10min:

E. B. GORDON AND O. S. RZHEVSKY, Institute for Energy Problems of Chemical Physics (branch), 142432 Chernogolovka, Moscow Region, Russian Federation.

Along with known processes of atoms and molecules photoassociation, another process of photoassociative electron attachment, A+e+h -> A^-**-> A+e , must exist for any particle, including those without positive electron affinity; its rate constant providing laser light flux of I~ ~10⁸ W/cm² is estimated by us to amount to 10^-13cm³s^-1. The corresponding spectrum lies at energies of 10..15 eV and contains quantum state and structure information scarcely attainable theoretically.

The feasibility of developing universal technique for obtaining the short-lived negative ion spectra is discussed. It is based on the following considerations:

- since the energy of an ion state is a sum of those of a photon and an impact electron, the KrF excimer laser (h =5 eV) can be used, whereas the tuning is implemented by the electron beam energy variation in the range of \varepsilon =5..10 eV;

- since the energy of a secondary electron arising after a negative ion decay exceeds that of an impact electron by the value of h , secondary electrons could be separated easily by the methods of electron optics;

- moreover, in a number of cases the spatial distribution of secondary electron velocities correlates with the laser light polarization;

- impact electrons having the energy of several eV can penetrate into the high electron density regions of target atoms and molecules , so that the probability of photoassociative electron attachment seems to be considerable even in the case of species with negative electron affinity.