Abstract
Carbon 1s excitation of methane, CH
4
, has been studied in the gas phase using the ion trap integrated with the photon–ion instrument at PETRA III/DESY and soft X-rays from the beamline ...P04. The created photoions are stored within the ion trap so that in further steps the photoions can undergo reactions with neutral methane molecules. The ionic photoproducts as well as reaction products created thereby are mass-over-charge analyzed by an ion time-of-flight spectrometer. Besides the photoions, product ions with up to three carbon atoms are found. In contrast to experiments using vacuum ultraviolet radiation, especially highly reactive product ions with a small number of hydrogen atoms such as
C
2
H
2
+
and
C
2
H
3
+
are found, which are important precursors for larger hydrocarbons such as C
6
H
6
. Possible production routes of the product ions are analyzed on the basis of a model that considers the probabilities for photofragmentation and the first subsequent chemical reaction step. The model indicates that the high degree of fragmentation by photons with energies around 280 eV is favoring these products. The results of the measurements show that the products like
C
2
H
2
+
and
C
2
H
3
+
can be generated by a single collision of the ionization product with neutral methane. The results suggest that soft X-rays might be important for chemical reactions in planetary atmospheres, which has usually not been taken into account. However, due to the high degree of fragmentation and large cross sections involved, they can have a large influence even when the corresponding photon flux is rather small.
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.
We review the recent experimental and theoretical progress in K-shell detachment studies of atomic anions. On the experimental side, this field has largely benefitted from technical advances at 3rd ...generation synchrotron radiation sources. For multiple detachment of C−, O−, and F− ions, recent results were obtained at the photon-ion merged-beams setup PIPE which is a permanent end station at beamline P04 of the PETRA III synchrotron light source in Hamburg, Germany. In addition to a much increased photon flux as compared to what was available previously, the PIPE setup has an extraordinary detection sensitivity for heavy charged reaction products that allows one to study detachment processes with extremely low cross sections in the kilobarn range, e.g., for processes involving the simultaneous creation of two core-holes by a single photon as observed in the net triple detachment of F− and the net five-fold detachment of C−. Moreover, hitherto disregarded photodetachment resonances have been discovered, which exhibit a variety of line shapes. For O− the core-hole lifetime could be determined precisely from a high-resolution measurement of a photodetachment resonance. These experimental findings pose new challenges for state-of-the-art atomic theory and require calculations combining photoexcitation (ionization) with decay cascade processes that follow after initial core-hole production.
Single, double, and triple ionization of C(1+) ions by single photons is investigated in the energy range of 286-326 eV, i.e., in the range from the lowest-energy K-vacancy resonances to well beyond ...the K-shell ionization threshold. Clear signatures of C(1+)(1s2s(2)2p(2) (2)D,(2)P) resonances are found in the triple-ionization channel. The only possible mechanism producing C(4+)(1s(2)) via these resonances is direct triple-Auger decay, i.e., a four-electron process with simultaneous emission of three electrons.
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
1σu→3σg
${1\sigma _u \to 3\sigma _g }$
and
1σg→1πu
${1\sigma _g \to 1\pi _u }$
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 Å 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 C2−
1σu-13σg22Σu+
${1\sigma _u^{ - 1} \,3\sigma _g^2 \;^2 \Sigma _u^ + }$
and
1σg-13σg22Σg+
${1\sigma _g^{ - 1} \,3\sigma _g^2 \;^2 \Sigma _g^ + }$
core‐excited levels.
Strong contraction: The C2− molecular anion shrinks when it absorbs an X‐ray photon.
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.
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.
Aim
To develop test methods and evaluate survival of Bacillus thuringiensis kurstaki cry− HD‐1 and B. thuringiensis Al Hakam spores after exposure to hot, humid air inside of a C‐130 aircraft.
...Methods and Results
Bacillus thuringiensis spores were either pre‐inoculated on 1 × 2 or 2 × 2 cm substrates or aerosolized inside the cargo hold of a C‐130 and allowed to dry. Dirty, complex surfaces (10 × 10 cm) swabbed after spore dispersal showed a deposition of 8–10 log10 m−2 through the entire cargo hold. After hot, humid air decontamination at 75–80°C, 70–90% relative humidity for 7 days, 87 of 98 test swabs covering 0·98 m2, showed complete spore inactivation. There was a total of 1·67 log10 live CFU detected in 11 of the test swabs. Spore inactivation in the 98 test swabs was measured at 7·06 log10 m−2.
Conclusions
Laboratory test methods for hot, humid air decontamination were scaled for a large‐scale aircraft field test. The C‐130 field test demonstrated that hot, humid air can be successfully used to decontaminate an aircraft.
Significance and Impact of the Study
Transition of a new technology from research and development to acquisition at a Technology Readiness Level 7 is unprecedented.
Synopsis We report on measured oxygen K-LL Auger spectra induced by 1.5-keV electron impact on O2, CO2, and N2O gaseous targets. An ESA-22-type electron spectrometer was employed which is capable of ...simultaneous energy and angular analysis covering a polar angular range of 15° to 345°. The measurements were carried out in preparation for future experiments with more complex chiral molecular targets and a spin-polarized electron source. The present experimental data are compared with results from earlier experimental studies.
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