The authors have measured the projectile and target $L$ x-ray spectra and cross sections for 41-MeV Ta projectiles bombarding thin targets between Ag and Th and for 17-60-MeV collisions of Ho on Ho, Au on Au, Pb on Pb, and U on Th. These cross sections, as well as those measured elsewhere, are examined in terms of a simple vacancy-sharing model involving the $4f\sigma$ and $3d\sigma$ molecular orbitals (MO). From the $\frac{L{\beta }_1}{L\alpha }$ x-ray intensity ratios it is found that in symmetric collisions the $4f\sigma$ MO correlates to the $2p_{\frac{3}{2}}$ level of the collision partners (correlation rule of Barat and Lichten). As the asymmetry of the collision system increases, there is an increasing tendency for the $4f\sigma$ MO to correlate to the $2s$ level of the lower-$Z$ collision partner (correlation rule of Eichler and collaborators). The physical basis for the shift of the $4f\sigma$ MO correlation is discussed.

Binding energies and wave functions of inner-shell electronic states in superheavy quasimolecules with $(Z_p+Z_t)\alpha >1\mathrm{}$ are calculated. Ionization during a collision of very heavy ions is investigated within a molecular basis generated by the solutions of the two-center Dirac equation. Transitions to vacant bound states as well as direct excitation to the continuum are taken into account. We present theoretical values for the ionization probability as a function of impact parameter, bombarding energy, and combined nuclear charge. Our computed results are compared with recent experimental data. It is suggested that relativistic binding energies of electrons in superheavy quasimolecules can be determined experimentally via the impact-parameter dependence of ionization and the anisotropy of quasimolecular radiation.

The $k$-ordering properties of the spectra of atoms and ions consisting of a single valence electron outside a core of closed shells ($k=n+l$) have been introduced and discussed extensively in four previous papers, together with the constant $l$ sequences within each group of levels having the same value of $k$ ($k$ bands). In the present paper, it is demonstrated that the spectroscopic quantum defects ${\delta }_{\mathrm{nl}}$ play the role of the "order parameter" for the $k$-ordering phase of the excited-state spectra. Thus only penetrating orbitals, i.e., those having a large ${\delta }_{\mathrm{nl}}$ (${\delta }_{\mathrm{nl}}\gtrsim 0.2$), exhibit the phenomenon of $k$ ordering, and in particular, the curves of ${\delta }_{\mathrm{nl}}$ vs $l$ (for fixed $k$) are generally curved downwards, with an abrupt decrease to values of ${\delta }_{\mathrm{nl}}$ close to zero at the limiting angular momentum $l_1$, which has been previously introduced. The curves of ${\delta }_{\mathrm{nl}}$ vs $l$ are basically similar to the curves of magnetic field $\overrightarrow{\mathrm{H}}$ as a function of temperature $T$ in a ferromagnet, with an abrupt decrease to ${\delta }_{\mathrm{nl}}\sim 0$ at $l_1$, which can therefore be regarded as the analog of the Curie temperature $T_C$. The "reduced quantum defects" ${\eta }_{\mathrm{nl}}\equiv {\delta }_{\mathrm{nl}}+l-l_1$ (for $l\le l_1$) have also been introduced. It is shown that the ordering of the ${\eta }_{\mathrm{nl}}$ values for $l\le l_1$ determines the nature of the $l$ patterns of the spéctrum, e.g., $\mathrm{dpsf}$, $\mathrm{dpfs}$, or $\mathrm{pdsf}$.

The boomerang model is used to calculate absolute cross sections near the ${}_{}{}^2{}_{}{}^{}\Pi _g^{}{}_{}{}^{}$ shape resonance in $e$-${\mathrm{N}}_2$ scattering. The calculated cross sections are shown to satisfy detailed balancing. The exchange of electrons is taken into account. A parametrized complex-potential curve for the intermediate ${\mathrm{N}}_2^{-}$ ion is determined from a small part of the experimental data, and then used to calculate other properties. The calculations are in good agreement with the absolute cross sections for vibrational excitation from the ground state, the absolute cross section $v=1\mathrm{}\to 2$, and the absolute total cross section.

A 0.3-m vacuum monochromator has been used to observe Lyman-$\alpha$ emission from polycrystalline Mo, Ta, Pt, and Cu and from single-crystal $n$-type Ge and Si surfaces under 6.5-12.5-keV proton bombardment. The viewing direction was fixed at 60° relative to the proton-beam axis. The absolute photon yields were determined as a function of beam-surface incidence angle ($\theta =0\mathrm{}$ for normal incidence) and surface temperature (300-600 °K). Yields exhibited incident angle dependences of $sec\theta$ or stronger, and temperature coefficients were positive for Mo and Ta, negative for Cu, and nearly zero for Ge. Doppler-shift profiles of the Lyman-$\alpha$ emission were used to determine the backscattered, excited-hydrogen-atom energies. Absolute photon yields between about ${10}^{-4\mathrm{}}$ and ${10}^{-2\mathrm{}}$ photons/proton were obtained. The yields were insensitive to background ${\mathrm{H}}_2$ gas pressure between 5×${10}^{-9\mathrm{}}$ and ${10}^{-7\mathrm{}}$ Torr.

