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I welcome the long-overdue recognition of medical futility represented by the contributions of Koch, et al., Miles, and Dew, although I would be more comfortable with using the more global (and optimistic) term of “beneficence.” However labeled, the notion that medical treatment decisions are primarily that—medical decisions—is a far more appropriate starting point in both law and ethics than the customary departure point of patient autonomy. This is particularly true in cases in which the patient is not competent, and prior expressions of intent are remote, vague, or otherwise unreliable. Despite such flaws, prior statements have been invested with a talismanic quality, permitting avoidance of the genuine moral issues of duty and benefit that are presented by every severely ill and incompetent patient.The rise of patient autonomy may actually have had less to do with genuine concern for the liberty of the patient than with the moral vacuum created by an excessively pluralistic view of medical ethics. Courts in particular have fallen out of the habit of a priori moral reasoning, replacing this discipline with balancing tests of asserred personal and governmental power.

We present a numerical solution for one-parameter linear Jahn-Teller coupling as it affects the full vibronic energy level spectrum of the T⊗τ problem. The Franck-Condon distribution of spectral intensities for the electronic transition from a totally symmetric originating state is characterized as a function of the linear coupling strength.

A rotationally resolved one‐photon threshold photoionization spectrum of jet‐cooled water (H2O and D2O) has been obtained by pulsed field ionization of extremely high‐n Rydberg states. Observed spectral intensities for both vibrationless (0,0,0) and vibrationally excited (1,0,0) water cation show a strong propensity for ΔN=0, ±1 transitions. In contrast to earlier work on O2 and HCl, the lack of large ΔN transitions suggests that ionization occurs with only small angular momentum transfers between the core and photoelectron. The presence of both type A and type C ‘‘symmetric top’’ transitions varies from the conclusions of a recent MQDT analysis of H2O photoionization, which predicts only type C transitions. Rotational analysis of the spectra yields improved ionization potentials for both H2O and D2O. The ionization potential of the (1,0,0) vibrational level provides a direct measurement of the symmetric stretch fundamental in H2O+ which is in excellent agreement with an earlier indirect determination. Ro...

Pulsed field ionization (PFI) has been used in conjunction with a coherent VUV source to obtain high-resolution threshold photoelectron spectra for the (000), (010), (020), and (100) vibrational states of the N2O(+) cation. Simulations for the rotational profiles of each vibronic level were obtained by fitting the Buckingham-Orr-Sichel equations using accurate spectroscopic constants for the ground states of the neutral and the ion. The relative branch intensities are interpreted in terms of the partial waves of the outgoing photoelectron to which the ionic core is coupled and in terms of the angular momentum transferred to the core.

Multiresonant, ionization‐detected absorption spectra of autoionizing ns and nd Rydberg states converging to the (200) and (300) vibrational states of the NO+2 core show unexpectedly broad resonances for many states nominally requiring Δv=−2 and −3 vibrational transitions in the core to energetically achieve electron ejection. The resonances observed do not show evidence of significant predissociation, implying that the autoionization process is primarily vibrational. Perturbed line shapes and the presence of many resonances not clearly associated with the assigned sσ, dσ, and dπ series indicate extensive vibronic coupling with other Rydberg vibrational manifolds. A particularly broad feature at a total energy of 78 720 cm−1 appears in spectra scanned both from the (200) and (300) levels of the 3pσ state. This energy falls just below the threshold for forming NO+2 in the vibrational state (100), and the broad features that appear at this point in the higher vibrational manifolds can be identified as compo...

We explore the problem of an orbitally triple degenerate electronic state coupled with a doubly degenerate vibrational mode, for a molecule within the T d rigid geometrical point group, using exact as well as numerical methods. Franck-Condon overlap integrals are worked out and are displayed as a function of linear coupling parameter. The effect of inclusion of quadratic coupling terms on the eigenvalue and intensity distribution are compared with the linear case.

Ultraviolet two‐photon photoselection, followed by visible one‐photon absorption is applied to HCl to record the first double‐resonant spin–orbit autoionization spectrum of a hydrogen halide, and the first rotationally resolved such spectrum of HCl. The J=2 level of the F 1Δ2(v=0) Rydberg state serves as the intermediate two‐photon resonance. The ionization‐detected absorption spectrum from this initial state, scanned across the 634 cm−1 interval between the lower 2Π3/2 and upper 2Π1/2 thresholds, shows a complex system consisting of hundreds of sharp lines converging to the accessible rotational limits of the upper spin–orbit threshold. The complexity of the spectrum is attributed to the relaxed selection rules associated with dipole transitions from a state in Hund’s case (a) to a manifold approaching Hund’s case (e), in concert with the irregularities expected for angular momentum coupling intermediate between the limits of case (c) and case (e). A simple case (e) fit over the central portion of the sp...

