Differential cross sections for excitation of the 3s ${}_{}{}^3{}_{}{}^{}$S° and 3p ${}_{}{}^3{}_{}{}^{}$P states of atomic oxygen by electron impact are calculated in a close-coupling approximation at energies 13.87, 20, 30, and 50 eV. We include 2${\mathit{p}}^4$ ${}_{}{}^3{}_{}{}^{}$P, 3${\mathit{s}}^{5,3}$S°, 3${\mathit{p}}^{5,3}$P, 4${\mathit{s}}^{5,3}$S°, 3 ${}_{}{}^{5,3}{}_{}{}^{}$D°, 4${\mathit{p}}^{5,3}$P, and 3s’ ${}_{}{}^3{}_{}{}^{}$D° states of atomic oxygen in the close-coupling expansion. The present results are in good agreement with the recent experiments for the resonance ${}_{}{}^3{}_{}{}^{}$P–3${\mathit{s}}^3$S° transition, but there are discrepancies between theory and experiment for the electric dipole-forbidden ${}_{}{}^3{}_{}{}^{}$P–3${\mathit{p}}^3$P transition.

The laboratory energy distribution of H+ from the dissociation of H3+ in low-keV H3+-He collisions is measured at a 0° laboratory angle. An inelastic energy loss of Q=26±2 eV has been determined for the excited states of H3+ that produce low-energy protons upon dissociation. An approximate projectile-frame energy distribution of H+ is also presented. Our results suggest that the near-zero projectile-frame energy protons are produced by either an electronic singlet excitation of the ground state of H3+ to a distribution of 2 E1′, 1 E1″, and 2 A12″, or as an alternative mechanism, a triplet excitation of H3+ to 1 E3′ accompanied by a simultaneous triplet excitation of the He target. In either case, the near-zero energy protons are produced by a three-body dissociation of the excited (H3+)*. In the case of the triplet excitation, there are no long-range correlations for the motion of the neutral H atoms. For the singlet excitation, the neutral H atoms' motion is correlated and the angle between them is near 180°. The effects of the long-range nature of the total potential between the fragments is discussed in terms of the hyperspherical coordinates.

A second-order Faddeev scattering formalism is developed for treating high-energy electron capture in nonrelativistic ion-atom collisions. The approximation to the exact capture amplitude encompasses both forward-angle and large-angle scattering. Comparison with forward-angle experimental data for protons on hydrogen and helium at energies of a few MeV shows very good agreement. The contribution of the internuclear potential to the amplitude is analyzed, and an explicit explanation of its effects as described by the eikonal transformation is given in a multiple-scattering approach. The amplitude is shown to be well behaved for singly charged incident ions.

An alternative time-dependent wave-packet method for treating three-dimensional gas phase reactive atom-diatom collisions is presented. The method employs a nonreactive body-frame wave-packet propagation procedure, made possible by judicious use of absorbing optical potentials, a novel scheme for interpolating the wave function from coordinates in one arrangement to those in another and the fact that the time-dependent Schrödinger equation is an initial-value problem. The last feature makes possible a computationally viable and accurate procedure for changing from one arrangement’s coordinates to another. In addition, the method allows the determination of S-matrix elements over a wide range of energies from a single wave-packet propagation. The determination of scattering into any particular arrangement is effectively decoupled from that into other arrangements by means of complex absorbing potentials. The method is illustrated by carrying out detailed calculations of inelastic and reactive scattering in the H+${\mathrm{H}}_2$ system using the Liu-Siegbahn-Truhlar-Horowitz potential surface.

