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Using electrospray ion beam deposition, we collide the complex molecule Reichardt's dye (C_{41}H_{30}NO^{+}) at low, hyperthermal translational energy (2-50 eV) with a Cu(100) surface and image the outcome at single-molecule level by scanning tunneling microscopy. We observe bond-selective reaction induced by the translational kinetic energy. The collision impulse compresses the molecule and bends specific bonds, prompting them to react selectively. This dynamics drives the system to seek thermally inaccessible reactive pathways, since the compression timescale (subpicosecond) is much shorter than the thermalization timescale (nanosecond), thereby yielding reaction products that are unobtainable thermally.

Rayleigh-Taylor instability growth is shown to be hydrodynamically scale invariant in convergent cylindrical implosions for targets that varied in radial dimension and implosion timescale by a factor of 3. The targets were driven directly by laser irradiation providing a short impulse, and instability growth at an embedded aluminum interface occurs as it converges radially inward by a factor of 2.25 and decelerates on a central foam core. Late-time growth factors of 14 are observed for a single-mode m=20 azimuthal perturbation at both scales, despite the differences in laser drive conditions between the experimental facilities, consistent with predictions from radiation-hydrodynamics simulations. This platform enables detailed investigations into the limits of hydrodynamic scaling in high-energy-density systems.

Exclusive cross sections and momentum distributions have been measured for quasifree one-neutron knockout reactions from a ^{54}Ca beam striking on a liquid hydrogen target at ∼200 MeV/u. A significantly larger cross section to the p_{3/2} state compared to the f_{5/2} state observed in the excitation of ^{53}Ca provides direct evidence for the nature of the N=34 shell closure. This finding corroborates the arising of a new shell closure in neutron-rich calcium isotopes. The distorted-wave impulse approximation reaction formalism with shell model calculations using the effective GXPF1Bs interaction and ab initio calculations concur our experimental findings. Obtained transverse and parallel momentum distributions demonstrate the sensitivity of quasifree one-neutron knockout in inverse kinematics on a thick liquid hydrogen target with the reaction vertex reconstructed to final state spin-parity assignments.

The process of a positron $\unicode{x2013}$ bound-electron annihilation with simultaneous emission of two photons is investigated theoretically. A fully relativistic formalism based on $\textit{ab initio}$ QED description of the process is worked out. The developed approach is applied to evaluate the annihilation of a positron with $K$-shell electrons of a silver atom, for which a strong contradiction between theory and experiment was previously stated. The results obtained here resolve this long-standing disagreement and, moreover, demonstrate a sizeable difference with approaches so far used for calculations of the positron $\unicode{x2013}$ bound-electron annihilation process, namely, the $\textit{Lee's}$ and $\textit{impulse}$ approximations., 11 pages, 4 figures, 1 table, 46 references

The isospin character of p-n pairs at large relative momentum has been observed for the first time in the ^{16}O ground state. A strong population of the J,T=1,0 state and a very weak population of the J,T=0,1 state were observed in the neutron pickup domain of ^{16}O(p,pd) at 392 MeV. This strong isospin dependence at large momentum transfer is not reproduced by the distorted-wave impulse approximation calculations with known spectroscopic amplitudes. The results indicate the presence of high-momentum protons and neutrons induced by the tensor interactions in the ground state of ^{16}O.

We show in a simple exactly solvable toy model that a properly designed impulse perturbation can transiently cool down low-energy degrees of freedom at the expense of high-energy ones that heat up. The model consists of two infinite-range quantum Ising models: one, the high-energy sector, with a transverse field much bigger than the other, the low-energy sector. The finite-duration perturbation is a spin exchange that couples the two Ising models with an oscillating coupling strength. We find a cooling of the low-energy sector that is optimized by the oscillation frequency in resonance with the spin exchange excitation. After the perturbation is turned off, the Ising model with a low transverse field can even develop a spontaneous symmetry breaking despite being initially above the critical temperature.

An experimental determination of the single-particle mean kinetic energies for 3He along the T = 2.00 K isotherm in the dense liquid and in the solid hcp and bcc phases is reported. Deep-inelastic neutron scattering measurements at exchanged wave vectors ranging from 90.0 to 140.0 A(-1) have been performed in order to evaluate, within the framework of the impulse approximation, the molar volume dependence of the kinetic energy. The results are found in excellent agreement with recent diffusion Monte Carlo simulations.

