STABILITY OF HIGHLY EXCITED ELECTRONIC STATES OF BE-2(+)

Multireference configuration interaction calculations on about 40 elec tronic states of Be2+ are reported. The ground state X2SIGMA(u)+ (sigm a(g)2sigma(u)) is bound, with R(e) = 4.25 a0, omega(e) = 512 cm-1 and D(e) = 1.94 eV. Excited states showing a stronger bonding arise from t he excitations sigma(u) --> pi(u)(1(2)PI(u)) and sigma(g)sigma(u) --> pi(u)2(4,2SIGMA(g)-, 2SIGMA(g)+, 2DELTA(g)). Doubly excited 1(4)SIGMA( g)- has the shortest R(e) (3.43 bohr), highest omega(e) (816 cm-1) and largest D(e) (4.16 eV) so far reported for any diatomic Be species. T he existence in Be2+ of several strongly bound, doubly excited states is caused by the low energy of Be(sp) + Be+ (p) products. Most of the low-lying Rydberg members 3s, 3p and 3d of Be2+ have irregular potenti al curves (double-minima) because of avoided crossings with valence sp ecies. The Rydberg species 2(2)DELTA(g)sigma(u) --> 3ddelta(g), howeve r, has a regular potential curve. The ionization potentials and Franck -Condon factors for Be2 --> Be2+ transitions are reported. The adiabat ic ionization potentials resulting from sigma(u) --> infinity (X1SIGMA (g)+ --> X2SIGMA(u)+) appears at 7.45 eV, and shows a discrete vibrati onal structure. By contrast, ejection of a sigma(g) electron (near 11 eV) breaks the Be-Be quintets 1(5)SIGMA(u)- and 1(5)PI(g) of Be2 provi des valuable spectroscopic information about the low lying states of t he neutral and ionic species which may be difficult to obtain via opti cal spectroscopy.