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 2 2 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 2 2 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
We have investigated photoionization (PI) of the 1S ground
state and 3Po metastable states of C2+ ions in
the photon energy range 40.8-56.9 eV at a resolution of 30 meV.
Absolute PI cross sections have been measured using a photon-ion
merged beam arrangement at the Advanced Light Source.
Detailed calculations using the semi-relativistic Breit-Pauli
R-matrix approach suggest a fraction of 40% of metastable
ions in the primary beam of the experiment. The present results
are discussed in the light of previous electron-C3+-ion
photorecombination (PR) studies. As an example, the role of the
intermediate C2+(2p4d 1P) resonance in both PI and PR
is analysed.
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 resonance's role in photorecombination and yields state-selective photoionization and photorecombinaton cross sections on an absolute scale.
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