SPECTROSCOPY OF THE LOW-ENERGY STATES OF BaO+

The BaO$^{+}$ cation is a promising candidate for studies conducted at ultra-cold temperatures. It is known that the ion can be formed by the reaction of laser-cooled Ba$^{+}$ with N$_{2}$O or O$_{2}$. Spectroscopic data are now needed for the BaO$^{+}$ cation, for both characterization of the internal state population distributions and the design of population transfer schemes. We have obtained the first spectroscopic data for BaO$^{+}$ using the pulsed-field ionization, zero kinetic energy (PFI-ZEKE) photoelectron technique. Two-color ionization was carried out via the A$^{1}$$Sigma$$^{+}$-X$^{1}$$Sigma$$^{+}$ transition of BaO. Vibronic levels of the X$^{2}$$Sigma$$^{+}$, A$^{2}$$Pi$$_{3/2}$ and A$^{2}$$Pi$$_{1/2}$ states of BaO$^{+}$ have been characterized. The results are compared with the predictions of high-level electronic structure calculations