Ion Energy Determination

Here A and B are instrumental constants, m and q are the mass and charge of the ion and Vg is the velocity component along the drift tube axis. Thermal ions arrive at the detector in a time given by the first term, forward ions (labelled Nf ) with momentum mv, 0 (i.e. ejected initially towards the detector) arrive at an earlier time and backward ions (labelled Nb ) with mv, 0 arrive at a later time. A typical low-resolution, time-averaged TOF spectrum of N2 at the bottom of Fig. 4 shows the double-peaking that results. 

We are now faced with a problem that cannot be resolved by an improvement in resolution. We cannot state categorically whether the ions originate from the process [Nl ]-+Nb or from the process 

Frasinski et al. [15] devised a triple coincidence technique to study double ionization in the single photon regime. In these photoelectron-photoion-photoion coincidence experiments, the photoelectron provides the start pulse to an analogue-to-digital converter and the two ions the stop pulses and it was an easy matter to ensure that there was less than one molecular ion in the interaction region for the period of measurement of the ion energies, about 10 fis. In the multiphoton case, however, may ions are produced per laser pulse and this conventional approach cannot be employed. 

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Even more interesting, however, is the observation (12) that molecular dissociat ion energies determined by Equation 10, in combination with a variant of the LDA for correlation ( O), are in excellent agreement with experiment for homonuclear diatomic... 

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