We report the spontaneous formation of a plasma from a gas of cold Rydberg molecules. Double-resonant laser excitation promotes nitric oxide, cooled to 1 K in a seeded supersonic molecular beam, to single Rydberg states extending as deep as 80 cm$^{-1}$ below the lowest ionization threshold. The density of excited molecules in the illuminated volume is as high as 1 x 10$^{13}$ cm$^{-3}$. This population evolves to produce prompt free electrons and a durable cold plasma of electrons and intact NO$^{+}$ ions., 4 pages (two column) 3 figures; smaller figure files, corrected typos

Three‐color, triple‐resonance ionization‐detected absorption spectra of the autoionizing (010) s and d states of NO2 are presented and compared with similar spectra of the (100) and (110) manifolds. The (010) states are well described by Hund’s case (d), and exhibit evidence of vibronic coupling with other vibrational manifolds. The laser limited linewidths of the (010) resonances show autoionization by ν2 to be slower than autoionization via ν1 by a factor of at least 30. The mode dependence of the autoionization rate can be explained by a model established some time ago for diatomics that connects the Rydberg‐electron‐cation‐core coupling dynamics with the time‐dependent core charge distribution associated with each vibrationally excited state. Simple calculations, which focus on the monopolar components of the core‐vibrational dynamic multipole potentials, agree qualitatively with the experimental results. A large signal increase at the (010) vertical threshold evidences significant decay through predissociation. Comparison with the (100) and (110) vertical thresholds suggests that, in addition to coupling less effectively to the ionization continuum, excitation in ν2 promotes dissociation.

Ionization‐detected absorption spectra of the (100) vibrationally autoionizing states of NO2 have been recorded from double‐resonantly prepared N’=1 and N’=7 rotational levels of the 3pσ 2Σ+u (100) Rydberg intermediate state. Photoselection associated with three‐color triple‐resonant absorption spectroscopy resolves single rotational lines in discrete electronic states that lie above the adiabatic ionization threshold at total energies as high as 78 800 cm−1. Most features observed can be assigned to sσ, dσ, and dπ series converging to the (100) vertical threshold. Identified transitions extend over an interval of principal quantum numbers ranging from 9 to more than 40. A fourth short progression of sharp transitions is assigned as a segment of a g series. The complete spectrum of (100) transitions is modulated in intensity by a sequence of dips that form a series of states, recognized as pσ and pπ, converging to the (110) threshold. Evidence is cited for a mirror‐image effect in autoionizing rates, wher...

In this study, the feasibility of using Raman spectroscopy as a fast, non-invasive, non-destructive technique to monitor crystallization and polymorphic transformations during freeze-drying is assessed using mannitol as the model compound. In-line process monitoring was achieved by interfacing a Raman spectrometer with a fiber-optically coupled, long-working-distance probe to a freeze-drier. By analyzing the process data using principal component analysis, it was possible to extract valuable information pertaining to ice and mannitol crystallization points, the polymorphic form of mannitol, and dehydration of the mannitol hydrate. In conclusion, Raman spectroscopy is a potentially useful technique to monitor physical changes during freeze-drying.

Zero-kinetic-energy (ZEKE) photoelectron techniques have now become new tools of physical chemistry that go far beyond the measurement of the spectra of molecular ions. The unprecedented resolution of the ZEKE method [8, 9], which is essentially limited by the laser bandwidth, has already led to many new and exciting applications in chemical physics and chemistry within the last few years. The rapid expansion of this method to a number of very active laboratories clearly suggests that this trend can be expected to continue [24- 47].

Analytical techniques for rapid and nondestructive content uniformity determination of pharmaceutical solid dosage forms have been studied for several years in an effort to replace the traditional wet chemistry procedures, which are labor intensive and time consuming. Both Raman spectroscopy and near-infrared spectroscopy have been used for this purpose, and predictability errors are approaching those of the traditional techniques. In this study, a low-resolution Raman spectrometer was utilized to demonstrate the feasibility of both rapid at-line and on-line determination of tablet content uniformity. Additionally, sampling statistics were reviewed in an effort to determine how many tablets should be assayed for specific batch sizes. A good correlation was observed between assay values determined by high-performance liquid chromatography and Raman analysis. Due to rapid acquisition times for the Raman data, it was possible to analyze far more samples than with wet chemistry methods, leading to a better statistical description of variation within the batch. For at-line experiments, the sampling volume was increased by rotating the laser beam during the acquisition period. For the on-line experiments, the sampling volume was increased by sampling from a stream of tablets moving underneath the Raman probe on a conveyor system. Finally, an approach is proposed for monitoring content uniformity immediately following the compaction process. In conclusion, Raman spectroscopy has potential as a rapid, nondestructive technique for at- or on-line determination of tablet content uniformity.

