PHOTOIONIZATION MASS-SPECTROMETRIC STUDIES OF SB2 AND BI2

The photoion yield curves of Sb2+(Sb2) and Bi2+(Bi2) are presented. In both cases, two autoionizing series (designated psigma and ppi) are o bserved, converging on the excited 2SIGMA(g)+ state. From this informa tion, the ionization energy of the 2SIGMA(g)+ state in Sb2 is lowered to 9.247 eV. The difference in quantum defects, delta(ppi)-delta(psigm a), is shown to be related to the quadrupole moment of the molecular i on core of the A2SIGMA+ state in Pn2+. The adiabatic ionization energi es (AIP) are also decreased: AIP(Sb2) less-than-or-equal-to 8.43 eV, A IP (Bi2) less than or similar to 7.34 eV. Although the uppermost occup ied orbital is nominally a bonding ppi orbital, an analysis leads to t he surprising conclusion that D0(Pn2+) greater than or similar to D0(P n2), where Pn=P, As, Sb, and Bi.