Condenser photoionization

Figure 1. Schematic illustration of the laser-vaporization supersonic cluster source. Just before the peak of an intense He pulse from the nozzle (at left), a weakly focused laser pulse strikes from the rotating metal rod. The hot metal vapor sputtered from the surface is swept down the condensation channel in dense He, where cluster formation occurs through nucleation. The gas pulse expands into vacuum, with a skinned portion to serve as a collimated cluster bean. The deflection magnet is used to measure magnetic properties, while the final chaiber at right is for measurement of the cluster distribution by laser photoionization time-of-flight mass spectroscopy.

The cluster reactor is attached to the pulsed cluster source s condensation channel, as shown in Figure 6. (16) To it is attached a high-pressure nozzle from which a helium/hydrocarbon mixture is pulsed into the reactor at a time selected with respect to the production and arrival of the clusters. The effect of turbulent mixing with the reactant pulse perturbs the beam, but clusters and reaction products which survive the travel from the source to the photoionization regime ( 600y sec) and the photoionization process are easily detected. 

Despite many synthetic efforts no P- or As-cluster cations have been characterized in condensed phases to date, although their existence in the gas phase is well established by mass spectrometry and photoionization in combination with quantum chemical calculations (see below). Only one antimony cation is claimed in con-... 

Ultracold neutral plasmas may be produced by laser cooling and trapping of different types of neutral atoms [105] such as calcium, strontium, rubidium, cesium etc., by photoionizing Bose condensates [106] and also by spontaneous ionization of dense Rydberg atoms [107,108]. A review on ultracold neutral plasmas due to Killan et al. [61] gives an excellent disposition on the subject. 

Silylenium ions are common in gas-phase organosilicon chemistry, where they may be generated by various techniques including electron impact (29-33), photoionization (34-36), chemical ionization (37-45), collision-induced dissociation (25,46), and chemical-nuclear methods (15). Although this article is concerned with reactions in solution, a short account of gas-phase studies cannot be omitted, since they provide important information about chemical and physical properties of silylenium ions, which are so elusive in condensed phases. 

The spectra of atoms are characterized by a set of bound Rydberg states below the photoionization threshold for excitations in the continuum " The Rydberg states become very weak in molecules and disappear in condensed systems. Review papers on x-ray absorption spectra for atoms and molecules are available and these spectra will not be discussed here. 

Inner-shell photoionization of atoms, molecules, clusters, and the condensed phase cannot be simply described by one electron photoemission, assuming frozen orbital energies. This simple approach, which corresponds to Koopmans theorem, is often successfully applied to describe valence-shell photoionization. However, this approach completely fails for inner-sheU photoionization, where deviations of the order of 10-20 eV relative to the experimental results are found. 

Finally we consider the creation of a charged particle, e.g., by photoionization inside the plate condenser. This process is shown in Fig. 5.6. When a neutral particle is in the condenser, we do not care about the electric potential therein. So we ideally neglect electric polarization of the particle. When the particle dissociates into ions, without any kinetic energy, then these ions are finding themselves in a region of some electric potential. It is suggestive that the work of ionization is dependent on the electric potential in the region where the ions are created. 

Ionization of condensed-phase analytes occurs by mixing a sample in a suitable matrix and bombarding the matrix-analyte mixture with an energetic beam made of either laser photons as in MALDI, high-energy fission particles as in Cf plasma desorption, or high-energy fast atoms or ions (FAB or liquid SIMS). When an analyte is present in a solution, such as an effluent from a separation device, it can be ionized via thermospray ionization, atmospheric-pressure chemical ionization, atmospheric-pressure photoionization, or electrospray ionization. Desorption electrospray ionization and direct analysis in real time are new modes of ionization that are accomplished in ambient air. 

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