Mass-analysed threshold ionization

A study of the elimination of Cl from 2-chlorobutane on irradiation at 193 nm has been reported. " The photodissociation of jet-cooled CH3CF2CI at 235 nm has been studied, " as has the photodissociation of iodobutane. This latter work used vacuum-UV mass-analysed threshold ionization. Media of different polarity and viscosity have been used in a study of the photochemical behaviour of... 

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. 

MATI Mass-analysed threshold ionization UVAHJV Ultraviolet/vacuum ultraviolet... 

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. 

Haines S, Dessent C and Muller-Dethlefs K Mass analysed threshold ionization of phenol-CO, intermolecular binding energies of a hydrogen bonded complex. Journal of Chemical Physics (submitted). 

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. 

This sample has been discussed elsewhere [78,79,92]. Table 33.1 shows the elemental analyses of the sample and the fractions, while Table 33.2 shows the proportions of the maltene and asphaltene fractions. Figure 33.7 shows LD-MS of a distillation residue of Syncrude sweet blend from the Athabasca tar sands, at different LPs and different HMA voltages (9 and 10 kV). At 30% LP, the spectra (1 and 2) were very weak and close to the ionization threshold at 40% LP, the maximum ion intensity shifted slightly to higher mass (m/z 300-400) and the upper mass limit moved to about m/z 5000 at 50% LP, the maximum ion intensity remained between 300 and 400 though off-scale, while the upper mass limit moved to m/z 20,000-30,000 with evidence of cluster ion formation. Figure 33.8 shows the Syncrude mass... 

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