Electron spectroscopy of doubly excited states in He produced by slow collisions of He2+ ions with Ba atoms

We measured ejected electron spectra caused by autoionization of doubly excited states in He atoms; the excited He was made by double electron capture of low-energy He2+ ions colliding with Ba atoms. Measurements were performed by means of zero degree electron spectroscopy at projectile energies from 40 to 20 keV. Electron spectra due to autoionization from the states He(2lnl') to He+(1s) for n greater than or equal to2, and those from He(3lnl') to He+ (2s or 2p) for n greater than or equal to3, were observed. Line peaks in the spectra were identified by comparing observed electron spectra with those of several theoretical calculations. It was found that doubly excited states of relatively high angular momenta such as the D and F terms were conspicuously created in a quite different manner from the cases of the production of doubly excited states by the use of photon, electron, or ion impacts on neutral He atoms. Rydberg states with large n values were observed with high population in both the He(2lnl') and He(3lnl') series. Other remarkable features in the electron spectra are described and the mechanisms for the production of these electron spectra are discussed qualitatively.

Hydrogen abstraction from ionic liquids by benzophenone triplet excited states

The activation energy for hydrogen abstraction from imidazolium-based ionic liquids is significantly higher than that observed in conventional solvents.

Mixing of dielectronic and multiply-excited states in electron-ion recombination: a study of Au24+

It has been suggested (Gribakin et al 1999 Aust. J. Phys. 52 443–57, Flambaum et al 2002 Phys. Rev. A 66 012713) that strongly enhanced low-energy electron recombination observed in Au25+ (Hoffknecht et al 1998 J. Phys. B: At. Mol. Opt. Phys. 31 2415–28) is mediated by complex multiply excited states, while simple dielectronic excitations play the role of doorway states for the electron capture process. We present the results of an extensive study of con?guration mixing between doubly excited (doorway) states and multiply excited states which account for the large electron recombination rate on Au25+ . A detailed analysis of spectral statistics and statistics of eigenstate components shows that the dielectronic doorway states are virtually ‘dissolved’ in complicated chaotic multiply excited eigenstates. This work provides a justi?cation for the use of statistical theory to calculate the recombination rates of Au25+ and similar complex multiply charged ions. We also investigate approaches which allow one to study complex chaotic many-body eigenstates and criteria of strong con?guration mixing, without diagonalizing large Hamiltonian matrices.

The distorted-wave impulse approximation for electron capture into excited states

Total cross sections for electron capture are calculated for collisions of fast protons and a-particles with atomic hydrogen. The distorted-wave impulse approximation is applied over the energy range 10-1500 keV/u. State-selective results are given for the 1s, 2s and 2p levels. Both the post and prior forms of the model are calculated and compared with results from other theories and experimental measurements. In general the model performs very well in comparison with experiment over this energy range though discrepancies arise at lower energies.

CONTRIBUTION OF RESONANCE RAMAN EXCITATION SPECTROSCOPY FOR PROBING ELECTRONICALLY EXCITED-STATES - NATURE OF A PORPHYRIN-DNA EXCIPLEX

The resonance Raman spectra of a water-soluble metalloporphyrin Cu(TMpy-P4), complexed with a synthetic nucleic acid, poly(dA-dT), were measured by using excitation wavelengths located within the B (Soret) transition of the porphyrin (417-470 nm), while its excited state was synchronously pumped with 545-nm pulsed excitation corresponding to the Q transition. In the presence of pump pulses, the aqueous solution of the Cu(TMpy-P4).poly(dA-dT) complex exhibits resonance Raman bands at 1558 and 1353 cm-1 that are not observed in the absence of pump pulses. These new features were previously assigned to electronically excited Cu(TMpy-P4), stabilized by forming an exciplex with the A-T sites of the nucleic acid. Here we present resonance Raman excitation profiles (RREP) of both the excited and ground states of the complex, and we experimentally confirm the very short lifetime of the exciplex. To our knowledge this is the first time that a RREP of a very short lived (ca. 20 ps) intermediate excited state has been obtained with a two-color experiment. We use this to help to characterize the nature of the porphyrin-AT specific complex formed in the porphyrin excited state.

Calculations for doubly-excited states populated in two-electron processes

Recent calculations of doubly-excited states for two and four-electron states in neutral atoms and ions are described. In particular the radiative properties of these states are considered. It is pointed out that some of these states live so long that triply-excited states perhaps can be formed in neutralisation processes at surfaces. © 1991 Springer-Verlag.

Electron-impact ionization of the metastable excited states of Li +

Electron-impact ionization cross sections for the 1s2s 1S and 1s2s 3S metastable states of Li+ are calculated using both perturbative distorted-wave and non-perturbative close-coupling methods. Term-resolved distorted-wave calculations are found to be approximately 15% above term-resolved R-matrix with pseudostates calculations. On the other hand, configuration-average time-dependent close-coupling calculations are found to be in excellent agreement with the configuration-average R-matrix with pseudostates calculations. The non-perturbative R-matrix and close-coupling calculations provide a benchmark for experimental studies of electron-impact ionization of metastable states along the He isoelectronic sequence.