Optical-optical-optical triple-resonance spectroscopy of (11)BH isolates high Rydberg states that form series converging to rotational state specific ionization potentials in the vibrational levels of (11)BH(+) from nu(+)=0 through 4. Limits defined by a comprehensive fit of these series to state-detailed thresholds yield rovibrational constants describing the X (2)Sigma(+) state of (11)BH(+). The data provide a first determination of the vibrational-rotational interaction parameter alpha(e)=0.4821 cm(-1) and a more accurate estimate of omega(e)=2526.58 cm(-1) together with the higher-order anharmonic terms omega(e)x(e)=61.98 cm(-1) and omega(e)y(e)=-1.989 cm(-1). The deperturbation and global fit of series to state-detailed limits also yield a precise value of the adiabatic ionization potential of (11)BH of 79 120.3+/-0.1 cm(-1), or 9.810 33+/-1x10(-5) eV. High precision is afforded here by the use of graphical analysis techniques, narrow-bandwidth laser systems, and an analysis of newly observed, high principal quantum number Rydberg states that conform well with Hund's case (d) electron-core coupling limit.

The spectroscopy of molecular Rydberg states provides a powerful link between the electronic structure of molecular excited states and the dynamics of a variety of important electron-cation scattering interactions including for example collisional and associative ionization, photoionization, dielectronic and dissociative recombination, and various forms of autoionization. A key element in this link is the interpretative framework provided by Multichannel Quantum Defect Theory (MQDT) [1, 2]. This treatment ties electron-cation scattering amplitudes to potential energy surface features of the cation-electron collision complex. Its strength lies in the systematic explanation of many thousands of spectral features and underlying state-to-state interactions in terms of small number of accurately determined details of the electronic structure of a system. Following its initial extension from atoms [3], MQDT has grown to become an established tool for understanding the excited-state structure and dynamics of a large number of diatomic molecules.

We report a novel approach to the measurement of colored tablet coating thickness, which employs Raman spectroscopy with univariate and multivariate data analysis. Our results suggest that Raman sensing can serve as a viable non-invasive means to quantify tablet coating thickness in the presence of a fluorescent ingredient in the coating formulation (food colorant Alphazurine FG or D&C Blue No. 4). This study comparatively tests the advantage of several data transformation approaches, including mean centering, standard normal variate, and Savitzky–Golay smoothed second derivative as means of improving predictive models in the presence of fluorescence. By application of the partial least squares (PLS) calibration algorithm to establish optimum covariance between transformed spectral data and measured tablet coating thicknesses, we have been able to create predictive models with calibration errors as small as 4 μm for a training set that spans colored coating thicknesses from 50 to 151 μm.

This report describes the results of a program of research on the thermochemistry, spectroscopy and intramolecular relaxation dynamics of the combustion intermediate, HCO. We prepare this radical from acetaldehyde as a photo-precursor in a differentially pumped laser-ionization source quadrupole mass spectrometer. Using a multiresonant spectroscopic technique established in our laboratory, we select individual rotational states and overcome Franck-Condon barriers associated with neutral-to-cation geometry changes to promote transitions to individual autoionizing series and state-resolved ionization thresholds. Systematic analysis of rotational structure and associated lineshapes provide experimental insight on autoionization dynamics as input for theoretical modeling. Extrapolation of series, combined with direct threshold-photoelectron detection, yield precise ionization potentials that constitute an important contribution to the thermochemical base of information on HCO.

A two-color $(3+{1}^{\ensuremath{'}})$ pump-probe scheme is used to create Rydberg wave packets in krypton atoms. The ac-Stark shift, caused by the high intensity pump pulse, allows access to states with principal quantum numbers $n=5--10$ over a broad energy range. States shifted by as much as $3000\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ during the pump pulse are coherently excited, resulting in wave-packet superpositions of field free states. By resolving the kinetic energy of the photoelectrons produced in the ionization probe step, numerous quantum beats are resolved and assigned. In addition, the energies of four previously unmeasured $g$ states are determined.

Millions of end-of-life electronic components are retired annually due to the proliferation of new models and their rapid obsolescence. The recovery of resources such as plastics from these goods requires their disassembly. The time required for each disassembly and its associated cost is defined by the operator's familiarity with the product design and its complexity. Since model proliferation serves to complicate an operator's learning curve, it is worthwhile to investigate the benefits to be gained in a disassembly operator's preplanning process. Effective disassembly process design demands the application of green engineering principles, such as those developed by Anastas and Zimmerman (Environ. Sci. Technol. 2003, 37, 94A-101A), which include regard for product complexity, structural commonality, separation energy, material value, and waste prevention. This paper introduces the concept of design symbols to help the operator more efficiently survey product complexity with respect to location and number of fasteners to remove a structure that is common to all electronics: the housing. With a sample of 71 different computers, printers, and monitors, we demonstrate that appropriate symbols reduce the total disassembly planning time by 13.2 min. Such an improvement could well make efficient the separation of plastic that would otherwise be destined for waste-to-energy or landfill. The symbolic methodology presented may also improve Design for Recycling and Design for Maintenance and Support.