Stable numerical convolution of the diffusion impulse time response with a Gaussian wave packet produces a wave packet whose delay time is governed by an eikonal equation where the diffusivity distribution plays the role of the square of the velocity distribution. Diffusion delay time tomography data can approximately image the diffusivity distribution by solving an inverse problem for the eikonal equation with multiple rays that traverse low diffusivity regions not traversed by earlier related methods, and consequently the resolution in such regions is improved. This is important for medical imaging.

The quantal impulse cross section is derived in a novel form appropriate for direct classical correspondence. The classical impulse cross section is then uniquely defined and yields the first general classical expression for nl-n(')l(') collisional transitions. The derived cross sections satisfy the optical theorem and detailed balance. Direct connection with the classical binary encounter approximation is also firmly established. The unified method introduced is general in its application to various collision and recombination processes and enables new directions of enquiry to be pursued quite succinctly.

The behavior of the nuclear matter response in the region of large momentum transfer, in which plane wave impulse approximation predicts the onset of y-scaling, is discussed. The theoretical analysis shows that scaling violations produced by final state interactions are driven by the momentum dependence of the nucleon-nucleon scattering cross section. Their study may provide valuable information on possible modifications of nucleon-nucleon scattering in the nuclear medium., 4 pages with 3 figures. To appear in Physical Review Letters

There exist substantial discrepancies between theoretical predictions for the cross section of double ionization in helium by Compton scattering. Consistency between different approaches has been reached for the high-energy asymptotic value of the double-to-single ionization ratio RC s 21 C s 1 C (cf. [1], and references therein), but the available theoretical results differ strongly in their predictions for the energy dependence of RC leading up to this limit. The sparsity and large uncertainty of published experimental results have previously prohibited a conclusive assessment of any of these predictions. The main impediment to experimental determinations of RC arises from the smallness of the Compton cross section of about 10 224 cm 2 . The fundamental difficulty for theoretical treatments lies in accounting adequately for electron correlation in the initial bound and final continuum states of the system. Part of this difficulty is circumvented in the impulse approximation (IA), where only a correlated initial-state wave function is needed in the calculation. At energies as low as 6 keV the x-ray inelastic scatter

We show that, in second-order phase transformations induced by an inhomogeneous quench, the density of topological defects is drastically suppressed as the velocity with which the quench propagates becomes smaller than the speed at which the front of the broken symmetry phase spreads. The velocity of the broken symmetry phase front is approximately given by the ratio of the healing length to relaxation time at freeze-out, that is at the instant when the critical slowing down results in a transition from the adiabatic to the impulse behavior in the order parameter. Experimental implications are briefly discussed., Comment: 5 pages, Latex, 2 figures, final version with minor changes

The signal generated by a weak impulse propagates in an oscillatory way and dispersively in a gravitationally compacted granular chain. For the power-law type contact force, we show analytically that the type of dispersion follows power-laws in depth. The power-law for grain displacement signal is given by $h^{-1/4(1-1/p)}$ where $h$ and $p$ denote depth and the exponent of contact force, and the power-law for the grain velocity is $h^{-1/4({1/3}+1/p)}$. Other depth-dependent power-laws for oscillation frequency, wavelength, and period are given by combining above two and the phase velocity power-law $h^{1/2(1-1/p)}$. We verify above power-laws by comparing with the data obtained by numerical simulations., Comment: 12 pages, 3 figures; Changed content

A simple analytic formula is derived for the impulse that will produce approximately, for arbitrarily large population transfer, a specified wave packet in a Rydberg atom. This solution to the nonlinear control problem is obtained in the limit that the duration of the pulsed control field is less than the Kepler period of the system. The validity of our solution is tested by comparison with a direct numerical integration of Schr\"odinger's equation, and it is found to yield the target state and population transfer with very high fidelity.

The (e,e'p) reaction was studies on targets of C, Fe, and Au at momentum transfers squared Q{sup 2} of 0.6, 1.3, 1.8 and 3.3 GeV{sup 2} in a region of kinematics dominated by quasifree electron-proton scattering. Missing energy and missing momentum distributions are reasonably well described by plane wave impulse approximation calculations with Q{sup 2} and A dependent corrections that measure the attenuation of the final state protons.

