Photoionization method

Watanabe, K., Nakayama, T., and Mottl, J. (1959). Final Report on Ionization Potentials of Molecules by a Photoionization Method, Dept. Aimy No. 5B-99-01-004, ORD TB2-0001-00R-1624. 

Decay of OaOAj) in presence of steady-state 03 concentration. Photoionization method 48... 

Recent advances in experimental techniques, particularly photoionization methods, have made it relatively easy to prepare reactant ions in well-defined states of internal excitation (electronic, vibrational, and even rotational). This has made possible extensive studies of the effects of internal energy on the cross sections of ion-neutral interactions, which have contributed significantly to our understanding of the general areas of reaction kinetics and dynamics. Other important theoretical implications derive from investigations of the role of internally excited states in ion-neutral processes, such as the effect of electronically excited states in nonadiabatic transitions between two potential-energy surfaces for the simplest ion-molecule interaction, H+(H2,H)H2+, which has been discussed by Preston and Tully.2 This role has no counterpart in analogous neutral-neutral interactions. 

In a further refinement of the photoionization method the kinetic energy of the photoelectrons produced is measured in coincidence with the photoion current this is the so-called photoion photoelectron coincidence (PIPECO) method. By this method, reactions of state selected ions can be direcdy monitored. This technique has been successfully applied to study... 

With more conventional photoelectron spectroscopy (PES), the photon energy is fixed and the distribution of kinetic energies of the electrons produced by photoionization determined. The latter distribution reflects the distribution of ion internal states produced. Photoelectron spectroscopy has been applied to determine vibrational-state distributions at the same photon wavelengths at which an ion-molecule reaction was studied using photoionization methods (Fig. 4).86d... 

Photoionization has been most successfully applied to study of the effects of reactant vibrational energy on the cross sections of exothermic and endothermic ion-molecule reactions. Reactions studied by this method are summarized in Table II. In addition, photoionization methods... 

Dithiiranethione is an isomer of CS3 and its preparation and structure have been drawing much attention [75JCS(P2)559]. In the chemiionization process of CS + CS2 using the molecular beam photoionization method, the photoionization efficiency curve of CSJ was observed (80JCP4242). 

Two general methods have been proposed for separating uranium isotopes. In the photoionization method to be discussed in Sec. 9.2, in uranium metal vapor is ionized selectively and then separated from unionized by deflection in electric or magnetic fields. In the photochemical method, to be described in Sec. 9.3, UFj in UFj vapor is excited selectively and caused to react chemically to produce a solid lower fluoride, which is then separated from unreacted UF5 vapor. 

There are a number of advantages of the photoionization method for generating radical cations for kinetic studies. For... 

As mentioned above, photoionization methods usually lead to more accurate results than the electron impact... 

NO + impurity + CH3I (Reprinted with permission from [8]. Photoionization method was used to form the free electrons, and the drift gas was maintained at atmospheric temperature. These spectra were averaged ovct 20 scans, and the drift times were adjusted for a uniform drift potential of —500 V)... 

Special interfaces are used for highly specialized tasks. For example, Sloane and Rat-cliffe [207] devised an instrument for molecular beam sampling of transient combustion phenomena by TRMS. It was possible to detect various flame components with good spatial and temporal resolution [207]. Reaction kinetics and the chemistry of low-pressure flames was studied with aid of a photoionization method [208]. 

The high sensitivity of the photoionization method is very useful for the spectroscopy of very rare elements whose spectral properties are not well known. One such element is francium (Fr), the natural abundance of which is extremely low (1 Fr atom is found in 3 X 10 atoms of natural uranium), and which is formed as a result of the decay of In our experiments (Andreyev et al. 1987, 1988), the resonance photoionization technique was used to detect Fr atoms and study their Rydberg states. The atoms... 

A universal way to overcome this difficulty and make the multistep resonance photoionization method actually applicable to the detection of rare isotopes was suggested by Kudriavtzev and Letokhov (1982). The idea of the method is based on the collinear stepwise photoionization of a beam of accelerated atoms. The acceleration of the atoms in the form of ions under a given potential difference U with subsequent neutralization of the ions into atoms leads to bunching of the longitudinal ionic velocities, and hence to narrowing of the Doppler width of all the spectral lines of the given atomic species (if viewed in a collinear fashion), as compared with the initial Doppler width at... 

Ng CY (1998) State-selected and state to state ion-molecule reaction dynamics by photoionization methods. In Farrar JM and Saunders WHJ (eds) Techniques for the Study of Ion-Molecule Reactions, 417-488. New York Wiley. 

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