We have applied optical-optical-optical triple resonance spectroscopy to resolve a system of high Rydberg states in BH that serves quantitatively to characterize a fundamental example of electron-orbital-cation core rotational coupling. The third-color ionization-detected absorption spectrum originating from the photoselected 3s B 1 Σ + Rydberg state with vibrational and total angular momentum quantum numbers, v' = 1 and N = 0 consists entirely of vibrationally autoionizing resonances for which final N = 1 that converge in series to the BH + v t = 1 rotational limits, N + = 0, 1, and 2. For series with l = 1 converging to N + = 0 and 2, Rydberg orbital and rotational angular momenta couple to systematically perturb level energies and distribute lifetime in a well-isolated two-channel rotronic interaction that spans hundreds of wave numbers.

A Rydberg gas of xenon, entrained in a supersonic atomic beam, evolves slowly to form an ultracold plasma. In the early stages of this evolution, when the free-electron density is low, Rydberg atoms undergo long-range -mixing collisions, yielding states of high orbital angular momentum. The development of high- states promotes dipole–dipole interactions that help to drive Penning ionization. The electron density increases until it reaches the threshold for avalanche. Ninety μs after the production of a Rydberg gas with the initial state, , a 432 V cm−1 electrostatic pulse fails to separate charge in the excited volume, an effect which is ascribed to screening by free electrons. Photoexcitation cross sections, observed rates of -mixing, and a coupled-rate-equation model simulating the onset of the electron-impact avalanche point consistently to an initial Rydberg gas density of .

Moshe Shapiro, a pioneer in the area of quantum control of molecular dynamics, whose research opened new pathways for directing the course of chemical reactions and creating matter in unique, often quantum-specified states of aggregation, died on 3 December 2013 in Rehovot, Israel. He was 69 years old. Professor Shapiro is perhaps best known for his work with Paul Brumer of the University of Toronto. In 1986, the pair developed theoretical models predicting the control of unimolecular reactions following excitation by coherent fields of laser light. The reaction dynamics community immediately recognized the Brumer–Shapiro approach as distinct from ideas prevailing at the time to use sequences of short laser pulses timed to impulsively direct wavepacket motion in molecules. Many experimental groups devised strategies to apply this principle of phase control of molecular dynamics, and the results provided some of the earliest and most robust demonstrations of coherent control. The field has matured since to employ emerging electro-optic techniques to shape the phase and frequency characteristics of laser sources in time, and achieve degrees of control that rely simultaneously on interference and impulse. This is well demonstrated by the technique of step-wise adiabatic passage, introduced by Shapiro's group at the University of British Columbia, which enables the controlled transport of an ensemble of molecules to a selected level of excitation, and ultracold atoms to bound, ground-state molecules. Shapiro introduced a number of other new ideas to chemical dynamics. Working with Richard Bersohn, he performed early quantum scattering calculations that traced the multidimensional relaxation of potential energy in the photofragmentation of methyl iodide leading to vibrational excitation of the umbrella bend of the methyl radical product. He also described general conditions characterizing chaos in an isolated energy eigenstate, developed a theory for controlled photon induced symmetry breaking to form chiral products from achiral precursors, and showed how to use phase-coherent laser excitation to launch directional currents in semiconductors, in the absence of bias voltage. He has also contributed to important advances in laser catalysis, quantum computing and decoherence, transition state spectroscopy, potential inversion and wavefunction imaging, the theory of strong field phenomena in atoms and molecules, quantum theory of elementary exchange reactions and foundations of quantum mechanics. His most recent research focused on the control of molecular, atomic, and photonic processes with coherent light, quantum pattern recognition, coherent chiral separation and the coherent suppression of spontaneous emission, decoherence and other decay processes. At UBC, Moshe is remembered for his perceptiveness, broad vision and collegiality. 'One day he came to a group meeting with the idea of a solar-pumped living laser,' said physics colleague, Valery Milner. 'After thinking about this for two months, we designed an experiment using a random laser cavity that produced gain with milliwatts of pumping power applied to a fluorescent protein. We have now only to get lasing with the bacterium we engineered to express this protein.' Moshe studied for his PhD guided by Professor Raphael D Levine, in theoretical chemistry at the Hebrew University, focusing on photodissociation and molecular collisions. In 1970, he moved to Harvard University as a postdoctoral fellow, where he worked in reaction dynamics with Martin Karplus, a 2013 Nobel laureate in chemistry. In 1972, Moshe joined the faculty of the Department of Chemical Physics at the Weizmann Institute. There, he served as a department chair and was named the Jacques Mimran Professor of Chemical Physics. In 2002, he was appointed to a Canada Research Chair in Quantum Control in the Department of Chemistry at UBC. He won the Willis E Lamb Medal for achievements in the Physics of Quantum Electronics (2007), the John C Polanyi Award of The Canadian Society of Chemistry (2011), the Israel Chemical Society Award (2001), the Michael Landau Prize (1985), Lisa Meitner–Alexander von Humboldt Research Award (1995), the Weizmann Prize of the city of Tel Aviv (1999), the Kolthoff Prize of the Technion (1998) and the Sacks and Yeroslawski awards of the Weizmann Institute. He was elected Fellow of the American Physical Society (2004) and Fellow of the UK Institute of Physics (2004). Writing with Paul Brumer in 'Quantum Control of Molecular Processes,' Moshe laid the groundwork for using coherent light to direct the outcome of chemical transformations. 'What determines the final outcome of a photodissociation process?' he asks. 'The linear time dependence of the Schrodinger equation guarantees that the probability of future events is completely determined by the probability of past events...By identifying attributes of the quantum state at earlier times we learn what is required to alter—that is control—system dynamics in future times.' The chemical physics community has lost a guiding light in the field of quantum control. Moshe served on the Editorial Board of the Journal of Physics B from 2003 to 2008 and on its Editorial Advisory Board from 2009 to 2013.