By means of differential energy-transfer measurements, electronic excitation in ${\mathrm{Li}}^{+}$-${\mathrm{N}}_2$ and ${\mathrm{Li}}^{+}$-CO collisions has been studied at the laboratory collision energies of 70≤${\mathit{E}}_{\mathrm{lab}}$≤350 eV. Electronic excitation in ${\mathrm{Li}}^{+}$-${\mathrm{N}}_2$ collisions is observed in the energy-transfer spectra at the reduced scattering angles ${\mathit{E}}_{\mathrm{lab}}$θ≳3 keV deg. An electronically inelastic peak in the spectra observed at lower collision energies is assigned to the ${}_{}{}^1{}_{}{}^{}\mathrm{\Pi }_{\mathrm{g}}^{}{}_{}{}^{}$←X ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ transition of the ${\mathrm{N}}_2$ molecules. Analysis of the energy-transfer spectra suggests that anisotropy of the repulsive potential for the excited ${\mathrm{Li}}^{+}$-${\mathrm{N}}_2$ (${\mathit{a}}^1$${\mathrm{\Pi }}_{\mathit{g}}$) state is almost the same as that for the ground state. Predominant electronic excitation in the ${\mathrm{Li}}^{+}$-CO collisions is attributed to the ${}_{}{}^1{}_{}{}^{}\mathrm{X}$ ${}_{}{}^1{}_{}{}^{}\mathrm{\Sigma }_{}^{+}{}_{}{}^{}$ transition of the CO molecules. The excitation signal begins to appear site specifically at ${\mathit{E}}_{\mathrm{lab}}$θ≃2.1 and 4.2 keV deg in the collisions on the C-atom and O-atom sides, respectively. Regarding the specific molecular orientations γ=0° and 180° (linear configuration) at impact, electronic excitation takes place in the regions of the intermolecular distances R≤1.32 Å for the ${\mathrm{Li}}^{+}$-${\mathrm{N}}_2$ collisions, and R≤1.47 and 1.22 Å for the ${\mathrm{Li}}^{+}$-CO collisions on the C-atom and O-atom sides, respectively. These critical distances, which correspond to the potential crossing points, can be adequately explained by assuming the binary ion-atom interactions.

The dynamical elimination or reduction of macroscopic superpositions has long been of interest, particularly with regard to the quantum theory of measurement. A number of models have demonstrated this for the reduced density matrix of a system interacting with an environment. Alternatively, Ghirardi, Rhimini, and Weber [Phys. Rev. D 34, 470 (1986)] have proposed a fundamental modification of the Schrödinger equation, quantum mechanics with spontaneous localization (QMSL), which provides a master equation similar in mathematical form. In this paper we consider an isotropic environment that is elastically scattered by the system of interest with negligible momentum transfer, extending a previous result of Joos and Zeh [Z. Phys. B. 59, 223 (1985)] from small length scales to all length scales. We discuss the physical nature and relevance of the differences between our result and similar open systems calculations. We describe the mathematical similarity between our extended environmental model and the QMSL dynamics determining the QMSL parameters that allow calculations using QMSL to be used as a model for the effect of the environment. That gives us access to a number of interesting results obtained for the QMSL master equation. Finally, we discuss some experimental considerations for the purposes of detecting effective nonunitary evolution of this form.

Extremely high-lying states of atomic and molecular nitrogen ions have been observed and analyzed in the transient plasma that results from focusing a Q-switched Nd:YAG (where YAG denotes yttrium aluminum garnet) laser into a pure nitrogen atmosphere ranging in pressure from 100 to 800 Torr. During the first 10 to 80 ns after plasma ignition several states of ${\mathrm{N}}^{3+}$ can be detected. Their Stark broadened linewidth is strongly time dependent due to the rapidly changing electron density in the decaying plasma. At around 20 to 40 μs after plasma ignition, rotationally resolved emission in the first negative system of ${\mathrm{N}}_2^{+}$, ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{u}}^{+}{}_{}{}^{}$→X ${}_{}{}^2{}_{}{}^{}\mathrm{\Sigma }_{\mathrm{g}}^{+}{}_{}{}^{}$ indicates a rotational and vibrational temperature of about 9500 K. No significant interference from the second positive system ${\mathit{C}}^3$${\mathrm{\Pi }}_{\mathit{u}}$→B ${}_{}{}^3{}_{}{}^{}\mathrm{\Pi }_{\mathit{g}}^{}{}_{}{}^{}$ of the neutral molecule is observed. Under these conditions rotational levels up to N’=112 in the R branch of the (0,0) band have been identified. In this band, new perturbations at around N’=82 and 95 due to the v=12 and 13 vibrational levels of the ${\mathit{A}}^2$${\mathrm{\Pi }}_{\mathit{u}}$ state are reported.

