There is, I think, something ethereal about i —the square root of minus one. I remember first hearing about it at school. It seemed an odd beast at that time—an intruder hovering on the edge of reality.

Usually familiarity dulls this sense of the bizarre, but in the case of i it was the reverse: over the years the sense of its surreal nature intensified. It seemed that it was impossible to write mathematics that described the real world in …

I and i

Annals of physics

Recoil-ion and electron momentum spectroscopy is a rapidly developing technique that allows one to measure the vector momenta of several ions and electrons resulting from atomic or molecular fragmentation. In a unique combination, large solid angles close to 4π and superior momentum resolutions around a few per cent of an atomic unit (a.u.) are typically reached in state-of-the art machines, so-called reaction-microscopes. Evolving from recoil-ion and cold target recoil-ion momentum spectroscopy (COLTRIMS), reaction-microscopes—the `bubble chambers of atomic physics'—mark the decisive step forward to investigate many-particle quantum-dynamics occurring when atomic and molecular systems or even surfaces and solids are exposed to time-dependent external electromagnetic fields. This paper concentrates on just these latest technical developments and on at least four new classes of fragmentation experiments that have emerged within about the last five years. First, multi-dimensional images in momentum space brought unprecedented information on the dynamics of single-photon induced fragmentation of fixed-in-space molecules and on their structure. Second, a break-through in the investigation of high-intensity short-pulse laser induced fragmentation of atoms and molecules has been achieved by using reaction-microscopes. Third, for electron and ion-impact, the investigation of two-electron reactions has matured to a state such that the first fully differential cross sections (FDCSs) are reported. Fourth, comprehensive sets of FDCSs for single ionization of atoms by ion-impact, the most basic atomic fragmentation reaction, brought new insight, a couple of surprises and unexpected challenges to theory at keV to GeV collision energies. In addition, a brief summary on the kinematics is provided at the beginning. Finally, the rich future potential of the method is briefly envisaged.

/pdf/recoil-ion-and-electron-momentum-spectroscopy-reaction-c7ai542e3l.pdf

Recoil-ion and electron momentum spectroscopy: reaction-microscopes

▪ Abstract Turbulence affects the structure and motions of nearly all temperature and density regimes in the interstellar gas. This two-part review summarizes the observations, theory, and simulations of interstellar turbulence and their implications for many fields of astrophysics. The first part begins with diagnostics for turbulence that have been applied to the cool interstellar medium and highlights their main results. The energy sources for interstellar turbulence are then summarized along with numerical estimates for their power input. Supernovae and superbubbles dominate the total power, but many other sources spanning a large range of scales, from swing-amplified gravitational instabilities to cosmic ray streaming, all contribute in some way. Turbulence theory is considered in detail, including the basic fluid equations, solenoidal and compressible modes, global inviscid quadratic invariants, scaling arguments for the power spectrum, phenomenological models for the scaling of higher-order structu...

http://www.ifa.hawaii.edu/%7Ereipurth/reviews/elmegreen1_araa.pdf

Interstellar Turbulence I: Observations and Processes

Cold Target Recoil Ion Momentum Spectroscopy: a &momentum microscope' to view atomic collision dynamics

sections D. V. Fursa1, L. H. Scarlett1, J. K. Tapley1, J. S. Savage1, M. C. Zammit2, I. Bray1, M. Zawadzki3, R. Wright4, G. Dolmat4, M. F. Martin4, L. Hargreaves4, M. A. Khakoo4 1 Curtin Institute for Computation, Curtin University, Perth, Western Australia 6102, Australia 2 Theoretical Division, Los Alamos National Laboratory, Los Alamos, New Mexico, USA 3 Department of Physics, Gdansk University of Technology, Gdansk, Poland 4 Department of Physics, California State University, Fullerton, USA

Electron-impact dissociation of molecular hydrogen: Benchmark cross sections

Photoionization, Rayleigh, and Raman scattering cross sections for the alkali atoms

Angular correlation parameters. A, R, the circular polarization parameter/and the differential cross section are measured for the electron impact excitation of hydrogen atoms to the 32Pj states at an incident electron energy of 54.42 eV and for electron scattering angles up to 35°. Comparison of the measurements with the convergent close-coupling calculations of Bray and Stelbovics shows excellent agreement with experiment.

Angular and polarization correlation measurements for the 32P states of atomic hydrogen

Basic features of a new surface-integral formulation of scattering theory are outlined. This formulation is valid for both short-range and Coulombic longe-range interactions. New general definitions for the potential scattering amplitude are given. For the Coulombic potentials the generalized amplitude gives the physical on-shell amplitude without recourse to a renormalization procedure. New post and prior forms for the amplitudes of breakup, direct and rearrangement scattering in a Coulomb three-body system are presented.

https://iopscience.iop.org/article/10.1088/1742-6596/194/1/012017/pdf

Scattering theory with the Coulomb potential

The response of an atom to the action of a pulse shorter than the Kepler period of the optically-active electron is often treated analytically using the sudden-perturbation approximation (SPA). It relies on the truncation of the evolution operator expansion in a series over the dimensionless parameter e
 sys
 τ
 L, where e
 sys is the system-dependent characteristic energy and τ
 L is the pulse duration. We examine the SPA with the use of a basis-based solution of the time-dependent Schrodinger equation (TDSE) for the case of a hydrogen atom interacting with two different types of ultrashort pulses, a half-cycle pulse and a few-cycle pulse. The length-gauge form of the electron-field interaction potential is used. The SPA transition probabilities are shown to deviate slightly but systematically from the correct values for the positive-energy states in the region where the sudden-perturbation condition is violated. It is shown that the SPA expectation value of the electron displacement as a function of time differ qualitatively from what follows from the ab initio TDSE solution. Nevertheless, the SPA is shown to be a good approximation for the description of the expectation value of the electron momentum.

Igor Bray

Papers

Electron-impact dissociation of molecular hydrogen: Benchmark cross sections

Photoionization, Rayleigh, and Raman scattering cross sections for the alkali atoms

Angular and polarization correlation measurements for the 32P states of atomic hydrogen

Scattering theory with the Coulomb potential

Sudden perturbation approximations for interaction of atoms with intense ultrashort electromagnetic pulses