This paper reports on a newly developed mobile mass spectrometer for comprehensive on-line analysis of complex gas mixtures such as ambient air or industrial process gases. Three ionization methods, namely, the resonance-enhanced multiphoton ionization (REMPI), vacuum-ultraviolet single-photon ionization (SPI), and electron impact ionization (EI) are implemented in this instrument and can be operated (quasi-) simultaneously. By means of this setup, a wide range of compounds can be analyzed due to the unique ionization selectivitiy and sensitivity profiles provided by the different ionization techniques. The mass spectrometer is designed for field application even under severe conditions. The REMPI technique is suitable for the selective and soft ionization (without fragmentation) of aromatic compounds at trace level (ppbv/pptv). The also soft but less selective SPI technique with 118-nm vacuum-ultraviolet laser pulses is used as a second laser-based ionization method. Mass spectra obtained by this technique show profiles of most organic compounds (aliphatic and aromatic species) and of some low IP inorganic substances (e.g., ammonia, nitrogen oxide) down to ppbv concentrations. In addition to the laser-based ionization techniques, EI ionization can be used for analysis of the bulk components such as water, oxygen, nitrogen, and carbon dioxide as well as for detection of inorganic minor components such as HCN or HCl from combustion flue gases at ppmv concentration levels. Each method yields specific mass spectrometric information of the sample composition. Special techniques have been developed to combine the three ionization methods in a single mass spectrometer and to allow the quasi-parallel application of all three ionization techniques.

A photoionization experiment on free oriented molecules in the gas phase has been performed. CH3I molecules in a supersonic beam have been oriented with respect to the molecular axis parallel to an external field by use of an electric hexapole. The photoelectrons ejected by vacuum ultraviolet radiation in a region of a very weak field from the lone-pair orbital located at the iodine atom show a pronounced asymmetry depending on whether electrons are emitted parallel or antiparallel to the molecular axis.PACS numbers: 33.80.Eh, 33.60.CvRecent photoemission experiments with atoms, 1 molecules, 2 or solids 3 have shown that details of the photoionization dynamics can be obtained if the photoelectron spectroscopy studies are performed in an angular-and/or even spin-resolved manner. In molecular photoionization, however, still much detailed information was hidden because only randomly oriented molecules could be photoionized in previous gas-phase experiments. Theoretical investigations into the study of photoelectron emission of free oriented molecules became very important and have been successfully performed 4 " 8 after there was experimental evidence 9 that photoemission from molecules chemisorbed on a solid-state surface reflects the orientation of the molecules with respect to the surface. To close the gap between photoionization of randomly oriented molecules in the gas phase and of oriented molecules in the chemisorption requires experimental studies of the influence of the molecular orientation onto the molecular photoemission process. We present for the first time experimental results of an angular-resolved photoelectron spectroscopy study on free oriented molecules in the gas phase.Diatomic closed-shell molecules with permanent electric dipole moment /x rotate perpendicularly to /x, so that their orientation requires enormous electric fields (~~ 10 7 V/cm) to overcome the rotational inertia of the molecules. 10 " 12 However, symmetric top molecules like CH 3 I can have rotational states, where the rotational momentum J has a component parallel to /ut, i.e., symmetric tops in these rotational states can be oriented in lower electric fields, which is a critical requirement in our photoionization experiment. The experimental technique corresponds to an ''electrostatic Stern-Gerlach method" 10 " 14 with use of an electrostatic hexapole. Figure 1 shows the schematic setup of the apparatus. The vacuum ultraviolet (VUV) lamp 15 and the cylindrical-mirror-analyzer electron spectrometer are necessary for photoelectron spectroscopy. The main parts of the source of oriented molecules are the supersonic beam source, the electrostatic hexapole, and the guiding field; in between a buffer field is placed. The interaction energy of a CH 3 I molecule with an electric field E is 13where 9 is the angle between /JL and E, and 7, K, and Mj are the rotational quantum numbers. 14 The force G = -grad H^S tark onto the molecules in the inhomogeneous electric field of the hexapole separates molecules with different orientation of the...

Strongly peaked electron density profiles have been obtained in ASDEX by different refuelling methods: pellet fuelling (ohmic and co-injection heating), NBI counter-injection and recently by reduced gas puff fuelling scenarios. These discharges show in common increased density limits, a canonical electron temperature profile independent of the density profile and an improvement of the particle and energy confinement. Whereas the changes in particle transport are not fully understood, transport analyses point out that the improved energy transport can be explained by reduced ion conduction losses coming close to the neoclassical ones. The different results for the ion transport with flat and peaked density profiles are quantitatively consistent with that expected from qi-driven modes. The analyses cannot yet explain the anomalous electron energy transport, apart from identified continuous trends such as inverse scaling with the isotope mass and enhancement with heating power.

No abstract

No abstract