S. W. J. Scully

K-shell photoionization of ground-state Li-like carbon ions [C3+]: experiment, theory and comparison with time-reversed photorecombination

Absolute cross sections for the K-shell photoionization of ground-state Li-like carbon [C3+(1s22s 2S)] ions were measured by employing the ion?photon merged-beams technique at the Advanced Light Source. The energy ranges 299.8?300.15?eV, 303.29?303.58?eV and 335.61?337.57?eV of the [1s(2s2p)3P]2P, [1s(2s2p)1P]2P and [(1s2s)3S 3p]2P resonances, respectively, were investigated using resolving powers of up to 6000. The autoionization linewidth of the [1s(2s2p)1P]2P resonance was measured to be 27 ? 5?meV and compares favourably with a theoretical result of 26?meV obtained from the intermediate coupling R-matrix method. The present photoionization cross section results are compared with the outcome from photorecombination measurements by employing the principle of detailed balance.

K-shell photoionization of ground-state Li-like boron ions [B2 +]: experiment and theory

Absolute cross sections for the K-shell photoionization of ground-state Li-like boron [B2 +(1s22s 2S)] ions were measured by employing the ion–photon merged-beams technique at the Advanced Light Source synchrotron radiation facility. The energy ranges 197.5–200.5 eV, and 201.9–202.1 eV of the [1s(2s2p)3P]2Po and [1s(2s2p)1P] 2Po resonances, respectively, were investigated using resolving powers of up to 17 600. The energy range of the experiments was extended to about 238.2 eV yielding energies of the most prominent [1s(2l nl)]2Po resonances with an absolute accuracy of the order of 130 ppm. The natural linewidths of the [1s(2s2p)3P] 2Po and [1s(2s2p)1P] 2Po resonances were measured to be 4.8 ± 0.6 meV and 29.7 ± 2.5 meV, respectively, which compare favourably with theoretical results of 4.40 meV and 30.53 meV determined using an intermediate-coupling R-matrix method.

Lifetime of a K-shell vacancy in atomic carbon created by 1s → 2p photoexcitation of C+

Lifetimes for K-shell vacancy states in atomic carbon have been determined by measurement of the natural linewidth of the 1s → 2p photoexcited states of C + ions. The K-shell vacancy states produced by photoionization of atomic carbon are identical to those produced by 1s → 2p photoexcitation of a C + ion: 1s2s 2 2p 22 D, 2 P, and 2 S autoionizing states occur in both cases. These vacancy states stabilize by emission of an electron to produce C 2+ ions. Measurements are reported for the lifetime of the 1s2s 2 2p 22 D, 2 P and 2 S autoionizing states of C + :6 .3± 0.9 fs, 11.2 ± 1.1 fs and 5.9 ± 1.3 fs respectively. Knowledge of such lifetimes is important for comparative studies of the lifetimes of Kshell vacancies in carbon-containing molecules, benchmarking theory, and interpreting satellite x-ray spectra from astrophysical sources such as x-ray binaries. Absolute cross sections were measured for both ground-state and metastable-state ions providing a stringent test of state-of-the-art theoretical calculations. Carbon is ubiquitous in nature and is the building block of life. This atom in its various stages of ionization has relatively few electrons, and is thus amenable to theoretical study. Lifetimes

K-shell photoionization of Be-like boron (B+) ions: experiment and theory

Absolute cross sections for the K-shell photoionization of Be-like boron ions were measured with the ion–photon merged-beams technique at the Advanced Light Source synchrotron radiation facility. High-resolution spectroscopy with E/ΔE up to 8800 (ΔE ~ 22 meV) covered the energy ranges 193.7–194.7 eV and 209–215 eV. Lifetimes of the strongest resonances are determined with relative uncertainties down to approximately 4% for the broadest resonance. The measured resonance strengths are consistent with 60% 1s22s2 1S ground-state and 40% 1s22s2p 3Po metastable-state ions in the primary ion beam and confirmed by comparison with independent absolute photo-recombination heavy-ion storage-ring measurements with B2 + ions using the principle of detailed balance. Experimental determination of the line width for the 1s2s22p 1Po resonance gives a value of 47 ± 2 meV and compares favourably to a theoretical estimate of 47 meV from the R-matrix with pseudo-states (RMPS) method. The measured line widths of the 1s2s2p2 3P, 3D resonances are 10.0 ± 2 meV and 32 ± 3 meV, respectively, compared to RMPS theoretical estimates of 9 meV and 34 meV.