The dissociation of excited state ${\mathrm{Br}}_{2}$ is probed with the novel technique of ultrafast soft x-ray photoelectron spectroscopy. Excited ${\mathrm{Br}}_{2}$ molecules are prepared in the dissociative $^{1}\ensuremath{\Pi}_{u}$ state with 80 fs, 400 nm pulses, and a series of photoelectron spectra are obtained during dissociation with pulses of soft x-ray light (47 nm, 26.4 eV, 250 fs). The formation of Br atoms is readily detected and the data support an extremely fast dissociation time for ${\mathrm{Br}}_{2}$ on the order of 40 fs. Amplitudes of the pump-probe features reveal that the ionization cross section of atomic Br at 47 nm is $\ensuremath{\sim}40$ times larger than that of ${\mathrm{Br}}_{2}$.

Ionization-detected absorption spectra of autoionizing Rydberg series converging to (100), (010), (0200), and 0220) vibrational states of NO2+ have been recorded in three-color triple resonant excitation. Resonances associated with decay by relaxation in symmetric stretch are found to be much broader than those observed for the core excited in one quantum of the bending vibration, consistent with earlier findings on mode- specificity of vibrational autoionization in this system. Series excited in (0200), on the other hand, are found to behave much more like (100) than (010), indicating that the bending specificity that characterizes the fundamental is lost in the overtone. This loss of mode specificity with increasing vibrational energy is ascribed to (100) - (0200) Fermi resonance in the NO2+ core, exemplifying how even small vibrational coupling can redirect mode-specific fragmentation pathways in polyatomic molecules.© (1995) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

We present a kinetic model based on coupled rate-equation simulations that accounts for state-detailed rate processes in the evolution of a molecular Rydberg gas to plasma. Calculations support a steady-state picture of Rydberg predissociation and its contribution to plasma dissipation. Inelastic collisions of electrons with Rydberg states efficiently transfer energy from and to the thermal bath of free electrons, giving rise to quasi equilibria of relatively high temperature. Dissipative effects that remove low-n population change the time course of this heating. Including statistically sampled channels of Rydberg predissociation with n- and l-dependent lifetimes slows the relaxation to quasi equilibrium and retards the initial electron temperature increase. At later times, the dissociative loss of low-n population displaces this quasi equilibrium leading to continuous electron heating. Dissociation products appear at a rate that is controlled initially by the rate of Rydberg relaxation to quasi equilibrium. Thereafter, the overall rate at which the total dissociation consumes neutral molecules determines the decay rate for all levels. Simulations predict a total predissociation rate that is smaller than the initial rate of direct electron–ion dissociative recombination. At later times, residual predissociation displays an apparent first-order decay with a rate constant that fits well with experimental observations.

Using optical-optical-optical triple-resonance spectroscopy, we assign rotational levels with N = 0-5 in the vibrationless, lower-n, p Rydberg states of (11)BH. We apply the Hill and Van Vleck formulation for energy levels with l = 1 in a Hund's case intermediate between (b) and (d) to gauge the energy separating (1)Π and (1)Σ(+) states with zero rotation for n = 4-11. This energy difference, A(l, ξ), represents the strength of the coupling, ξ, between the electron orbital angular momentum, l, and the internuclear axis, which determines the Λ-splitting constant, q(0). The np series exhibits a large q(0) that increases monotonically with n to reach a magnitude similar to the rotational constant, B(0), by n = 9. For higher principal quantum numbers, Λ ceases to be a good quantum number, and l-uncoupling becomes virtually complete for n > 10.

