Electron-Ion Covariance Mapping

As the intensity rises well above 10 W/cm, a molecule such as N2 has many fragmentation pathways involving N , N and fragment ions. The measured photoelectron spectrum will be the sum of contributions from all possible processes and, since energy shifts are almost inevitable, the conventional, time-averaged photoelectron spectrum may be impossible to analyse. In order to be able to associate each photoelectron peak with a parent or fragment ion, an electron-ion correlation experiment is required. In the case of electron-ion covariance, Z(t) in Eq. (3) is now the photoelectron TOF spectrum recorded at the same time as the ion TOF spectrum, 7(t). 

M magnetic Feld coils L aspheric doublet lens system 

Since the laser is highly linearly polarised with its E vector along the drift tube axes, the electrons are ejected initially towards or away from the electron detector. The ions are also ejected preferentially towards (Hf ) or away from (Hb) the ion detector. The design of the double drift tube is such that the forward and backward electrons and forward and backward ions arrive at their respective detectors with a TOP, t, given by Eq. (1) the instrumental constants, A and B, differ for electrons and ions. Hence the electron and ion TOP spectra are symmetric about their respective zero energy TOPs. 

Pigure 9 shows an electron-ion covariance map obtained at the same time as Pig. 8b. Por convenience the time-averaged electron and ion TOP spectra are shown alongside the x and y axes. The electron TOP is virtually structureless, the slight forward-backward asymmetry and the peak at 292 ns being due to a small inhomogeneity in the extraction field. The forward electrons are unaffected and a kinetic energy scale is shown for both electrons and protons. In order to ensure that this lack of structure was not the result of poor instrumental resolution, an electron TOP spectrum of Xe was taken under identical conditions. A series of ATI peaks was observed in both the forward and backward direction, separated by about 2 eV. 

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