H. Schmoranzer

Study of the B″B¯Σu+1 state of H2: Transition probabilities from the ground state, dissociative widths, and Fano parameters

The transition probabilities, the dissociation widths, and the associated Fano parameters for rovibronic lines with J=0,...,3 of the absorption bands of the BB 1Sigmau+ state out of the X 1Sigmag+ v=0 ground state were measured over the complete vibrational progression, showing clearly that only the inner-well state with B 4psigma character can absorb vuv light and predissociate efficiently. The absolute values of these transition probablities, predissociation widths, and Fano parameters were found to agree well with ab initio calculations if one takes into account that the calculations neglect nonadiabatic couplings.

Alteration of exchange anisotropy and magnetoresistance in Co/Cu/Co/FeMn spin valves by ion bombardment

The dose dependence of the exchange bias field and magnetoresistance by 10 keV-He ion bombardment in an applied magnetic field were investigated for Co/Cu/Co/FeMn top spin valves. The exchange bias field Heb of the pinned Co layer can be enhanced, reversed, and reduced similarly to an exchange biased bilayer system. Additionally, upon ion bombardment, the free Co layer couples increasingly strong to the pinned Co layer until they act magnetically as one single pinned layer. The magnetoresistance decreases exponentially with increasing ion dose, caused by a higher sheet resistance due to increasing defect density and increasing coupling between the free and the pinned ferromagnetic layer. A phenomenological model is extended to describe the ion bombardment-induced changes of Heb of ferromagnet/antiferromagnet exchange biased bilayers by including saturation effects. This model is compared to available experimental data.The dose dependence of the exchange bias field and magnetoresistance by 10 keV-He ion bombardment in an applied magnetic field were investigated for Co/Cu/Co/FeMn top spin valves. The exchange bias field Heb of the pinned Co layer can be enhanced, reversed, and reduced similarly to an exchange biased bilayer system. Additionally, upon ion bombardment, the free Co layer couples increasingly strong to the pinned Co layer until they act magnetically as one single pinned layer. The magnetoresistance decreases exponentially with increasing ion dose, caused by a higher sheet resistance due to increasing defect density and increasing coupling between the free and the pinned ferromagnetic layer. A phenomenological model is extended to describe the ion bombardment-induced changes of Heb of ferromagnet/antiferromagnet exchange biased bilayers by including saturation effects. This model is compared to available experimental data.

Neutral photodissociation of O2 Rydberg states accompanied by changes of the Rydberg electron's quantum numbers n and l

Abstract The neutral dissociation (ND) behavior of the Rydberg states converging to the c 4 Σ − u state in O2+ was investigated using photon-induced fluorescence spectroscopy (PIFS). It was found that the dissociation of Rydberg states n dσ g 3 Σ u − with v=1 and n sσ g 3 Σ u − with v=0/1 leads, in the observed fluorescence wavelength region from 90 to 105 nm, mainly to an excited OI fragment either in the ( 4 S o ) (n+1)/n s 3 S o state or ( 4 S o ) n/(n−1) d 3 D o state for the ndσg and nsσg molecular Rydberg states, respectively. The observed change of n corresponds to the conservation of the effective quantum number n ∗ .

The study of the D′Πu1 state of H2: Transition probabilities from the ground state, predissociation yields, and natural linewidths

The absorption spectrum of the H(2) molecule was studied at high resolution in the 81-72 nm spectral range. A detailed analysis of the D() (1)Pi(u)-->X (1)Sigma(g) (+) electronic band system is reported. In the spectrum, more than 70 new lines were assigned. For wavelengths longer than 75 nm, the D() (1)Pi(u) (+) and (1)Pi(u) (-) components show a clearly different behavior: Tauhe (1)Pi(u) (+) one dissociates into H(1s)+H(n=2) whereas the (1)Pi(u) (-) one leads to molecular fluorescence. For shorter wavelengths, both components are predissociated into H(1s)+H(n=3). The predissociation yields, the dissociation widths, and the absolute values of the transition probabilities were measured over the vibrational progression from v()=3 to 17, i.e., up to the dissociation limit. The comparison between these absolute transition probabilities and the values calculated in the adiabatic and nonadiabatic approximations demonstrates clearly the importance of nonadiabatic couplings.

