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

In this report, we summarize and describe the recent unique updates and additions to the Molcas quantum chemistry program suite as contained in release version 8. These updates include natural and spin orbitals for studies of magnetic properties, local and linear scaling methods for the Douglas-Kroll-Hess transformation, the generalized active space concept in MCSCF methods, a combination of multiconfigurational wave functions with density functional theory in the MC-PDFT method, additional methods for computation of magnetic properties, methods for diabatization, analytical gradients of state average complete active space SCF in association with density fitting, methods for constrained fragment optimization, large-scale parallel multireference configuration interaction including analytic gradients via the interface to the Columbus package, and approximations of the CASPT2 method to be used for computations of large systems. In addition, the report includes the description of a computational machinery for nonlinear optical spectroscopy through an interface to the QM/MM package Cobramm. Further, a module to run molecular dynamics simulations is added, two surface hopping algorithms are included to enable nonadiabatic calculations, and the DQ method for diabatization is added. Finally, we report on the subject of improvements with respects to alternative file options and parallelization.

https://hal-amu.archives-ouvertes.fr/hal-01409053/document

Molcas 8: New capabilities for multiconfigurational quantum chemical calculations across the periodic table.

A numerical simulation study of the thermospheric winds produced by auroral heating during magnetic storms, and of their global dynamo effects, establishes the main features of the ionospheric disturbance dynamo. Driven by auroral heating, a Hadley cell is created with equatorward winds blowing above about 120 km at mid-latitudes. The transport of angular momentum by these winds produces a subrotation of the mid-latitude thermosphere or westward motion with respect to the earth. The westward winds in turn drive equatorward Pedersen currents which accumulate charge toward the equator, resulting in the generation of a poleward electric field, a westward E × B drift, and an eastward current. When realistic local time conductivity variations are simulated, the eastward mid-latitude current is found to close partly via lower latitudes, resulting in an ‘anti-Sq’ type of current vortex. Both electric field and current at low latitudes thus vary in opposition to their normal quiet-day behavior. This total pattern of disturbance winds, electric fields, and currents is superimposed upon the background quiet-day pattern. When the neutral winds are artificially confined on the nightside, the basic pattern of predominantly westward E × B plasma drifts still prevails on the nightside but no longer extends into the dayside. Considerable observational evidence exists, suggesting that the ionospheric disturbance dynamo has an appreciable influence on storm-time ionospheric electric fields at middle and low latitudes.

The ionospheric disturbance dynamo

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

A benchmark set of 28 medium-sized organic molecules is assembled that covers the most important classes of chromophores including polyenes and other unsaturated aliphatic compounds, aromatic hydrocarbons, heterocycles, carbonyl compounds, and nucleobases. Vertical excitation energies and one-electron properties are computed for the valence excited states of these molecules using both multiconfigurational second-order perturbation theory, CASPT2, and a hierarchy of coupled cluster methods, CC2, CCSD, and CC3. The calculations are done at identical geometries (MP26-31G*) and with the same basis set (TZVP). In most cases, the CC3 results are very close to the CASPT2 results, whereas there are larger deviations with CC2 and CCSD, especially in singlet excited states that are not dominated by single excitations. Statistical evaluations of the calculated vertical excitation energies for 223 states are presented and discussed in order to assess the relative merits of the applied methods. CC2 reproduces the CC3 reference data for the singlets better than CCSD. On the basis of the current computational results and an extensive survey of the literature, we propose best estimates for the energies of 104 singlet and 63 triplet excited states.

https://www.chemie.hhu.de/fileadmin/redaktion/Fakultaeten/Mathematisch-Naturwissenschaftliche_Fakultaet/Chemie/SFB_663/Veroeffentlichungen/C4_043.pdf

Benchmarks for electronically excited states: CASPT2, CC2, CCSD, and CC3

Most of our knowledge of the electronic structure of atoms and molecules is derived from excitation energies and transition probabilities. These observable quantities are related to the electronic wave functions by integrals over unmeasured variables. Another observable more directly related to the wave function than energy or transition probability is the single-electron momentum density, the probability that an electron in a well-defined orbital has a given value of momentum. Over the last twenty years a technique has been developed for measuring momentum densities in atoms and molecules. The technique, ([ital e],2[ital e]) spectroscopy, is based on electron-impact ionization with complete determination of the momenta of both incoming and outgoing electrons. The conditions necessary to extract momentum-density information from the ionization experiments are examined and related to general theories of electron scattering. Different experimental arrangements are reviewed and momentum-density results from selected examples are discussed.