The approximate constant of motion introduced previously for the description of a charged system in a homogeneous magnetic field is interpreted physically as the kinetic momentum of the collective motion. The algebra satisfied by this operator and by the exact constants of motion describes the behavior in a magnetic field of a single particle possessing the total charge of the system. With this algebra, we generalize the approximate constant of motion and obtain a family of operators depending on arbitrary parameters. Canonical transformations based on these new operators separate the Hamiltonian into collective, internal, and coupling terms. These terms take the same form for charged and neutral systems although the collective energy represents different physical behaviors. The coupling between the internal and collective motions is small for some choices of the parameters if at least one particle is much heavier than the other ones.

We report isotope shifts for eight transitions in Kr I for all the stable isotopes and hyperfine constants for the 1s5, 2p9, 2p8, 2p7, 2p6, 2p4, 2p3, 3p9, and 4d4′ states in Kr83. We used continuous-wave single-frequency lasers to perform resonance ionization on an atomic beam of krypton atoms in the metastable 1s5 and 1s3 states of the 4p5 5s configuration. Our results agree well with previous work and with calculations of the hyperfine constants for Kr83 in the 4p5 5p states.

The generalized reduced-potential curve (GRPC) is defined and analyzed. A special form of the GRPC formula is defined with respect to the reduced-potential curve (RPC) employed previously (parametrized formula). It is shown that the definition of the reduced potential used by Ferrante et al. [Phys. Rev. Lett. 50, 1385 (1983)] and Tellinghuisen et al. [Phys. Rev. A 39, 925 (1989)] is equivalent to the old definition of Frost and Musulin (FM) [J. Am. Chem. Soc. 76, 2045 (1954)] that is obtained from the GRPC as a limit case. It is further shown that the FM reduced potential cannot be used for a systematic comparative study of the potentials of diatomic molecules (which, however, may be successfully made in the RPC scheme), nor can the FM formula be employed to obtain accurate approximations of the potentials. On the other hand, it is demonstrated by a series of examples that very accurate approximation methods for the extensions of the potentials may be defined with the use of the GRPC formula in the framework of the RPC scheme. A parametrized RPC formula appears to be a good GRPC formula: For the inner wing, the one-parameter approximation already leads to a degree of accuracy that seems satisfactory also to a spectroscopist (limit of error in the internuclear distance less than 0.001 Å). One-parameter approximations of potentials published previously are evaluated and shown to have reached a satisfactory degree of accuracy also in the outer wing (limit of error in energy less than 3 ${\mathrm{cm}}^{\mathrm{-}1}$). The GRPC method is also employed to obtain an essentially more accurate approximation from theoretical ab initio calculated potentials. The potentials obtained with the aid of the GRPC method may then be used for the calculation of the spectra.

We show that the zero- and nonzero-nuclear-spin isotopes of Ba and Sr can be excited and ionized at different rates by sequential absorption of radiation from two pulsed laser beams. The selective excitation takes place in a J=0←J=1←J=0 energy-level scheme (where J is the electronic angular momentum), which, depending on the relative polarization of the laser beams, gives totally destructive interference in the absorption rate to the upper J=0 state of a zero-nuclear-spin atom, or a finite but time-dependent rate for population of the upper state for an atom with nonzero nuclear spin. A theoretical explanation of the effect shows the alignment of the nuclear spin as well as the population of the upper state to be time dependent. Isotope ratios were measured in Ba and Sr as a function of laser polarization and delay time, and compared with theory.

Absorption and fluorescence cross sections of ${\mathrm{BF}}_3$ were measured in the 45–113-nm region. Partial ionization cross sections are derived from the absorption cross section and the known branching ratios and then compared with theoretical calculations. The absorption spectrum shows many vibrational progressions and broad bands that are attributed to the Rydberg and/or valence transitions. Fluorescence from excited ${\mathrm{BF}}_2^{\mathrm{*}}$ is observed from photoexcitation of ${\mathrm{BF}}_3$. The fluorescence quantum yield shows two repulsive excited states that give maximum yields of 34% at 88 nm and 20% at 96 nm. These two states produce four ${\mathrm{BF}}_2^{\mathrm{*}}$ emission bands that are distinguished by different fluorescence spectra and radiative lifetimes. The photoexcitation processes that lead to fluorescence and ionization are discussed.