The cross section of the He-4(e, e'p)H-3 reaction has been measured for missing momenta 220 less than or equal to p(m) less than or equal to 690 MeV/c to study high-momentum components of the nuclear wave function and the reaction mechanism for this transition. The zero predicted in the plane-wave impulse approximation (PWIA) cross section, due to the underlying pt momentum distribution, is found to be washed out. Three types of calculations indicate that this is caused by final-state interactions and contributions from two-body currents. The calculations reproduce the high p(m) (600-690 MeV/c) data, although due to different ingredients in the models.

The surface-wave scattering processes responsible, in part, for the optical glory have never been compared with theoretical predictions. Here, THz impulse ranging is used to measure the time domain impulse response of spherical targets with sufficiently high temporal resolution to permit the surfacewave contribution to the total impulse response to be isolated. The first direct experimental comparison for the surface wave with Mie theory as well as the surface-wave approximation of van de Hulst is performed. Interference of the surface waves from a dielectric sphere is shown to lead to the frequency and angular intensity dependence of the THz glory. [S0031-9007(97)04970-3] PACS numbers: 42.25.Fx

The probability distribution of electronic excitations of HeT+ following the beta decay of the T-2 molecule has been calculated for the first time in the beyond sudden impulse approximation, removi ...

We have made a direct determination of the diffusion rates in a stored, coasting antiproton beam by observing the decay rates associated with beam echoes in the longitudinal plane. The beam echoes, similar to those observed in other fields of physics, are generated by a sequential impulse excitation at harmonics of the beam revolution frequency. The echo envelope follows a characteristic response which, however, can be modified by the presence of even a very weak scattering process, permitting a sensitive determination of the longitudinal diffusion rate in the beam. {copyright} {ital 1996 The American Physical Society.}

A breakdown of the Impulse Approximation is studied in pion photoproduction on $^3$He at high momentum transfers. The usual DWIA formalism with Faddeev wave functions which works well for small momentum transfers deviates from experimental measurements by up to two orders of magnitude for $Q^2>6 fm^{-2}$. It is found that the explicit inclusion of two-body mechanisms, where the photon is absorbed on one nucleon and the pion is emitted from another nucleon can restore agreement with the data., 10 pages, 3 figures (available as postscript files from the authors) Mainz preprint MKPH-T-94-13

Photoionization of two-electron systems is studied. The nonrelativistic impulse approximation is applied to treat the Compton ionization contributions. For asymptotically high energies this treatment formally reduces to the generalized shake theory and predicts a limit for the ratio of double to single ionization different from that for photoeffect. At finite energies the ratio for He, which includes both Compton and photoeffect contributions, is marginally in agreement with experimental results but it disagrees with previous theoretical calculations.

We measured with unprecedented precision the induced polarization P(y) in (4)He(e,e'p)(3)H at Q(2)=0.8 and 1.3 (GeV/c)(2). The induced polarization is indicative of reaction-mechanism effects beyond the impulse approximation. Our results are in agreement with a relativistic distorted-wave impulse approximation calculation but are overestimated by a calculation with strong charge-exchange effects. Our data are used to constrain the strength of the spin-independent charge-exchange term in the latter calculation.

A complete set of diagonal spin-transfer observables has been measured at excitation energies between 30 and 40 MeV for inelastic proton scattering from $^{40}\mathrm{Ca}$ at 497 and 581 MeV at a momentum transfer of 0.56 ${\mathrm{fm}}^{\mathrm{\ensuremath{-}}1}$. The longitudinal and transverse spin-flip probabilities are deduced. Their unequal enhancements relative to free nucleon-nucleon scattering values are explained by a distorted-wave impulse approximation calculation in which the finite nucleus random-phase approximation is used to describe the nuclear respose.

We have developed an exact second-order S-matrix code for the relativistic numerical calculation of cross sections for Compton scattering of photons by bound electrons within the independent-particle approximation. We find good agreement with less exact treatments in regions where such theories are valid, recovering the impulse approximation and the soft-photon infrared divergence. We do not find agreement with an earlier calculation of Whittingham. We compare with recent scattering experiments in the regime Z\ensuremath{\alpha}(\ensuremath{\Elzxh}${\mathrm{\ensuremath{\omega}}}_{\mathit{i}}$)\ensuremath{\sim}${\mathit{E}}_{\mathit{B}}$, where we find that the impulse approximation is not adequate.

