The theoretical study of PuOn+(n=1,2,3) using a density functional method s
hows that PuO+(X(6)Sigma (-)) and PuO2+ (X(5)Sigma (-), (7)Sigma (-), (9)Si
gma (-)) ions are stable and the PuO3+ ((4)Sigma (+), (6)Sigma (+)) ion is
unstable. The analytic potential energy functions of (XC-)-C-6 for PuO+ and
X(5)Sigma (-), (7)Sigma (-), (9)Sigma (-) for PuO2+ have been derived, and
their force constants and spectroscopic data have been calculated.