C.D. Caldwell

Evidence for atomic features in the decay of resonantly excited molecular oxygen

Abstract Resonance K auger spectra of molecular oxygen are presented at photon energies corresponding to 1σ→1π g (π*), 3σ u (σ*), and Rydberg excitations. Atomic-like Auger lines observed in the 3σ u (σ*) decay spectrum are compared with the pure atomic 1s→2p resonance Auger spectrum, and evidence for very fast neutral dissociation is found. The energy shifts of “spectator” lines in the spectra measured at different excitation energies are discussed and compared with the normal O 2 K Auger spectrum.

Photoexcited K Auger spectra of atomic and molecular oxygen

Abstract K Auger spectra of the oxygen atom following either 1s photoionization or 1s → np photoexcitation are presented and compared with energy and transition rate calculations where available. Data are juxtaposed to earlier results on neon, showing that the excellent agreement between theory and experiment which exists for the closed-shell atom neon does not, at present, extend to the open-shell atom oxygen. Auger spectra following 1s → 2p excitation in the O atom and 1s, 2p double ionization in Ne are found to have similar branching ratios. All major lines in the Auger spectra of oxygen could be resolved and fully analyzed with regard to energies, branching ratios, and angular distributions. A strong anisotropy is measured for the Auger transitions associated with the 1s → 2p excitation. The 1σu → 1πg and 1σg → 3σu resonance Auger spectra of molecular oxygen are also presented. The angular distributions of the high kinetic energy lines in the molecular spectra are measured, and the atomic-like Auger lines in the 3σu decay are compared with the pure atomic 2p decay spectrum. Energies of the Kα X-ray transitions in the atom are deduced. The experimental setup, which allowed us to record these low-Z atomic Auger spectra for the first time, is described in some detail.

Outer ns,np correlation satellites in the rare gases - A photoelectron spectrometry study with an undulator photon source

Abstract High-resolution photoelectron spectra of the outer ns,np correlation satellites of neon, argon, krypton and xenon are presented for low excitation energies of about 65 eV. Relative cross-sections and photoelectron angular distribution parameters are given, and differential cross-sections at angles parallel and perpendicular to the polarization vector are included for comparison. Energy dependence of satellite features are given for neon and argon in the range 55⩽hv⩽130 eV. Results generally confirm the predictions taken from the latest theoretical interpretations, and conclusions drawn from lower-resolution data. Finally, undulator beam line characteristics have been determined and are described in some detail.

Intrinsic linewidths of neon 2s2p5(1,3P)nl2L correlation satellites

The intrinsic linewidths of 2s2p5(1,3P)3s2P and 2s2p5(1,3P)3p2S correlation satellites were determined from high resolution photoelectron spectra. The authors find widths of 0.41(5) eV for the (1P)3p2S satellite and 0.11(4) eV for the (3P)3p2S satellite. This confirms the prediction that the decay of the (1P)3p2S state is dominated by a multiplet Auger transition to the 2s2p5(3P) ionic state. The resulting broadening of the (1P)3p2S line is considerably overestimated by a relaxed single-configuration Hartree-Fock calculation, indicating the presence of strong many-electron interactions. In addition, an identification of several new lines of the conjugate shakeup 2s2p5(1P)ns2P Rydberg series and a measurement of the relative line strengths of the satellite excitations are presented.

Near threshold 4d photoexcitation and photoionization of Xe

The angular distribution parameters beta of the N5-02,3O2,3 Auger lines has been measured between the 4d5/2 and the 4d3/2 thresholds of Xe using the CIS technique. The radiationless decay parameter alpha 2 for each of the N5-O2,3O2.3 Auger lines and the alignment parameter A20 for the intermediate ion were also determined. Comparisons with previous values of beta and alpha 2 for the N5-O2.3O2.3 Auger lines have been made. In addition, shakeoff to the various states of the Xe2+ 5p4 ion has been measured following 4d photoexcitation and found to be small. These results support the contention that near-zero kinetic energy electrons observed following similar photoexcitation in the rare gases result primarily from a two-step process rather than the direct process of shakeoff.

Electron-emission analysis of the 2p4(1D)ns,nd Rydberg excitations in atomic fluorine

We have observed the autoionizing Rydberg series converging to the F+ 2p4(1D2) limit by way of photoelectron spectrometry with synchrotron radiation using a monochromator bandpass of 0.012 nm. The energy data are in good agreement with earlier results. The relative intensity of the 2p4(1S)3s(2S1/2) feature arising from the 2P3/2 ground state was found to be small, and previous discrepancies concerning this resonance could not be resolved.

High-resolution electron spectrometry of open-shell atoms

Abstract Recent progress in the study of the halogen atoms by means of electron spectrometry with the use of synchrotron radiation is described, and the autoionization features in these open-shell atoms are compared with those in the neighboring rare gas atoms. In addition, photoionization of the oxygen atom is examined at the multiplet level, and a first ion-yield measurement of the photoexcitation of the K-electron in the O atom is described.

Observation of the 2p4(1S)ns, md excitations in atomic fluorine

Abstract In the first observation of the autoionizing resonances converging to the 2p 4 ( 1 S) series limit of atomic fluorine, the decay of the resonance states into the ( 1 D) el partial channel has been measured by photoelectron spectrometry with the use of synchrotron radiation. We present the initial results of this work.