DOUBLY-EXCITED AUTOIONIZING STATES IN A DC FIELD - WIDTHS, POLARIZABILITIES AND HYPERPOLARIZABILITIES OF THE HE 2S(2) S-1 AND 2S2P P-3(0) STATES

We have dealt with the problem of the effect of an external DC field on the prototypical He2s2 1S and 2s2p 3P(o) (M(L) = 0, M(L) = +/-1) doubly excited autoionizing states, by computing the complex eigenvalues of appropriately constructed small non-Hermitian matrices. The major correlation effects and the mixing of autoionizing and of bound states with the open channels 1sepsilonl, 2sepsilon'l and 2pepsilon'l are taken into account to all orders. The smooth decrease of the widths as a function of field strength shows the influence of the nearby strongly coupled narrower states, 2s2p 1P(o) and 2p2 3P. The polarizabilities, alpha, and hyperpolarizabilities, gamma, are: alpha(1S) = 75.4 au, gamma(1 S) = 2.9 x 10(5) au alpha(3P(o), M(L) = 0) = 41.2 au, gamma(3P(o), M(L) = 0) = 1.2 x 10(5) au, alpha(3P(o), M(L) = +/-1) = 130.8 au, gamma(3P(o) M(L) = +/-1) = -7.0 x 10(5) au.