Laser photo-detachment

First, let s note that experimentally the EA stands as a wild quantity being mostly indirect measured, for instance trough the Haber-Bom cycle and only recently improved since the advent of the laser photo-detachment experiments with negative ions (Hotop Lineberger, 1985) and by the electron transmission spectroscopy (Jordan Burrow, 1987). 

Absorption of UV or visible light from a flash lamp or a laser is used to produce the solvated electron, too. Two photolytic processes may occur (1) the photon energy is sufficient to ionize a solute and produce the electron, for instance, photo-detachment from an anion (Cl , Fe(CN)g , Na ...) (2) the laser intensity is high enough to induce ionization of the solvent via multiphoton absorption (e.g. HjO -I- hv 112 + e ). For water, at least 8 eV is needed to ionize the solvent. 

In photodetachment studies we need not be concerned with the coulombic interaction that dominates the neutralization channel in MPI at times <10 ° s, but since the threshold for ionization of an anion is higher in the liquid than in the gas phase, we obtain once again information on the polarization energy of the ion in the liquid prior to photo-detachment. The laser photodetachment mechanism has been used with inorganic ions, such as Fe(CN)g or organic ions such as phenolate, supported in a wide range of aqueous or organic liquids. 

The photo-detachment probability might depend on the polarization state of the laser. Detachment with linear polarized lasers can lead to interference effects between electrons ejected into different directions but collected again by the electric extraction field. This effect differs for circular polarization. 

With this technique the photo-detachment spectrum of NO ions has been measured [493]. Here the laser beam is reflected by a gold mirror into the anti-collinear direction of the ion beam (Fig. 4.36). The assembly is located in an electrode arrangement of three electrodes creating an electric field that bumps the ion packet over the mirror and returns it to the incident beam axis. 

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