LETTER TO THE EDITOR Multiphoton detachment from negative ions: new theory versus experiment

Abstract. In this paper we compare the results of our adiabatic theory (Gribakin and Kuchiev 1997 Phys. Rev. A 55 3760) with other theoretical and experimental results, mostly for the halogen negative ions. The theory is based on the Keldysh approach, and shows that the multiphoton detachment rates depend only on the asymptotic parameters A and of the bound-state radial wavefunction R.r / ’ Ar−1e−r. Simple analytical expressions for the differential and total n-photon detachment cross sections are obtained. They allow us to estimate the cross sections for almost any negative ion. Our approach suggests a new physical interpretation of the nontrivial oscillatory behaviour of the differential cross sections that has been observed in experiments. It also predicts oscillations in the energy dependence of the total n-photon cross sections, due to interplay among different partial waves. In our recent work (Gribakin and Kuchiev 1997 (GK97)) a simple analytical theory of multiphoton detachment from negative ions has been developed, following the original approach of Keldysh (1964). We checked that for hydrogen our results are in agreement with accurate numerical calculations by other authors. In this paper we use our theory to calculate n-photon detachment cross sections and excess photon detachment (EPD) spectra for some negative ions that have been explored experimentally. It has been shown in GK97 that the differential cross section of n-photon detachment of an electron from a negative ion by a linearly polarized light of frequency! is (in atomic units) d .lm/n d D p