The validity of classical trajectory and perturbative quantal methods for electron-impact ionization from excited states in H-like ions

To test the validity of classical trajectory and perturbative quantal methods for electron-impact ionization of H-like ions from excited states, we have performed advanced close-coupling calculations of ionization from excited states in H, Li 2+ and B 4+ using the R -matrix with pseudo states and the time-dependent close-coupling methods. Comparisons with our classical trajectory Monte Carlo (CTMC) and distorted-wave (DW) calculations show that the CTMC method is more accurate than the DW method for H, but does not improve with n and grows substantially worse with Z , while the DW method improves with Z and grows worse with n .

TRANSIENT RESONANCE RAMAN AND RAMAN SPECTROELECTROCHEMICAL STUDIES OF CUI COMPLEXES WITH POLYPYRIDYL LIGANDS

Studies by laser flash photolysis, transient Raman spectroscopy, and Raman and UV-vis spectroelectrochemistry are described in which the techniques have been used in parallel to compare the lowest energy charge-transfer excited states of Cu (1) complexes ([Cu(L)2]+ and [ (PPh3)2Cu(L)]+ [L = 2,2'-biquinoline (BIQ) or 6,7-dihydro-5,8-dimethyldibenzo[b,j] [1,10]-phenanthroline (DMCH)) with the species produced by electrochemical reduction in the same group of complexes. Transient resonance Raman spectra for the metal-to-ligand charge-transfer (MLCT) states of [Cu(DMCH)2]+ (1), [Cu(BIQ)2]+ (2), [Cu(DMCH)(PPh3)2]+ (3), and [Cu(BIQ)(PPh3)2]+ (4) are compared with the resonance Raman spectra of the same group of complexes following one-electron electrochemical reduction of the DMCH and BIQ ligands. The UV-vis and resonance Raman evidence suggests that the electrochemical reduction of the [Cu(I)L2]+ species proceeds according to the sequence [LCu(I)L]+ -->e- [LCu0L] -->e- [L.-Cu(I)L.-]-. Several features assignable to modes of the electrochemically generated DMCH.-and BIQ'- radical anions exhibit a close correspondence in both frequency and relative intensity with counterparts in the spectra of the MLCT states of 1 and 2. A notable exception is a band near 1590 cm-1 in the spectra of the electrochemically reduced species which occurs some 15 cm-1 lower in the corresponding spectra of the excited-state species. It is suggested that the shift may reflect the change in oxidation state of the metal center from Cu(I) to Cu(II) which occurs as a result of charge-transfer excitation.

TIME-RESOLVED ABSORPTION, INFRARED, AND RESONANCE RAMAN-SPECTRA OF THE COMPLEXES [RU(X)(R)(CO)(2)(ALPHA-DIIMINE)] (X=HALIDE R=ALKYL) - INFLUENCE OF X ON THE CHARGE-TRANSFER CHARACTER OF THE LOWEST EXCITED-STATE

Nanosecond time-resolved absorption (TA), resonance Raman (TR(3)), and infrared (TRIR) spectra are reported for several complexes [Ru(X)(R)(CO)(2)(alpha-diimine)] (X = Cl, Br, I; R = Me, Et; alpha-diimine = N,N'-diisopropyl-1,4-diaza-1,3-butadiene (iPr-DAB), pyridine-2-carbaldehyde-N-isopropylimine (iPr-PyCa), 2,2'-bipyridine (bpy)). This is the first instance in which the TA, TR(3), and TRIR techniques have been used to probe excited states in the same series of complexes. The TA spectra of the iodide complexes show a transient absorption between 550 and 700 nm, which does not depend on the solvent but shifts to lower energy in the order iPr-DAB > bpy > iPr-PyCa. This band is assigned to an intraligand transition. For the corresponding chloride and bromide complexes this band occurs at higher energy, most probably because of a change of character of the lowest excited state from XLCT to MLCT. The TRIR spectra show an increase in v(CO) (and k(CO)) on promotion to the excited state; however, the shifts Delta v(CO) show a decrease in the order Cl- > Br- > I-. The TR(3) spectra of the excited complexes [Ru(X)(R)(Co)(2)(iPr-DAB)] show v(s)(CN) of the iPr-DAB ligand 50-80 cm(-1) lower in frequency than for the complexes in their ground state. This frequency shift decreases in the order Cl- > Br- > I-, indicating a decrease of CT character of the lowest excited state in this order. However, going from X = Br to I, the effect on Delta v(CO) is much larger than the decrease of Delta v(s)(CN). This different effect on the CO- and CN-stretching frequencies is assigned to a gradual change in character of the lowest excited state from MLCT to XLCT when Cl- is replaced by Br- and I-. This result confirms a similar conclusion derived from previous resonance Raman and emission experiments on these complexes.