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We present a new high-pressure x-ray photoelectron spectroscopy system dedicated to probing catalytic reactions under realistic conditions at pressures of multiple bars. The instrument builds around the novel concept of a "virtual cell" in which a gas flow onto the sample surface creates a localized high-pressure pillow. This allows the instrument to be operated with a low pressure of a few millibar in the main chamber, while simultaneously a local pressure exceeding 1 bar can be supplied at the sample surface. Synchrotron based hard x-ray excitation is used to increase the electron mean free path in the gas region between sample and analyzer while grazing incidence <5 ○ close to total external refection conditions enhances surface sensitivity. The aperture separating the high-pressure region from the differential pumping of the electron spectrometer consists of multiple, evenly spaced, micrometer sized holes matching the footprint of the x-ray beam on the sample. The resulting signal is highly dependent on the sample-to-aperture distance because photoemitted electrons are subject to strong scattering in the gas phase. Therefore, high precision control of the sample-to-aperture distance is crucial. A fully integrated manipulator allows for sample movement with step sizes of 10 nm between 0 and −5 mm with very low vibrational amplitude and also for sample heating up to 500 ○ C under reaction conditions. We demonstrate the performance of this novel instrument with bulk 2p spectra of a copper single crystal at He pressures of up to 2.5 bars and C1s spectra measured in gas mixtures of CO + H 2 at pressures of up to 790 mbar. The capability to detect emitted photoelectrons at several bars opens the prospect for studies of catalytic reactions under industrially relevant operando conditions.Published under license by AIP Publishing. https://doi. ARTICLEscitation.org/journal/rsi FIG. 13. Mass spectrometry signal of m/z corresponding to CO (red), O 2 (blue), and CO 2 (black) and left axis. The single crystal temperature (dashed black and right axis) was ramped at a rate of 2.5 ○ C/s.

The paper presents experimental investigation of the crystallization kinetics of thin (from several and up to 100 monolayers, ML) amorphous ice films grown in a vacuum on clean and adsorbate modified Pt(111) and graphite (0001) surfaces. The crystallization kinetics was followed by the associated decrease of the desorption rate by isothermal desorption mass spectroscopy. The process is strongly substrate dependent for thin films (below 20-30 ML), gradually becoming substrate independent in 30-100 ML range, and approaching the bulk ice characteristics for thicker films. For thin films, the enthalpy of vaporization is 52 kJ/mol for the amorphous and 54 kJ/mol for the crystalline films. The activation energy for crystallization was estimated to be 75 kJ/mol. The crystallization is accompanied by an enhanced mobility in the film as demonstrated experimentally by following O2 release during crystallization of ice films on O2 precovered Pt(111).