A method of false coincidence removal from measurements of quadruple coincidences between two photoelectrons and two photoions generated in molecular double photoionization

Abstract

The removal of false coincidences from measurements of coincidences between two photoelectrons and one or two ions formed in molecular double photoionization is described. False coincidences arise by several mechanisms; experimental procedures and mathematical formulae required to remove all the different false coincidence contributions are described. Sample spectra taken of the double photoionization of carbon dioxide are presented to illustrate the method of false coincidence subtraction.

Strong-field-induced bond rearrangement in triatomic molecules

“…Since we are operating in the regime of ∼1 ion per laser pulse, we have a significant contribution from false coincidences, that is, coincident ions that arise from the fragmentation of two or more molecules in the same laser pulse. To reduce their effect on the the calculated branching ratio, we generate the false coincident ion pairs by randomly pairing ions from different laser pulses [2,[59][60][61]. Since we can generate an arbitrary number of random ion-pairs, we identify a purely random feature in any spectrum and generate enough false coincidences to match it, so it is properly subtracted.…”

Structure and fragmentation dynamics of N22+ions in double photoionization experiments

“…Figure 8 shows typical TPEsPICO coincidence spectra for selected electronic and vibrational levels. They were accumulated during typically 5 h in order to reach good statistics, and were treated to remove random coincidences in the way presented by Slattery et al [34]. The extraction electrode was set at 300 V. Figure 8 (spectrum (a)) shows almost exclusive detection of the parent ion N 2+ 2 .…”

A modified magnetic bottle electron spectrometer for the detection of multiply charged ions in coincidence with all correlated electrons: decay pathways to Xe3+ above xenon-4d ionization threshold

“…Although an estimation of ''pure'' random coincidences is possible (roughly, by raising to the power n the 1D signal and scaling it), it can be tedious. [38][39][40] Subtracting these random coincidences from an n-dimension data set (n-dimension matrix with sparse events) is not straightforward and relies on an algorithm to handle (multidimensional) ''images''. Often, these random coincidences appear in regions of n-dimensional space that do not overlap with the n-ionization signal due to the energy difference between the different n-ionization levels.…”