A serious breakdown of the distorted-wave impulse approximation has recently been observed in the proton-knockout reaction $^{4}\mathrm{He}$(e,e'p${)}^{3}$H. In the phenomenological description of the data, charge-excnange contributions were included through a coupled-channel calculation. New data obtained in a wide range of kinematical configurations are presented in order to study the anomaly in more detail. Its magnitude and dependence on momentum transfer are well accounted for by a newly presented microscopic description of various interaction effects, including meson-exchange currents and charge-exchange processes.

We present a measurement of the spin-dependent cross sections for the \vec{^3He}(\vec{e},e')X} reaction in the quasielastic and resonance regions at four-momentum transfer 0.1 < Q^2< 0.9 GeV^2. The spin-structure functions have been extracted and used to evaluate the nuclear Burkhardt--Cottingham and extended GDH sum rules for the first time. Impulse approximation and exact three-body Faddeev calculations are also compared to the data in the quasielastic region., Final version

The ratio of transverse and longitudinal response functions is investigated for the quasielastic reaction {sup 6}Li({ital e},{ital e}{prime}{ital p}). The ratio itself and its dependence on the missing energy cannot be explained in the distorted-wave impulse approximation. It is proposed that a reaction mechanism other than quasielastic one-body knockout plays a significant role.

We have measured the continuum momentum distribution for radiative electron capture to the continuum (RECC) cusp electrons in 90A MeV U{sup 88+}+N{sub 2}{yields}U{sup 88+}+(N{sub 2}{sup +}*)+e{sub cusp}(0 deg.)+h{nu} (RECC) collisions. We demonstrate that x rays coincident with RECC cusp electrons originate from the short-wavelength limit of the electron-nucleus bremsstrahlung and explain the asymmetric cusp shape by comparison with theory within the relativistic impulse approximation.

We provide integrated cross sections for quasielastic charged-current neutrino-nucleus scattering. Results evaluated using the phenomenological scaling function extracted from the analysis of experimental $(e,e')$ data are compared with those obtained within the framework of the relativistic impulse approximation. We show that very reasonable agreement is reached when a description of final-state interactions based on the relativistic mean field is included. This is consistent with previous studies of differential cross sections which are in accord with the universality property of the superscaling function., 5 pages, 3 figures, to be published in Phys. Rev. Lett

We show that a small crystal trapped within a potential well and in contact with its own fluid, responds to large compressive stresses by a novel mechanism -- the transfer of complete lattice layers across the solid-fluid interface. Further, when the solid is impacted by a momentum impulse set up in the fluid, a coherently ejected lattice layer carries away a definite quantity of energy and momentum, resulting in a sharp peak in the calculated phonon absorption spectrum. Apart from its relevance to studies of stability and failure of small sized solids, such coherent nanospallation may be used to make atomic wires or monolayer films., Comment: 4 pages, 4 figures, published version, changed content

The R\"ontgen quantum phase shift is exhibited by the interference of point particles endowed with an electric dipole moment due to their motion relative to a source of the magnetic field. Here we show, using arguments involving the classical concepts of force and its impulse, that the R\"ontgen phase shift arises within a largely classical (semiclassical) theoretical framework. All the subtleties normally associated with the nonlocality of magnetic (Aharonov-Bohm-type) quantum phase phenomena are uncontroversially absent in the classical treatment.

New, high-precision measurements of the 3He(e,ep) reaction using the A1 Collaboration spectrometers at the Mainz microtron MAMI are presented. These were performed in antiparallel kinematics at energy transfers below the quasielastic peak, and at a central momentum transfer of 685 MeV/c. Cross sections and distorted momentum distributions were extracted and compared to theoretical predictions and existing data. The longitudinal and transverse behavior of the cross section was also studied. Sizable differences in the cross-section behavior from theoretical predictions based on the plane wave impulse approximation were observed in both the two- and three-body breakup channels. Full Faddeev-type calculations account for some of the observed excess cross-section, but significant differences remain. (Less)

Using a system consisting of a freely falling cloud of cold cesium atoms periodically kicked by pulses from a vertical standing wave of laser light, we present the first experimental observation of high-order quantum accelerator modes. This confirms the recent prediction by Fishman, Guarneri, and Rebuzzini [Phys. Rev. Lett. 89, 084101 (2002)]. We also show how these accelerator modes can be identified with the stable regions of phase space in a classical-like chaotic system, despite their intrinsically quantum origin., Comment: 4 pages, 3 figures, submitted to Phys. Rev. Lett

We have studied the (π - , K + ) reaction on a silicon target to investigate the sigma-nucleus potential. The inclusive spectrum was measured at a beam momentum of 1.2 GeV/c with an energy resolution of 3.3 MeV (FWHM) by employing the superconducting kaon spectrometer system. The spectrum was compared with theoretical calculations within the framework of the distorted-wave impulse approximation, which demonstrates that a strongly repulsive sigma-nucleus potential with a nonzero size of the imaginary part reproduces the observed spectrum.