Photoionization of Kr near the 4s threshold. I. Experiment and LS coupling theory

Absolute cross sections for the transitions of the Kr atom into the 4s1 and 4p4nl states of the Kr+ ion were measured in the 4s-electron threshold region by photon-induced fluorescence spectroscopy (PIFS). The cross sections for the transitions of the Kr atom into the 4s1 and 4p4nl states were also calculated, as well as the 4p4nlnl doubly excited states, in the frame of LS-coupling many-body technique. The cross sections of the doubly-excited atomic states were used to illustrate the pronounced contributions of the latter to the photoionization process, evident from the measurements. The comparison of theory and experiment led to conclusions about the origin of the main features observed in the experiment.

The J = 2 ortho levels of the v = 0 to 6 np singlet Rydberg series of molecular hydrogen revisited.

The energies of the J = 2 ortho levels of the v = 0 to 6 Rydberg np singlet series of molecular hydrogen with absolute intensities of the R(1) and P(3) absorption lines were measured by a high-resolution synchrotron radiation experiment and calculated through a full ab initio multi-channel quantum defect approach.

Fine-structure selectivity of neutral dissociation with excitation observed in O2

The absorption cross section of O2 and the O I (4So)3s 3So1→2p4 3PJ emission cross section were investigated near the threshold for neutral dissociation into the O I (4So)3s 3So1 state with a very narrow bandwidth (0.9 meV) of the exciting radiation. It was possible for the first time to resolve the fine-structure (FS) components of vibrational levels in the emission cross section and, in addition, to determine their relative intensities. A certain degree of selectivity in the population of FS components was observed. Furthermore, an absolute cross section for the dissociation into the fragments in the O I ground state or the metastable O I (4So)3s 5So2 state was estimated.

Structures at the Xe 5s threshold studied by photon-induced fluorescence spectroscopy

The photoionisation of Xe has been studied by photon-induced fluorescence spectroscopy (PIFS) for photon energies between 23 and 26.5 eV. The fluorescence radiation was dispersed and recorded between 103.5 and 112 nm. A prominent peak structure of the Xe 5s photoionisation cross section was observed and was attributed to two-electron excitations in neutral Xe which strongly contribute to the ionisation process.

Collisional quenching of the H(n = 3) atoms by molecular hydrogen: cross section measurements

The H(3l) + H2 collision has been investigated in the velocity range of 2-7 km s-1, at room temperature, through time-dependent fluorescence intensity measurements after pulsed excitation, at different pressures; the l-mixing cross sections and the cross sections for non-radiative quenching processes have been determined.

Perturbation theory study of triple photoionization: I. Two-step approximations in triple photoionization of Kr in the exciting-photon energy region of Kr I resonances (90 - 100 eV)

The two-step triple photoionization (TPI) process is investigated in the framework of many-body perturbation theory for the first time. Results on TPI partial cross sections from the Kr ground state to the fluorescing states of the Kr IV configuration are obtained by numerical calculations in the energy range of Kr I resonances. Several mechanisms of two-step TPI are discussed, of which the low-energy double-Auger transitions are investigated in detail. The energy distribution functions of the Auger electrons for the different orbital momenta of the ejected two Auger electrons as well as the total transition probability are presented. Comparison of the calculated TPI cross section with experimental data obtained by photon-induced fluorescence spectroscopy demonstrates quite clearly the shortcomings of the two-step approximation for a quantitative description of the process, at least in the energy region under consideration. Nevertheless qualitative agreement has been achieved which explains in principle the new fluorescence transitions in Kr IV observed after excitation of the atom by photons of an energy from 90 to 100 eV.