K-shell photoionization of Be-like carbon ions : experiment and theory for C2+

Absolute cross-section measurements for K-shell photoionization of Be-like C2+ ions have been performed in the photon energy range 292 325 eV. These measurements have been made using the photon ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory. Absolute measurements compared with theoretical results from the R-matrix method indicate that the primary C2+ ion beam consisted of 62 percent ground-state (1s22s2 1S) and 38 percent metastable state (1s22s2p 3Po) ions. Reasonable agreement is seen between theory and experiment for absolute photoionization cross sections, resonance energies and autoionization line widths of K-shell-vacancy Auger states.

Threshold truncation of a 'giant' dipole resonance in photoionization of Ti3+

Photoionization of triply charged titanium ions was investigated using the merged photon–ion beam technique at a synchrotron light source. The experimental photon energy range 42.6–49.4 eV encompasses the threshold for the photoionization of Ti3+(3p6 3d2 D3/2) ground-state ions at 43.267 eV. Prominent resonance features due to 3p → 3d and 3p → 4s excitations are observed with the strongest one being the giant 3p5(3d23F)2F dipole resonance which has a width of 1.5 eV. Since it is located only 0.2 eV above the ionization threshold a cut-off of this resonance is observed in photoionization. By employing the principle of detailed balance the results are compared with an earlier experimental study of the time-reversed Ti4+ photorecombination. The comparison clarifies the giant resonances role in photorecombination and yields state-selective photoionization and photorecombinaton cross sections on an absolute scale.

Doubly excited resonances in the photoionization spectrum of Li

Absolute cross-section measurements for resonant double photoexcitation of Li+ions followed by autoionization have been performed at high resolution in the photon energy range from 148 eV, just below the (2s2p, 2(0,1)+2) resonance to 198 eV (the region of the double ionization threshold). The measurements have been made using the photon-ion merged-beam endstation at the Advanced Light Source, Lawrence Berkeley National Laboratory, USA. The absolute cross-section measurements show excellent agreement with theoretical results from the R-matrix plus pseudo-state (RMPS) method.

Negative photoion spectroscopy of the core-excited bromo-chloro-alkanes, Br(CH2)nCl, n = 1?4

Polar photodissociation of a set of bromo-chloro-alkanes in the vicinity of the Br 3d core edge has been observed for the first time. It is shown that negative photoion spectroscopy is a powerful tool for investigating the various decay mechanisms of core-excited molecules. Analysis of these results indicates that the observed polar photodissociation arises from two competing spectator Auger decay processes in which the molecule can dissociate either before or after the core hole relaxation.

K-shell photoionization of Be-like B+ ions

Absolute cross sections for K-shell photoionization of Be-like B+ ions were measured employing the photon-ion merged-beam technique at the Advanced Light Source in Berkeley. The results are found to be in fair agreement with R-matrix calculations using L-S coupling.

Photoionization measurements for the iron isonuclear sequence Fe{sup 3+}, Fe{sup 5+}, and Fe{sup 7+}

Cross sections for single photoionization of Fe{sup 3+}, Fe{sup 5+}, and Fe{sup 7+} ions were measured at spectral resolutions of 0.04, 0.15, and 0.13 eV, respectively, by merging mass- and charge-selected ion beams with a beam of monochromatized synchrotron undulator radiation. The measurements span photon energy ranges beginning at the ionization thresholds and extending several tens of electron volts to include the most important resonant contributions due to 3p-nd transitions to autoionizing states. The photoion yield spectra are characterized by narrow resonances and also broad features in Fe{sup 3+} and Fe{sup 5+} that are believed to result from unresolved fast super-Coster-Kronig transitions following 3p-3d excitation. Absolute photoionization cross-section measurements were also performed using ion beams containing undetermined fractions of ions in their ground and metastable states. A Rydberg series attributed to 3p-nd transitions from the {sup 2}G{sub 1} metastable state in Fe{sup 3+} was identified. The data are compared with recently published measurements on Fe{sup 3+} and Fe{sup 5+} using a similar technique at lower spectral resolution.