Near--K-edge double and triple detachment of the F- negative ion: observation of direct two-electron ejection by a single photon

Double and triple detachment of the F-(1s2 2s2 2p6) negative ion by a single photon have been investigated in the photon energy range 660 to 1000 eV. The experimental data provide unambiguous evidence for the dominant role of direct photo-double-detachment with a subsequent single-Auger process in the reaction channel leading to F2+ product ions. Absolute cross sections were determined for the direct removal of a (1s+2p) pair of electrons from F- by the absorption of a single photon

Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C2−_2^-

Carbon $1s$ core-hole excitation of the molecular anion C$_2^-$ has been experimentally studied at high resolution by employing the photon-ion merged-beams technique at a synchrotron light source. The experimental cross section for photo--double-detachment shows a pronounced vibrational structure associated with $1\sigma_u\to3\sigma_g$ and $1\sigma_g \to 1\pi_u$ core excitations of the C$_2^-$ ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C$_2^-$ molecular anion by 0.2~\AA\ upon this core photoexcitation. The associated change of the molecule's moment of inertia leads to a noticeable rotational broadening of the observed vibrational spectral features. This broadening is accounted for in the present analysis which provides the spectroscopic parameters of the C$_2^-$ $1\sigma_u^{-1}\,3\sigma_g^2\;{^2}\Sigma_u^+$ and $1\sigma_g^{-1}\,3\sigma_g^2\;{^2}\Sigma_g^+$ core-excited levels.Comment: 8 pages, 5 figures, 1 table, accepted for publication in ChemPhysChe

Multiple photodetachment of silicon anions via K -shell excitation and ionization

Experimental cross sections for $m$-fold photodetachment ($m=3-6$) of silicon anions via $K$-shell excitation and ionization were measured in the photon-energy range of 1830-1900 eV using the photon-ion merged-beams technique at a synchrotron light source. All cross sections exhibit a threshold behavior that is masked by pre-threshold resonances associated with the excitation of a $1s$ electron to higher, either partly occupied or unoccupied atomic subshells. Results from multi-configuration Dirac-Fock (MCDF) calculations agree with the experimentally derived cross sections for photo-absorption if small energy shifts are applied to the calculated resonance positions and detachment thresholds. Moreover, a systematic approach is applied for modeling the deexcitation cascades that set in after the initial creation of a $K$-shell hole. The resulting product charge-state distributions compare well with the measured ones for direct $K$-shell detachment but less well for resonant $K$-shell excitation. The present results are potentially useful for identifying silicon anions in cold plasmas such as interstellar gas clouds.Comment: 8 pages, 4 figure

Photoionization of low-charged silicon ions

Single and multiple photoionization of Si1+, Si2+, and Si3+ ions have been investigated near thesilicon K-edge using the PIPE setup at beamline P04 of the synchrotron light source PETRA III operated byDESY in Hamburg, Germany. Pronounced resonance structures are observed for all ions which are associatedwith excitation or ionization of a K-shell electron. The experimental cross sections are compared with resultsfrom theoretical calculations

Disentangling the Photodissociation Dynamics of the HF+HF^{+} Molecular Radical via Kinetic-Energy-Release-Resolved F 1s Core Excitation and Ionization

The F 1s core level photoionization of the ionic molecular radical HF+ has been studied using the photon–ion merged-beams technique at a synchrotron radiation source. Upon analyzing kinetic energy release (KER) dependent photoion yield spectra, complex ultrafast dissociation dynamics of the F 1s core hole excited σ* state can be revealed. By means of configuration–interaction electronic structure calculations of the excited molecular potential energy curves, this complex process can be attributed to a spin-dependent dissociation of the excited σ* biradical state