An integrated ion trap for the photon-ion spectrometer at PETRA III.

We have added a multipole ion trap to the existing photon-ion spectrometer at PETRA III (PIPE). Its hybrid structure combines a ring-electrode trap with a segmented 16-pole trap. The interaction of gases and ions with extreme ultraviolet radiation from the beamline P04 is planned to be investigated with the newly installed multipole trap. The research focus lies on radiation-induced chemical reactions that take place in the interstellar medium or in the atmospheres of planets, including natural as well as man-made processes that are important in the Earth's atmosphere. In order to determine the mass-to-charge ratio of the stored ions as efficiently as possible, we are using an ion time-of-flight spectrometer. With this technique, all stored ions can be detected simultaneously. To demonstrate the possibilities of the trap setup, two experiments have been carried out: The photoionization of xenon and the ion-impact ionization of norbornadiene. This type of ion-impact ionization can, in principle, also take place in planetary atmospheres. In addition to ionization by photon or ion impact, chemical reactions of the trapped ions with neutral atoms or molecules in the gas phase have been observed. The operation of the trap enables us to simulate conditions similar to those in the ionosphere.

Vibrationally Resolved Inner-Shell Photoexcitation of the Molecular Anion C2.

Carbon 1s core-hole excitation of the molecular anion C2 - 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 σ u → 3 σ g ${1\sigma _u \to 3\sigma _g }$ and 1 σ g → 1 π u ${1\sigma _g \to 1\pi _u }$ core excitations of the C2 - ground level and first excited level, respectively. A detailed Franck-Condon analysis reveals a strong contraction of the C2 - molecular anion by 0.2 Šupon 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 C2 - 1 σ u - 1 3 σ g 2 2 Σ u + ${1\sigma _u^{ - 1} \,3\sigma _g^2 \;^2 \Sigma _u^ + }$ and 1 σ g - 1 3 σ g 2 2 Σ g + ${1\sigma _g^{ - 1} \,3\sigma _g^2 \;^2 \Sigma _g^ + }$ core-excited levels.

Disentangling the Photodissociation Dynamics of the 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.

Multiple Photodetachment of Carbon Anions via Single and Double Core-Hole Creation.

We report on new measurements of m-fold photodetachment (m=2-5) of carbon anions via K-shell excitation and ionization. The experiments were carried out employing the photon-ion merged-beams technique at a synchrotron light source. While previous measurements were restricted to double detachment (m=2) and to just the lowest-energy K-shell resonance at about 282 eV, our absolute experimental m-fold detachment cross sections at photon energies of up to 1000 eV exhibit a wealth of new thresholds and resonances. We tentatively identify these features with the aid of detailed atomic-structure calculations. In particular, we find unambiguous evidence for fivefold detachment via double K-hole production.

Near-K-Edge Double and Triple Detachment of the F

Double and triple detachment of the F^{-}(1s^{2}2s^{2}2p^{6}) 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 photodouble detachment with a subsequent single-Auger process in the reaction channel leading to F^{2+} 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.