(e,2e) spectroscopy

The six lowest excited states of benzene have been investigated in the gas‐phase free molecule at low pressure by electron‐impact spectroscopy. Incident electron energies of 13.6 and 20.0 eV and scattering angles from 9° to 80° were used. Three singlet–singlet transitions at 5.0, 6.2, and 6.9 eV were identified. These transitions agree with the results of optical absorption and higher‐energy electron‐impact experiments. In addition, three triplet states were observed at 3.9, 4.7, and 5.6 eV. The positions of the first two triplet states agreed with optical data on solid benzene and threshold electron‐impact experiments. The third triplet state at 5.6 eV was assigned on the basis of the relative intensity of the transition at various scattering angles. The ratio of the intensity of this transition to the allowed singlet–singlet transition at 6.9 eV was in a constant proportion to the corresponding ratio for the first triplet state (3.9 eV) at all scattering angles. The spacings of the first and second and second and third triplet states in benzene were determined to be 0.80 and 0.85 eV. The difference in the spacing is not significant with respect to experimental error.

Low‐Energy Electron‐Impact Study of the First, Second, and Third Triplet States of Benzene

Measurements of the ambient photoelectron spectrum from atmosphere explorer: II. AE-E measurements from 300 to 1000 km during solar minimum conditions

In this electron energy loss investigation of the electronic states of trans‐1,3‐butadiene, high energy resolution (25 meV) and a wide range of incident energies (9.5 to 49 eV) have been employed to locate and assign valence and Rydberg transitions in the typically congested 5–9 eV (2500 to 1400 A) region of the spectrum of a polyatomic molecule. Comparisons of the observed relative differential scattering cross sections (DCS) of various features in the lower energy (5.0 to 6.8 eV) region with the unambiguous assignments of these features from optical absorption and multiphoton ionization spectra allowed certain conclusions to be drawn regarding the typical DCS of Rydberg and valence singlet–singlet transitions. These ’’rules’’ have been applied to the congested 7–9 eV energy loss region of the butadiene spectrum. A diffuse process near 7.3 eV has been assigned as a forbidden valence transition, probably 1Ag←1Ag, on the basis of its relative DCS. The identification of the 7.07 and 8.00 eV transitions as successive members of the same Rydberg series is supported, and both transitions are demonstrated to contain considerable valence component.

Electron impact study of the energy levels of trans‐1,3‐butadiene: II. Detailed analysis of valence and Rydberg transitions

The daytime photoelectron energy spectrum has been measured at altitudes above 154 km by the photoelectron-spectrometer experiment on the Atmosphere Explorer-E satellite. Below 200 km, well-resolved peaks are observed in the spectrum corresponding to production of O(+) and N2(+) in various electronic states from photoionization of N2 and O by solar He II (304A) radiation. Vibration-rotation excitation of N2 by inelastic electron scattering is observed at 2.5 eV. The features due to nitrogen disappear from the spectrum at altitudes above 200 km.

John P. Doering

Papers

(e,2e) spectroscopy

Low‐Energy Electron‐Impact Study of the First, Second, and Third Triplet States of Benzene

Measurements of the ambient photoelectron spectrum from atmosphere explorer: II. AE-E measurements from 300 to 1000 km during solar minimum conditions

Electron impact study of the energy levels of trans‐1,3‐butadiene: II. Detailed analysis of valence and Rydberg transitions

High resolution daytime photoelectron energy spectra from AE-E