Coupled rate equation calculations demonstrate that the variational rate theory models for the three-body electron–electron–ion scattering dynamics associated with ultracold plasma evolution scale with density in accordance with the classical mechanics of a Coulomb system. Completeness of scaling requires a broad domain of Rydberg levels over which a quasi-equilibrium can be established. For given initial conditions, the predicted evolution of electron temperature with time changes with the choice of nmax, i.e. the highest Rydberg orbital populated by three-body recombination. But, if the criterion that defines nmax scales with density, then the results scale. Molecular dynamics calculations distinguish bound Rydberg states by an electron–ion distance criterion, Rmax, which is represented in scaled coordinates by Rmax = rmaxaws, where aws represents the Wigner–Seitz radius and rmax is chosen arbitrarily. The rate equation calculations best conform with the output of molecular dynamics simulations for values of nmax defined by a thermal criterion, . In a hydrogenic limit, the thermal criterion equates with a scaled distance criterion when rmax = Γe/2, where Γe = e2/4πϵ0awskBTe describes the degree of electron correlation. Molecular dynamics simulations conventionally attenuate the Coulomb potential by means of a term, C, . Reference to rate equation calculations suggests a connection between the soft-core term, C, and nmin, the lowest Rydberg level considered in the relaxation of the plasma to a quasi-steady state.

The potential of using interferences between transition amplitudes for the coherent control of photoionization rates and of asymmetric photoelectron angular distributions has been demonstrated previously. Current efforts in our laboratories are directed toward control of photoionization of NO, and on control of photoionization channels in atomic barium. This latter system is, of course, much simpler than a molecular system, and thus may provide better insight into the mechanisms involved. We will discuss our investigations of the effects of nonlinear coupling, absorption, and dispersion of the laser beams on their propagation through dense media, as observed via interference effects. Laser band structure effects and the effect of Doppler broadening will also be discussed.© (1994) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.

State‐selected delayed pulsed‐field threshold photoionizationspectra of HCl and DCl are recorded in double‐resonant transitions through the F ^1Δ, E ^1Σ^+, and g ^3Σ^− states of the 4pπ Rydberg configuration. Comparison of observed rotational line strengths with calculated spectra, as well as with available time‐of‐flight photoelectron spectra, provides useful insight on the influence of spin–orbit and rotational autoionization on delayed pulsed‐field threshold photoionization of HCl. Spin–orbit and rotational autoionization are seen to dramatically reduce the ion rotational intensity associated with the upper spin–orbit level of the ion.

Many people who are mobility impaired are incapable, for a variety of reasons, of using an ordinary wheelchair. These people must rely on either a power wheelchair, which they control, or another person to push and guide them while they are in an ordinary or power wheelchair. Power wheelchairs can be difficult to operate. If a person has additional disabilities, either in perception or fine motor control of their hands, a power chair can be difficult or impossible for them to use safely. Having one person push and guide a person who is mobility impaired is very expensive, and if the disabled person is otherwise independent, very inefficient and frustrating. This paper describes a low-cost robotic addition to a power wheelchair that assists the rider of the chair in avoiding obstacles, going to pre-designated places, and maneuvering through doorways and other narrow or crowded areas. This system can be interfaced to a variety of input devices, and can give the operator as much or as little moment by moment control of the chair as they wish.

A time-of-flight photoelectron spectrometer is oriented coaxially with a pulsed molecular beam to detect high Rydberg states of HCl with lifetimes as long as 7 \ensuremath{\mu}s. Two classes of such states are found. Delayed extraction following double-resonant excitation field-ionizes Rydberg states of very high principal quantum number (n\ensuremath{\ge}100) that converge to successive rotational limits for producing ${\mathrm{HCl}}^{+}$, effectively yielding a rotationally resolved threshold photoelectron spectrum. Surprisingly, excitation under more rigorously field-free conditions (100 mV/cm) produces additional resonances which can be assigned to series of long-lived Rydberg states extending to principal quantum numbers as low as 10. The lower-principal-quantum-number resonances isolated by their long field-free lifetimes appear to constitute a high-angular-momentum nonpenetrating subset of the autoionizing Rydberg series that converge both to accessible rotational levels of the upper $^{2}\mathrm{\ensuremath{\Pi}}_{1/2}$ threshold and excited rotational limits of the $^{2}\mathrm{\ensuremath{\Pi}}_{3/2}$ ground state of ${\mathrm{HCl}}^{+}$.

