Long-Range Predissociation in Two-Color Photoassociation of Ultracold Na Atoms

We report two-color photoassociative ionization of sodium in a magneto-optical trap. The experimental results yield information on both singly and doubly excited states. We find that the highest bound vibrational levels ({ital v}{approx_gt}20) of the singly excited 0{sub {ital g}}{sup {minus}} state predissociate into the 3{sup 2}{ital P}{sub 3/2}+3{sup 2}{ital S}{sub 1/2}({ital F}{sub {ital g}}=1) dissociation continuum due to avoided crossings of the hyperfine components of this potential with other molecular symmetries. Based on symmetry and energy consideration we argue that a doubly excited 1{sub {ital u}} state remains autoionizing even when only a few GHz above the dissociation continuum. {copyright} {ital 1996 The American Physical Society.}