Threshold photoelectron and electron-ion coincidence spectroscopies: past, present and future

The history and evolution of molecular threshold photoelectron spectroscopy and threshold photoelectron photoion coincidence spectroscopy (TPEPICO) in the gas phase over the last fifty years will be reviewed. Emphasis will be placed on instrumentation and the extraction of dynamical information about energy selected ion dissociation, not on the detailed spectroscopy of certain molecules. Three important advances have greatly expanded the power of the technique, and permitted its implementation in modern synchrotron radiation beamlines. (a) The use of velocity focusing of threshold electrons onto an imaging detector in the 1990s simultaneously improved the sensitivity and electron energy resolution, and also facilitated the subtraction of hot electron background in both threshold electron spectroscopy and TPEPICO studies. (b) The development of multi-start multi-stop collection detectors for both electrons and ions in the 2000s permitted the use of the full intensity of modern synchrotron radiation thereby greatly improving the signal-to-noise ratio. (c) Finally, recent developments involving imaging electrons in a range of energies as well as ions onto separate position-sensitive detectors has further improved the collection sensitivity, so that low density samples found in a variety of studies can be investigated. As a result, photoelectron photoion coincidence spectroscopy is now well positioned to address a range of challenging problems that include the quantitative determination of compositions of isomer mixtures, the detection and spectroscopy of free radicals produced in pyrolysis or discharge sources as well as in combustion studies.

Recent Publications:
1. Baer T, Tuckett RP (2017) Advances in Threshold Photoelectron Spectroscopy (TPES) and Threshold Photoelectron Photoion Coincidences (TPEPICO). Phys Chem Chem Phys 19:9698-9723. DOI: 10.1039/C7CP00144D
2. Tuckett RP, Harvey J, Hemberger P, Bodi A (2015) The vacuum-UV photoelectron spectroscopy of CH2F2 and CH2Cl2 revisited. J Molec Spectrosc 315:172-183. DOI: 10.1016/j.jms.2015.02.012
3. Harvey J, Tuckett RP, Bodi A (2012) A halomethane thermochemical network from imaging PEPICO experiments. J Phys Chem A 116:9696-9705. DOI: 10.1021/jp307941k
4. Harvey J, Bodi A, Tuckett RP, Sztaray B (2012) The dissociation dynamics of energy-selected fluorinated ethane cations: from time bombs on a molecular level to double-regime dissociation. Phys Chem Chem Phys 14:3935-3948. DOI: 10.1039/C2CP23878K
5. Simpson MJ, Tuckett RP (2011) Vacuum-UV negative photoion spectroscopy of gas-phase polyatomic molecules. Int Rev Phys Chem 30:197-273. DOI: 10.1080/0144235X.2011.581000