Mobilities of singly and doubly charged ions of neon, argon, krypton, and xenon in helium and of xenon in neon have been determined in a drift-tube mass-spectrometer apparatus at temperatures near 300 K and for $10\le \frac{E}{N}\le 100$ Td. The zero-field reduced mobility of a given doubly charged ion is found to be either equal to or slightly smaller than that of its singly charged counterpart. However, the dependences of the mobilities on $\frac{E}{N}$ are found to be strikingly different for the two cases. No difference in mobility is observed between doubly charged ions in the low-lying, metastable states and in their ground state, in contrast to the case of the ions drifting in their parent gases.

A new theory of atomic motion in a resonant or near-resonant electromagnetic wave, based on Ehrenfest's theorem and the optical Bloch equations, is presented. The theory provides a simple unified treatment of the radiation force, including effects of spontaneous emission and induced-dipole interactions. Analytical results are presented for a plane running wave, a general standing wave, a collimated Gaussian beam, and a combination of standing and running waves.

The absorption line shapes of the $R_1\mathrm{}\left(1\right)-R_1\mathrm{}\left(5\right)\mathrm{}$ lines of HF have been measured as a function of pressure for pure HF and with Ar and Kr as buffer gases by means of a cw tunable $F_B$ (II)-type color-center laser operating in the wavelength range from 2.25 to 2.65 μm. Line-broadening coefficients are determined and Einstein $A$ coefficients are evaluated from the line shapes. Collisional narrowing is observed for the $R_1\mathrm{}\left(4\right)\mathrm{}$ line with Kr as the buffer gas.

A technique of third-harmonic generation based on simultaneous resonances in one- and two-quantum transitions was applied to find a level of symmetry ${}_{}{}^1{}_{}{}^{}O_g^{+}{}_{}{}^{}$ of molecular iodine. The energy of this level is given, in ${\mathrm{cm}}^{-1\mathrm{}}$, by $E_T\mathrm{}(n,J)=(35\mathrm{}972.4\pm 0.5)+(132.9\pm 0.2) (n+\frac{1}{2})-(0.34\mathrm{}\pm 0.02){(n+\frac{1}{2})}^2+\left[\right(0.028\mathrm{}57\pm 0.00015)-(0.00015\pm 0.00002\left)n\right]\left(J\right)\mathrm{}(J+1\mathrm{})\mathrm{}$, where $n$ is an integer differing from the vibrational quantum number $v$ by an undetermined integer and $J$ is the angular momentum. This technique has relatively high efficiency in third-harmonic generation and may provide a basis for a new Doppler-free spectroscopy.

A cw tunable dye laser and atomic-beam techniques were used to determine the splittings and separations of the natural Yb isotopes for the 5556.5-Å, ${}_{}{}^3{}_{}{}^{}P_1^{}{}_{}{}^{}-{}_{}{}^1{}_{}{}^{}S_0^{}{}_{}{}^{}$ transition. The resonant scattering was recorded with an instrumental resolution of 7 MHz full width at half-maximum, giving peak separations accurate to ±0.5 MHz. The hyperfine splittings were analyzed to yield values of -0.382(19)% for the hyperfine anomaly and 10.9 GHz/${\mathrm{fm}}^2$ for the field-shift constant; these agree with published values. The optical isotope shifts obtained, along with published electronic and muonic x-ray shifts, were analyzed to yield $\delta 〈r^2〉$ values and a specific mass shift in the range 200-300 MHz. This latter is considerably greater than is normally used for $6s^2-6s6p$ transitions. The model dependence of the isotopic-shift analysis was examined, and the hyperfine anomaly was compared with calculations based on Nilsson wave functions.

We report the first observation of the recoil shift of an optical resonance in the visible part of the spectrum. The method rests on the fact that the recoil shifts have opposite signs for Doppler-generated level crossings with a common upper level and for those having a common lower level. The experiment has been performed with the argon laser at 5145 Å as the source and iodine as the absorber. The measured values are within 12% of the theoretical recoil shift. We give a detailed discussion of the possible influence of shifts of various origins and especially light shifts on the measured frequency differences. We display saturated absorption and saturated dispersion spectra and give formulas for the intensities of the various resonances derived from the corresponding density-matrix diagrams.

A delayed-coincidence technique has been used to measure the lifetime of the $5d6p{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ state of atomic barium. An intermediate, $6s5d{}_{}{}^1{}_{}{}^{}D_2^{}{}_{}{}^{}$ metastable state of barium atoms in an atomic beam was populated by electron bombardment, and a pulsed cw laser was employed to excite atoms from the metastable state to the $5d6p{}_{}{}^1{}_{}{}^{}F_3^{}{}_{}{}^{}$ state. A time-to-amplitude convertor was used to measure the time distribution of the fluorescent light. The value obtained for the lifetime was (44.5±1.8) nsec.