Ultrashort, nearly unipolar electric field pulses are used to produce novel dynamic states in Rydberg atoms. A single 500 fsec field pulse redistributes essentially all of the population from a single stationary Rydberg state to hundreds of different final states. The dynamic evolution of the nonstationary wave packet is monitored using a second, time-delayed pulse. The time-dependent momentum-space probability distribution of the wave packet can be retrieved experimentally using a classical impulse approximation. {copyright} {ital 1996 The American Physical Society.}

This Letter reports the first measurements of the angular distribution of Auger electrons emitted from the decay of the (1s2s2${\mathit{p}}^{2}$${)}^{3}$D ${\mathrm{O}}^{4+\mathrm{*}\mathrm{*}}$ doubly excited state formed predominantly through resonant transfer and excitation (RTE) in collisions of 13-MeV ${\mathrm{O}}^{5+}$ projectiles with He. The (1s2s2${\mathit{p}}^{2}$${)}^{3}$D angular distribution is strongly peaked along the beam direction, in agreement with recent calculations of the RTE angle-dependent impulse approximation. Furthermore, interference effects between the RTE and the elastic target direct-ionization channels are observed.

Data are presented for the (/sup 3/He, t) reaction at energies of 600 MeV, 1.2 GeV, and 2 GeV on targets /sup nat/C, /sup 54/Fe, and /sup 89/Y. The low--excitation-energy regions of the spectra are dominated by isospin-spin excitations. Cross-section calculations in distorted-wave impulse approximation with parameters from NN data account reasonably well for the data. At 2-GeV bombarding energy a strong excitation of the ..delta.. resonance is observed for all targets.

Cross sections and T/sub 20/ analyzing powers for dA..-->..pX are presented. A shoulder in the cross section previously reported at higher energies and for carbon is observed for H, C, and Ti at the same d-c.m.-frame proton momentum q = 0.35 GeV/c. At q

On presente une nouvelle methode rapide, avec multiplexage de frequences, entierement optique de spectrometrie d'absorption d'ultrasons en phase gazeuse. Un laser a impulsions produit une impulsion acoustique de courte duree dans l'echantillon de gaz et les profils des impulsions acoustiques a 2 distances sont controles par des faisceaux sonde continus focalises

This Letter demonstrate importance of two reactions with high threshold-fission of nuclei around the lead region and high-multiplicity nucleon emission-in studying the high-energy tail of the nuclear response function in muon capture. Conventional impulse approaches and the recently proposed absorption model of the nonimpulse variety are shown to give significantly different yields for these reactions.

The total reaction cross sections for intermediate-energy proton scattering on /sup 40/Ca and /sup 208/Pb are calculated within the Dirac-eikonal formalism. Comparison with data indicates that the recently proposed impulse-approximation Dirac optical potential for nucleon-nucleus scattering is quite adequate, and accounts for 90% of the measured total reaction cross section.

In this application of Dirac phenomenology a relativistic impulse approximation is used to describe proton-nucleus elastic scattering at intermediate energies. The results demonstrate the superiority of this relativistic treatment over the nonrelativistic impulse approximation, especially with regard to spin observables. The method has important implications with respect to the extraction of neutron distributions.

The /sup 4/He( p,2p)/sup 3/H reaction has been measured at 250, 350, and 500 MeV using symmetric geometries. The energy dependence of the cross section at zero recoil momentum and angular distributions are presented. The data are compared to distorted-wave impulse-approximation (DWIA) calculations. Unlike at lower energies, the zero-recoil-momentum data are well described by the DWIA at these energies. For the angular distributions, the DWIA increasingly underestimates the data as the recoil momentum is increased.

Three recents Letters have presented Dirac-equation optical-model calculations for intermediate-energy nucleon-nucleus scattering based upon a relativistic impulse approximation. In these works the relativistic impulse approximation is shown to be capable of explaining certain features of the experimental data that resist all attempts at a nonrelativistic impulse-approximation description. The reasons for the success of these relativistic impulse-approximation calculations are analyzed in the present work.