Progress is described in a three-year program of research supported by AFOSR under the High-Energy-Density-Matter (HEDM) initiative. A laser-crossed molecular beam apparatus was constructed which is equipped to probe unique high- energy excited states by: (1) directly detecting anion photoproducts of charge- transfer intermediate excited states; (2) determining internal state distributions following photoionization of high-energy intermediates by time-of- flight photoelectron spectroscopy; and (3) characterizing ion-fragment disturbutions by time-of-flight mass spectroscopy. This instrument was employed in combination with a second, quadrupole molecular beam system to complete a set of experiments exploring structural and dynamical properties of high-energy matter. AFOSR supported experiments have detected anions arising from energetic charge-transfer configurations of monomeric HC1. Additional work on the same molecule, has probed intermediate-state effects on ion-fragment branching rations, and, by double-resonance, characterized the dynamics of rotationally state selected spin-orbit autoionization.

Mass spectrometry is undergoing rapid development, especially with the extension of its range into the hundreds of kilodaltons, the emergence of the quadrupole ion trap as a high-performance instrument, and the development of techniques for recording three-dimensional spectra. These advances are summarized in this review; in addition, the power of the combination of lasers and mass spectrometers is given particular emphasis. Their combination has contributed recently to chemical dynamics, to the study of cluster structure and reactivity, and to the elucidation of the properties of highly excited molecules and ions.

Optical-optical-optical triple resonance spectroscopy isolates transitions to vibrationless Rydberg states of BH with principal quantum numbers from n=7 to 50. Corresponding resonances appear in the excitation spectrum of excited boron atoms produced by the dissociative relaxation of these states. The decay to neutral products occurs on a nanosecond time scale. Yet, corresponding resonances show Fano coupling widths that approach 1 cm-1. Above threshold, spontaneous ionization dominates, but line shapes match for resonances with the same electron orbital quantum numbers built on v+=0 and v+=1 cores. This striking feature-for-feature similarity in predissociation and autoionization line shapes affirms that inelastic electron-cation scattering pathways leading to electron ejection and dissociative recombination proceed through a common continuum.

We re-examine the ionization-detected ultraviolet absorption spectrum of the 3pπ 2Π←X 2A′ transition in HCO and DCO using a high-power visible laser to enhance the observation of first-photon resonant features. This technique, which we term here, assisted REMPI, significantly improves the signal-to-noise ratio of the spectrum, making many weak vibronic sub-bands visible for the first time. A comprehensive fit to the structure evident in a progression of bending levels from (000) to (040) refines the assignment of Song and Cool [X. M. Song and T. A. Cool, J. Chem. Phys. 96, 8664 (1992)] to yield a set of rotational constants that vary with K in relation to v2, together with a higher-order contribution to the Renner–Teller splitting in HCO, which is mirrored in DCO for all levels but (040). The (040) band falls at a frequency that is commensurate with that of CD stretch, and Fermi resonance between 3pπ 2Π(1000)Π and the higher-energy (040) K=1(Π) component gives rise to an added splitting that increases the...

We report the ionization-detected absorption spectra of autoionizing Rydberg states converging to the (010) vibrational level of HCO+. Sharp second-photon resonances appear in transitions from first-photon-prepared originating states that have total angular momentum (less-spin) from N′=0 to 5, selected from the Σ+ and Σ− components of the (010) band of the 3pπ2Π Rydberg state. We systematically compare spectra in order to characterize observed resonances in terms of the good total angular momentum quantum number, N. Rydberg analysis establishes the convergence of series to detailed cation-core rotational quantum numbers, N+. Observed series are found to fit well with simulations employing a limited set of constant quantum defects (δ=1.062, 0.794, 0.606, 0.253, 0.015, 0.002, −0.027 and −0.076). The strengths of observed transitions as a function of initial and final total angular momentum provide a purely experimental indication of the appropriate assignment of the approximately good orbital angular moment...

New methods for the precise (state-detailed) resolution of ionization thresholds open new vistas in photoionization dynamics, ion spectroscopy and state-selected ion-molecule reactions.

Polarized two‐photon photodissociation of NO2 in the region of 480 nm yields NO(v‘=0) with an anisotropic distribution of J. Measured polarization ratios are compared to quantum mechanical calculations for a range of expected ratios for the various isolated and mixed branches of the NO X2Π1/2→A 2Σ+ transition. Theoretical results show that main branches and their respective satellites (e.g., R11 and R21 branches) have the same transition moment directionally, though their intensities are in general different, implying that care is needed in interpreting polarization data from the mixed branches, such as (Q21+R11) or (Q11+P21), which measure the Π+ and Π− Λ doublet, respectively. Recognition of this fact is particularly important for properly separating the consideration of electron density distributions of Λ doublets from transition moment directionalities, as this has been a source of confusion in the literature. The measured results indicate that the principal two‐photon photoexcitation pathway in NO2...

