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Luminescence response of solids excited by surface recombination of atoms and dependence on atomic density
Neutral atomic beam used to measure total ionization cross section of argon atoms incident on low density argon gas
MHD power generator in which ionization of alkali atoms occurs by collision with excited noble gas atoms, calculating velocity-dependent cross section
In this contribution, we report on recent progress in coupled-cluster simulations of open-shell atomic nuclei using interactions consistently derived from chiral effective field theory. In particular, we compare different coupled-cluster approaches by computing binding energies and electric dipole polarizabilities in medium-mass calcium isotopes.
To accurately describe the energetics of transition metal systems, density functional approximations (DFAs) must provide a balanced description of s- and d- electrons. One measure of this is the sd transfer error, which has previously been defined as E ( 3 d n − 1 4 s 1 ) − E ( 3 d n − 2 4 s 2 ) . Theoretical concerns have been raised about this definition due to its evaluation of excited-state energies using ground-state DFAs. A more serious concern appears to be strong correlation in the 4s 2 configuration. Here, we define a ground-state measure of the sd energy imbalance, based on the errors of s- and d-electron second ionization energies of the 3d atoms, that effectively circumvents the aforementioned problems. We find an improved performance as we move from the local spin density approximation (LSDA) to the Perdew-Burke-Ernzerhof (PBE) generalized gradient approximation (GGA) to the regularized and restored Strongly Constrained and Appropriately Normed (r 2 SCAN) meta-GGA for first-row transition metal atoms. However, we find large (∼2 eV) ground-state sd energy imbalances when applying a Perdew–Zunger 1981 self-interaction correction. This is attributed to an “energy penalty” associated with the noded 3d orbitals. A local scaling of the self-interaction correction to LSDA results in a balance of s- and d-errors.
Producing enantioenriched molecules from racemic mixtures is essential for manufacturing. Traditional methods such as resolution, deracemization and enantioconvergent catalysis primarily involve separating or converting enantiomers without altering their structures, or functionalization of stereocentres at or proximal to functional groups. However, there are challenges in enantioselectively forging C–H bonds that are remote from functional groups via hydrogen atom transfer (HAT) with these methods. Here we introduce a strategy for the photoenzymatic stereoablative enantioconvergence of γ-chiral oximes using repurposed flavin-dependent ene-reductases. A photoinduced single-electron reduction of the γ-chiral oxime by an ene-reductase generates an iminyl radical, which then undergoes stereoablative 1,5-HAT at the γ-stereocentre. Subsequent chiral reconstruction through enzymatic HAT and spontaneous imine hydrolysis yields the γ-chiral ketone with high enantioselectivity. This work provides a robust method for remote stereoablative enantioconvergent HAT and broadens the synthetic utility of photobiocatalysis.
Local atomic arrangements and effects of cold working on degree of short-range order in nickel-10 atomic percent tungsten alloy
Cross sections for excitation of fine structure levels in neutral atomic oxygen and carbon by collision with hydrogen atoms
Atom-atom collision theory, comparing velocity criterion for inelastic scattering, Massey parameter and Landau-Zener parameter
Calculation of ionization cross section for atom to atom collisions and ion and electron recombination in dense neutral gases
Born approximation for ionization cross sections of H-atom H-atom collision with ground state and excited state factors
Forward scattering of metastable and ground state argon atoms after argon ion-atom charge transferring collisions, discussing excitation resonances
Atom-atom collisional excitation cross sections obtained from ionization cross sections, noting Thomson classical theory
Metastable atom detection system for ground state atom beams, measuring Ar beam density five orders lower than background gas density
Time dependent matrix elements for multistate impact-parameter calculations for atom-atom inelastic cross sections
Atomic H electron transition induced by H atom collisional-excitation rates at various thermal energies, explaining anomalous recombination lines in H 1 regions
Ionization cross sections for excited H atom- ground state H atom collisions, using Born approximation
Frequency shifts due to collisions between hydrogen atoms in an atomic hydrogen maser frequency standard are studied. Investigations of frequency shifts proportional to the spin exchange frequency shift cross section and those proportional to the duration of exchange collisions are discussed. The feasibility of operating a hydrogen frequency standard at liquid helium temperatures is examined.