Collisional activation experiments ionization

It is of interest to mention some detailed mass spectrometric results that were obtained by performing distinct experiments (a) ion-molecule reactions in mixtures of haloben-zenes and ammonia under chemical ionization conditions (b) ion-molecule reactions of mass-selected ionized halobenzenes toward ammonia in a quadrupole collision cell of a hybrid tandem mass spectrometer (c) ion-molecule reactions of phenyl diazonium cations with ammonia in the same quadrupole collision cell and, finally, (d) electrospray ionization of anilines in a hybrid quadrupole-time of flight mass spectrometer (QTof). Characterization of the product ions relies on collisional activation experiments in the low or high kinetic energy regime98. 

In neutralization-reionization mass spectrometric experiments on CH2Si+ formed by electron-impact dissociative ionization of ClCH2SiH3, Srinivas, Stilzle and Schwarz found evidence for the formation of a viable neutral molecule whose fragmentation pattern and collisional activation mass spectrum were in accord with a H2C=Si structure422. These authors suggested that their experiments supported electron-capture by CH2Si+" as a mechanism for the formation of H2C=Si in interstellar space. Various models have predicted that H2C=Si is one of the most abundant forms of silicon in dense interstellar clouds423. 

Such behaviour clearly contrasts with the case of 4-iodoaniIine, where protonation in a chemical ionization source occurred not only on the ring but also on the nitrogen atom . Nitrogen protonation was indicated by ion-molecule reactions with dimethyl disulphide consecutive to collisional dehalogenation (FT-ICR experiments) or by an increase in the intensity of the peak at mjz 76 following high-energy collisional activation . 

Organophosphorus Chemistry series regularly lists new mass spectra in the Physical Methods chapter . With this in mind, an approach which considers fundamental aspects of organophosphorus ions (i.e. structure and reactivity) in the gas phase has been adopted. The gas-phase structure and reactivity of ions can be probed via several different techniques, including thermochemical measurements, kinetic energy release of metastable ions, collisional activation mass spectrometry, neutralization reionization mass spectrometry and ion-molecule reactions. An example is the molecule HCP (Table 1) its ionization potentiaP, proton affinity and the IR and rotational spectroscopy of the HCP ion " have all been determined in the gas phase. Another important tool for understanding the structure and reactivity of gas phase ions is ab initio molecular orbital theory. With advances in computational hardware and software, it is now possible to carry out high-level ab initio calculations on smaller systems. Indeed, the interplay between experiment and theory has fuelled many studies ... 

Because of the importance of the biphenyl scaffold, as a structure of pharmaceutical and active therapeutic compounds, the mass spectrometric behavior of a series of 6,6-disubstituted dibenzo[r//][l,3]dioxepins 36 has been studied. The electron ionization-induced fragmentation patterns were discussed based on use of labeled compounds, accurate mass measurements, and collisionally induced dissociation experiments using an ion trap <2006JMP577>. 

---