Photoelectron photoion coincidence spectroscopy
[6] The inherent compromise between resolution and collection efficiency was resolved by applying velocity map imaging[7] conditions.
The first high energy resolution PEPICO experiment at a synchrotron was the pulsed-field ionization setup at the Chemical Dynamics Beamline of the Advanced Light Source.
The electrons are extracted by a continuous electric field and are velocity map imaged depending on their initial kinetic energy.
[21] Times-of-flight of photoelectrons and photoions can be combined in a form of a map, which visualizes the dynamics of the dissociative ionization process.
[22] Ion–electron velocity vector correlation functions can be obtained in double imaging setups, in which the ion detector also delivers position information.
[23] The relatively low intensity of the ionizing VUV radiation guarantees one-photon processes, in other words only one, fixed energy photon will be responsible for photoionization.
A mass spectrum is recorded at every photon energy, and the fractional ion abundances are plotted to obtain the breakdown diagram.
The total phase space volume is calculated in a microcanonical ensemble using the known energy and the density of states of the dissociating ion.
[25] Statistical theory can also be used in the microcanonical formalism to describe the excess energy partitioning in sequential dissociation steps, as proposed by Klots[26] for a canonical ensemble.
Such a statistical approach was used for more than a hundred systems to determine accurate dissociative photoionization onsets, and derive thermochemical information from them.
[27] Furthermore, algorithms based on probabilistic Bayesian analyses are known to considerably reduce systematic biases induced by false coincidences.
The intensity of these false coincidences can big strong enough to appear as a separate peaks in the signal and complicate the analysis of the spectra.
[30] If different sample molecules produce shared fragment ions, a complete thermochemical chain can be constructed, as was shown for some methyl trihalides,[31] where the uncertainty in e.g. the CHCl2Br, (Halon-1021) heat of formation was reduced from 20 to 2 kJ mol−1.
