Collisional activation spectroscopy

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 ... 

Full equilibration of ions at a known temperature in IMS allows measuring temperature-dependent rate constants for structural transitions, from which accurate activation energies and preexponential factors could be determined in an assumption-free manner using Arrhenius plots. In contrast, structural characterization techniques implemented in vacuum, such as various laser spectroscopies (threshold photoionization,photodissociation,or photoelectron spectroscopy ), MS/MS by collisional or other dissociation, or chemical reactivity studies lack a direct ion thermometer. In those methods, ion temperature is estimated as the source temperature (possibly with semiempirical adjustments) or gauged using various indirect thermometers, and vibrationally or electronically hot ions are the ever-... 

Our studies of the effect of velocity-changing collisions in an rf-laser double resonance experiment contribute to a new vista into the role of collisictis in laser spectroscopy of sub-level structures the limitation of the observation time of the active atoms due to narrow-bandwidth optical excitation and simultaneous velocity diffusion can be of importance for a variety of spectroscopic techniques that use a velocity-selective excitation and detection of either sublevel populations or sublevel coherence. On the other hand, the collisional velocity diffusion of sublevel coherence within an optical Doppler distribution can also give rise to new and surprising phenomena as will discussed in the next section. 

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