Molecular-ion trap-depletion spectroscopy of BaCl+

We demonstrate a simple technique for molecular-ion spectroscopy. BaCl+ molecular ions are trapped in a linear Paul trap in the presence of a room-temperature He buffer gas and photodissociated by driving an electronic transition from the ground X-1 Sigma(+) state to the repulsive wall of the A(1)Pi state. The photodissociation spectrum is recorded by monitoring the induced trap loss of BaCl+ ions as a function of excitation wavelength. Accurate molecular potentials and spectroscopic constants are determined. A comparison of the theoretical photodissociation cross sections with the measurements shows excellent agreement. This study represents an important step toward the production of ultracold ground-state molecular ions.