Some recent numerical results for complex resonance eigenvalues of the helium isoelectronic sequence are analyzed in terms of $\frac{1}{Z}$ perturbation theory in order to study the physical factors governing resonance lifetimes. It is pointed out that principal trends in the asymptotic behavior of resonance positions and widths can be rationalized in terms of Hund's rules and familiar principles of bound-state electron-correlation theory, particularly in terms of the radial correlations and their third-order coupling to angular correlations. Such analysis shows, for example, why resonance lifetimes may often shorten with increasing $Z$, even though the $Z=\infty$ (hydrogenic) limit seems to imply an infinite lifetime. The analysis also suggests the possibility of highly correlated, two-electron "bound states" embedded in the continuum for certain critical noninteger values of nuclear charge $Z$.

A time-independent formulation of the problem of scattering in an intense radiation field is used as the basis for a derivation of a low-frequency approximation in which field-free scattering amplitudes enter into the determination of transition amplitudes in the presence of the field. A single-mode field of arbitrary polarization is assumed and the scatterer is represented by a local, short-range potential. In the present derivation the dipole approximation for the field is not assumed. As a result, recoil corrections to earlier versions of the low-frequency approximation are obtained in explicit form. The low-frequency approximation for bremsstrahlung in the absence of a background field, derived some time ago by Low and others, appears as a limiting case of the result obtained here.

The authors have postulated a simple physical model for atomic negative ions and have obtained general formulas to describe their photodetachment characteristics. Absolute photodetachment cross sections, accurate to a factor of 2, and the angular distributions of detached electrons are at once made a available for all atomic negative ions whose $l$, ${〈R^2〉}^{\frac{1}{2}}$, and $E$ are known, where $l$ is the angular momentum quantum number for the outermost orbital electron of the anion, $E$ and ${〈R^2〉}^{\frac{1}{2}}$ are, respectively, the electron affinity and root-mean-square radius of the neutral atom. Values of these three input parameters are readily available for most atomic anions. The model seems to encompass the major physical attributes of atomic anions required for photodetachment. Its mathematics is simple. Because of this it is suggested that the model promises applicability to more complicated systems, particularly to photodetachment from molecular negative ions, and to more complicated processes, e.g., negative-ion-neutral-atom charge exchange.

The effects of the ground-state configuration interactions and the final-state interchannel configuration interactions on the photoionization of K ii, Ca iii, Sc iv, and Ti v are examined. This calculation has shown that even at high photon energy (∼200 eV) the effect of the final-state interchannel configuration interaction remains significant as the charge state of the ions increases.

A classical theory of scattering of an electron beam by a laser standing wave (the Kapitza-Dirac effect) is presented. The prediction of the theory is in good agreement with all the experimental results which were reported independently by Bartell et al., Schwarz et al., Takeda et al., and Pfeiffer. This shows that the interaction of a free electron with coherent radiation is basically a classical process.

The theory of stimulated Thomson scattering is investigated both quantum mechanically and classically. In the interaction of a collisionless plasma with two electromagnetic waves, both with frequencies well above the plasma frequency, energy is transferred from the high-frequency wave to the low-frequency wave via stimulated Thomson scattering. This process is mediated by the nonlinear interaction of the plasma electrons with a beat wave at the difference frequency between the two waves; this beat frequency must be well above the plasma frequency. The gain coefficient for stimulated Thomson scattering is calculated both quantum mechanically and classically, and identical results are obtained. The classical calculation also yields the first nonlinear term in the index of refraction due to stimulated Thomson scattering, as well as the details of the saturation of the gain and the index of refraction. The authors present explicit formulas for the gain coefficient and the index of refraction, in the unsaturated limit, for both very cold and very hot plasmas. The calculations indicate that it should be possible to detect stimulated Thomson scattering experimentally by means of polarization enhancement. In an appendix, the theory of stimulated Thomson scattering is used to treat the free-electron amplifier.

The basic conditions for the initiation of a nuclear-detonation wave in an atmosphere having plane symmetry (e.g., a thin, layered fluid envelope on a planet or star) are developed. Two classes of such a detonation are identified: those in which the temperature of the plasma is comparable to that of the electromagnetic radiation permeating it, and those in which the temperature of the plasma is much higher. Necessary conditions are developed for the propagation of such detonation waves for an arbitrarily great distance. The contribution of fusion chain reactions to these processes is evaluated. By means of these considerations, it is shown that neither the atmosphere nor oceans of the Earth may be made to undergo propagating nuclear detonation under any circumstances.

A general formula in the form of a product of irreducible tensors is derived for the magnetic multipole-multipole interaction of any order between two nonoverlapping charge distributions. These two charge centers may be separate atoms, molecules, or nuclei. In the limit of low order, the formula is shown to reduce to the conventional spin-spin (magnetic dipole-dipole) interaction. It also reduces to a two-center expansion term obtainable from the conventional spin-other-orbit interaction.