We extend recent works of Berry, Simon, and others on the evolution of adiabatic wave functions in parameter spaces with nontrivial global geometry, to show the interesting ways in which wave functions can acquire nonintegrable phase (commonly termed Berry’s phase, geometric phase, or topological phase) upon transport along paths in the parameter space. We emphasize the case of arbitrary paths on the Born–Oppenheimer potential energy surfaces (the parameter space of the electronic states in an isolated molecule) of the linear plus quadratic E⊗e Jahn–Teller system. It is found that these surfaces are degenerate not only at the origin but also at three other, equivalent points, which lie on a radius ρ=2k/g. Here k and g are the linear and quadratic vibronic coupling constants, respectively. This radius is then shown to mark a sharp transition between Jahn–Teller behavior, characterized by half‐odd‐integral vibronic angular momentum, and Renner–Teller behavior, which has integral angular momentum. Finally, we examine the conditions necessary for adiabatic evolution in the E⊗e system, and the observable consequences of the geometric phase.

Ionization-detected UV multiphoton absorption spectroscopy of the excited states of N2O is presented, showing Rydberg structure within 20,000/cm of the first ionization threshold. Despite evidence for strong Rydberg-continuum coupling in the form of broadened bands and Fano line-shapes, the Rydberg structure persists, with atomic-like quantum defects and vibration structure well-matched with that of the ion. In the most clearly resolved spectrum, corresponding to the 3p(delta)1Pi state, Renner-Teller and Herzberg-Teller coupling of electronic and vibrational angular momentum are revealed. It is suggested that these mixings are properties of the N2O(+)Pi ion core.

The two‐photon absorption spectra of the 3sE’ states of cyclopropane‐h6 and cyclopropane‐d6 are obtained by two‐photon resonant three‐photon ionization spectroscopy. Bands are vibronically resolved by virtue of a free‐jet expansion. The hot bands of these spectra suggest that the excited state is distorted in both the carbon ring deformation coordinate and the CH2 wag coordinate. These are the lowest e’ modes, and thus their activity can be interpreted as arising from Jahn–Teller interactions. A satisfactory fit of both line positions and intensities is achieved within this model. The dynamics and structure predicted by the Hamiltonian used are described. It is concluded that, in the ground vibronic state, nonadiabatic interactions are small, but the electronically excited molecule is nevertheless very fluxional, sampling a wide range of geometries. Morever, while only minimal barriers to pseudorotation exist in each coordinate individually, there is some locking of the phases of the two modes, so the pse...

The dynamics of infrared multiphoton excitation and dissociation of SF6 has been investigated under collision‐free conditions by a crossed laser–molecular beam method. In order to understand the excitation mechanism and to elucidate the requirements of laser intensity and energy fluence, a series of experiments have been carried out to measure the dissociation yield dependences on energy fluence, vibrational temperature of SF6, the pulse duration of the CO2 laser, and the frequency in both one and two laser experiments. Translational energy distributions of the primary dissociation product SF5, measured by time‐of‐flight and angular distributions and the dissociation lifetime of excited SF6 as inferred from the observation of secondary dissociation of SF5 into SF4 and F during the laser pulse suggest that the dynamics of dissociation of excited molecules is dominated by complete energy randomization and rapid intramolecular energy transfer and can be adequately described by RRKM theory. An improved phenom...

Optical-optical double resonance is employed to achieve state-to-state resolution in two-photon photodissociation. NO/sub 2/ seeded in a free-jet expansion is dissociated by sequential two-photon absorption in the region of 488 nm, just above the threshold for production of O(/sup 1/D). The channel to produce excited oxygen is observed to dominate the formation of vibrationally cold NO(X /sup 2/PI, nu = 0), which is detected by resonant two-photon ionization. For two-photon photolysis energies within 100 cm/sup 1 -/ of threshold, photodissociation dynamics, manifested in NO rotational and ..lambda..-doublet state distributions, are observed to be a sensitive function of parent intermediate state. NO populations are an oscillatory function of J, with varying patterns of ..lambda..-doublet preference that change with selected NO/sub 2/ intermediate state. Certain features in the photodissociation spectrum of NO/sub 2/ in this region are seen to correlate with product NO state total parity. At energies higher above threshold (> 200 cm/sup -1/), the oscillatory behavior in J is less pronounced and, accordingly, less sensitive to total photolysis energy. In this region a uniform ..lambda..-doublet preference also emerges.

The immediate impact of Webster v. Reproductive Health Services on the majority of abortions performed in the United States will be marginal. Even if most states enact provisions similar to those approved in Webster, no abortions would be outlawed, and only abortions performed after viability or performed in public hospitals would be directly affected. At one point, Webster had the potential for breaking new constitutional ground on the extent to which states may restrict counseling for abortion in state facilities, and by state employees. However, due to Missouri's failure to appeal the invalidation of some of these provisions, and to the limiting construction given to the provisions that were appealed, these issues were not fully joined before the Supreme Court. Their resolution is postponed to another day.