| 1. |
- Gisselbrecht, Mathieu, et al.
(författare)
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Size dependent fragmentation of argon clusters in the soft x-ray ionization regime.
- 2008
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Ingår i: Journal of Chemical Physics. - : AIP Publishing. - 0021-9606 .- 1089-7690. ; 128:4
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Tidskriftsartikel (refereegranskat)abstract
- Photofragmentation of argon clusters of average size ranging from 10 up to 1000 atoms is studied using soft x-ray radiation below the 2p threshold and multicoincidence mass spectroscopy technique. For small clusters (N=10), ionization induces fast fragmentation with neutral emission imparting a large amount of energy. While the primary dissociation takes place on a picosecond time scale, the fragments undergo slow degradation in the spectrometer on a microsecond time scale. For larger clusters (N>/=100) we believe that we observe the fragmentation pattern of multiply charged species on a time-scale which lasts a few hundred nanoseconds. The reason for these slower processes is the large number of neutral atoms which act as an efficient cooling bath where the excess energy ("heat") dissipates among all degrees of freedom. Further degradation of the photoionic cluster in spectrometer then takes place on the microsecond time scale, similar to small clusters.
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| 2. |
- Schnadt, Joachim, et al.
(författare)
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The new ambient-pressure X-ray photoelectron spectroscopy instrument at MAX-lab
- 2012
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Ingår i: Journal of Synchrotron Radiation. - 0909-0495 .- 1600-5775. ; 19, s. 701-704
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Tidskriftsartikel (refereegranskat)abstract
- The new instrument for near-ambient-pressure X-ray photoelectron spectroscopy which has been installed at the MAX II ring of the Swedish synchrotron radiation facility MAX IV Laboratory in Lund is presented. The new instrument, which is based on a SPECS PHOIBOS 150 NAP analyser, is the first to feature the use of retractable and exchangeable high-pressure cells. This implies that clean vacuum conditions are retained in the instrument's analysis chamber and that it is possible to swiftly change between near-ambient and ultrahigh-vacuum conditions. In this way the instrument implements a direct link between ultrahigh-vacuum and in situ studies, and the entire pressure range from ultrahigh-vacuum to near-ambient conditions is available to the user. Measurements at pressures up to 10(-5) mbar are carried out in the ultrahigh-vacuum analysis chamber, while measurements at higher pressures are performed in the high-pressure cell. The installation of a mass spectrometer on the exhaust line of the reaction cell offers the users the additional dimension of simultaneous reaction data monitoring. Moreover, the chosen design approach allows the use of dedicated cells for different sample environments, rendering the Swedish ambient-pressure X-ray photoelectron spectroscopy instrument a highly versatile and flexible tool.
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| 3. |
- Werner, Josephina, et al.
(författare)
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Surface Behavior of Hydrated Guanidinium and Ammonium Ions : A Comparative Study by Photoelectron Spectroscopy and Molecular Dynamics
- 2014
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Ingår i: Journal of Physical Chemistry B. - : American Chemical Society (ACS). - 1520-6106 .- 1520-5207. ; 118:25, s. 7119-7127
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Tidskriftsartikel (refereegranskat)abstract
- Through the combination of surface sensitive photoelectron spectroscopy and molecular dynamics simulation, the relative surface propensities of guanidinium and ammonium ions in aqueous solution are characterized. The fact that the N Is binding energies differ between these two species was exploited to monitor their relative surface concentration through their respective photoemission intensities. Aqueous solutions of ammonium and guanidinium chloride, and mixtures of these salts, have been studied in a wide concentration range, and it is found that the guanidinium ion has a greater propensity to reside at the aqueous surface than the ammonium ion. A large portion of the relative excess of guanidinium ions in the surface region of the mixed solutions can be explained by replacement of ammonium ions by guanidinium ions in the surface region in combination with a strong salting-out effect of guanidinium by ammonium ions at increased concentrations. This interpretation is supported by molecular dynamics simulations, which reproduce the experimental trends very well. The simulations suggest that the relatively higher surface propensity of guanidinium compared with ammonium ions is due to the ease of dehydration of the faces of the almost planar guanidinium ion, which allows it to approach the water-vapor interface oriented parallel to it.
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