Spectroscopy MATI

I have had many important co-workers in this work, who not only supplied the actual calculations but many of the ideas. Certainly Dan Edwards (Idaho) who did much of the work on the monomers, and some of the dimer work. Mati Karelson (Tartu) was important in helping to develop the reaction field model for spectroscopy. Mark Thompson (PNL) did all the calculations on the RC that are discussed in this manuscript, and Marshall Cory (QTP, Florida) is carrying on this tradition. 

Characterization of the intermolecular vibrations of molecular clusters in their neutral excited and cationic states, and the study of intra-cluster ion-molecule reactions, using the techniques of REMPI, mass-analysed threshold ionization (MATI) and zero kinetic energy (ZEKE) spectroscopy. 

It should be noted that it is also possible to excite ZEKE states and to extract the corresponding ions, rather than the electrons these are then analysed in a mass spectrometer. In this case the method is called MATI (mass-analysed threshold ionization). The advantage of MATI spectroscopy is that mass resolution enables unambiguous identification of the ionized species, as well as allowing for the identification of fragmentation pathways in the ion. 

ZEKE and MATI spectroscopy, and some representative examples for their application, are discussed in further detail in Chapter 18. 

The extension of this technique to ions is somewhat complicated. The difficulty is due to the higher mass of the ions. In order to distinguish between ions formed by the electric field pulse and those formed by the laser pulse, longer pulses are needed. This spectroscopy is called mass-analysed threshold ionization (MATI). The main benefit of this method is the possibility of recording the spectra of various fragment ions together with that of the parent ion. 

An extension of ZEKE spectroscopy is mass-analysed threshold ionization (MATI), photoelectron spectroscopy without photoelectrons . This is effectively the same experiment for every ZEKE electron produced, there must be a cation, and in MATI detection a signal is recorded from these ions. It is much harder to separate the ions produced from pulsed-field ionization of the ZEKE Rydberg states from the ever-present directly produced ions. Ions are much heavier than electrons and hence move more slowly, so a higher-voltage extraction pulse is required for the separation and the subsequent extraction and selection of the cations. The obvious advantage of this combination of ZEKE with mass spectrometry is the ability to select the cations on the basis of their mass. 

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