The dependence of f values on the reciprocal of the nuclear charge in the sequence is discussed on the basis of quantum-defect computations through three different formulations of the transition dipole moment. Several simple systems are studied.

We report results of a survey of microwave transition frequencies between S,P, andD singlet and triplet Rydberg states of calcium in the range n=22–55 . The accuracy of the measurements is approximately one part in ${10}^6$. The data have been analyzed using generalized energy expansions for the quantum defects, with the exception of the 4snd ${}_{}{}^1{}_{}{}^{}$${\mathit{D}}_2$ series, for which numerical values of the quantum defects are presented.

The behavior of the Floquet eigenvalues of a zero-range potential in a circularly polarized radiation field is studied over the whole range of frequencies. Convergent Rayleigh-Schrödinger perturbation series for these eigenvalues are generated to high order, and the dependence of the radius of convergence on the frequency is also discussed.

A reaction of the form Ai+Ai′′+ħΩ→Af+Af′′ has been referred to as light-induced collisional energy transfer (LICET). In such a reaction, atoms A and A′ collide in the presence of a radiation field and absorb a photon during the collision, taking them from initial states (Ai,Ai′′) to different final states (Af,Af′′). We calculate the final-state magnetic polarization produced in LICET for detunings Δ=[(Ef+Ef′)-(Ei+Ei′+ħΩ)]/ħ in the quasistatic wing: that is, for |Δ|τc≫1, where τc is the collision duration. Our results are compared with analogous depolarization rates for so-called “optical” collisions (reactions of the form Ai+Ai′′+ħΩ→Ai+Af′′). Similarities and differences between the LICET and “optical” collision theories are noted. Final-state LICET magnetic-state polarization is evaluated for a number of different A-A′ level schemes, assuming a dipole-dipole collisional interaction. Our results are shown to be in good agreement with experiment [A. Débarre, J. Phys. B 15, 1693 (1982)].

It is usually assumed that a balanced homodyne detector measures a variable called the quadrature phase amplitude of a signal field. We examine this assumption by obtaining analytic expressions for the probability statistics for the output of such a detector for a single-mode signal with both signal and local oscillator treated quantum mechanically. We investigate the conditions under which the statistics of the quadrature phase are reproduced in the actual output of the detector. We show that the most obvious condition—that the number of quanta in the local oscillator be much larger than the number in the signal—is not sufficient to ensure that a balanced homodyne detector acts like an ideal detector of quadrature phases. Furthermore, we obtain the explicit conditions that are necessary and sufficient to reproduce the interference features in the homodyne statistics of a superposition of coherent states.

The near-threshold behavior of a single-mode ${\mathrm{CO}}_2$ laser has been investigated by applying a linear modulation to the excitation current. The associated delayed bifurcation has been characterized in terms of first-passage-time distributions for different sweep rates. A theoretical model provides good agreement with the experimental data. In particular, we are able to assign the initial photon number below threshold.

We show that the master equation describing the dissipative evolution of a bosonic quantum system coupled to a phase-sensitive reservoir may be reduced to a standard form of dissipation for a thermal reservoir by canonical transformations. The solution to the master equation for complex phase-sensitive interaction induced, for example, by broadband squeezed light, may then be obtained by a transformation from the known solutions for the simpler thermal case. We show that canonical transformations have a particularly useful form when describing the evolution of quantum dissipative systems in phase space using the Wigner function. We illustrate these ideas with two phase-sensitive dissipative problems: that of the correlated-emission laser and of decay induced by a broadband squeezed vacuum field.

Incoherence introduced in two-path experiments by interactions with scatterers in thermal equilibrium is examined with an energy-momentum approach previously used for the Mössbauer effect. Oscillations in intensity with variations in the magnetic flux are shown to be insensitive to random phase changes in the individual scattering amplitudes. Inelastic incoherent scattering may be suppressed when there are a large number of scatterers. A small loss of phase coherence negligible in cases of practical interest can occur even via elastic scattering, which does not perturb the environment. The temperature dependence of the loss of interference, analogous to the Debye-Waller factor, may be tested by experiment.