BROADBAND FREQUENCY COMB AND CW-LASER VELOCITY MODULATION SPECTROSCOPY OF ThF+

An experimental search for the permanent electric dipole moment of the electron (eEDM) is currently being performed using the metastable $^3Delta_1$ state in trapped HfF$^+$ $^($footnote{H. Loh, K. C. Cossel, M. C. Grau, K.-K. Ni, E. R. Meyer, J. L. Bohn, J. Ye, E. A. Cornell, Science textbf{342}, 1220 (2013).}$^)$. The use of ThF$^+$ could significantly increase the sensitivity due to the larger effective electric field and longer $^3Delta_1$ state lifetime. Previous work by the Heaven group has identified several low-lying ThF$^+$ electronic statesfootnote{B. J. Barker, I. O. Antonov, M. C. Heaven, K. A. Peterson, J. Chem. Phys. textbf{136}, 104305 (2012).}; however, the ground state could not be conclusively assigned. In addition, transitions to intermediate electronic states have not been identified, but they are necessary for state detection, manipulation, and readout in an eEDM experiment. To date we have acquired 3700 wn of densely-sampled ThF$^+$ spectra in the 695 � 1020 nm region with frequency combfootnote{L. C. Sinclair, K. C. Cossel, T. Coffey, J. Ye, E. A. Cornell, PRL textbf{107}, 093002 (2011).} and cw-laser velocity modulation spectroscopyfootnote{K.C. Cossel textit{et. al.}, Chem. Phys. Lett. textbf{546}, 1 (2012).}. With high resolution, we have accurately fit more than 20 ThF$^+$ vibronic transitions, including electronic states spaced by the known X-a energy separation$^b$. We will report on the ThF$^+$ ground state assignment and its implications for an eEDM experiment