictions based on a nonrelativistic calculation.

The linked-cluster many-body perturbation approach has been applied to the study of indirect nuclear spin-spin coupling constant $J_{\mathrm{HD}}$ in HD molecule. The complete set of states used were the bound and continuum states of $\mathrm{H}_2^{}{}_{}{}^{+}$ molecular ion with the internuclear separation appropriate to ${\mathrm{H}}_2$ molecule. Our calculated value of $J_{\mathrm{HD}}$ through the Fermi contact interaction mechanism is +42.57 Hz in good agreement with the most recent experimental value of +42.7±0.7 Hz.

A one-dimensional, two-species numerical-simulation code has been used to study the formation and structure of collisionless electrostatic shocks formed by two colliding plasmas and by a plasma striking a perfectly reflecting piston. Collisionless shocks are formed in hydrogen up to a maximum piston velocity of $M\equiv \frac{v_D}{c_S}\sim 3.5$. Shocks with velocities up to $M\sim 4$ have been produced which have a predominantly laminar structure accompanied by strong collisionless dissipation.

A general scheme of detecting magnetically trapped particles in fusion devices through the observation of echo phenomena is proposed. The conditions for temporal echoes due to the trapped particles are derived and a physical explanation of trapped particle echoes is given.

We analyze the effects of the radial drift of the trapped particles on the drift-wave instability in toroidal systems. These effects appear as $O\left(\sqrt{\epsilon }\right)$ corrections to the dispersion relation, $\epsilon$ being the toroidicity. Instabilities due to the drift orbit are found in the following limits: (a) $a_e\gg \frac{\omega }{k_{\parallel }}\gg a_i$, ${\epsilon }^{\frac{1}{2}}{a}_e$, (b) ${\epsilon }^{\frac{1}{2}}{a}_e$, $a_i\gg \frac{\omega }{k_{\parallel }}>{\epsilon }^{\frac{1}{2}}{a}_i$, where $a_e$ and $a_i$ are the thermal speeds of the electrons and ions, respectively.