Direct observation of the Yb(4f136s2)F states and accurate determination of the YbF ionization energy

YbF has been identified as a molecule that can be used to investigate charge-parity symmetry violations that are beyond the standard model of particle physics. Cooling to sub-milli-Kelvin is advantageous for experiments that probe manifestations of these symmetry violations. One approach involves laser cooling of YbF via the A(2)Pi(1/2)-X-2 Sigma(+) transition. However, it appears that cooling by means of this transition may be limited by the radiative loss of population from the cooling cycle. YbF has low-energy states that arise from the Yb+(4f(13)6s(2))F- that radiative decay from A(2)Pi(1/2) to the 4f(13)6s(2) states occurs with a branching fraction of approximately 10(-3). In the present study we have used dispersed laser induced fluorescence spectroscopy to observe the lowest energy 4f(13)6s(2) states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. An accurate ionization energy (IE) of 48 703 +/- 5 cm(-1) for YbF is also reported. A two-color photoionization technique was used to determine the IE and observe the v(+) = 0-3 vibrational levels of YbF+ X-1 Sigma(+).

Automated summary

YbF is a molecule that can be used to study charge-parity symmetry violations beyond the standard model. Cooling it to sub-milli-Kelvin temperatures is advantageous for studying these violations. In this study, the lowest energy states of YbF were observed using laser-induced fluorescence spectroscopy, and the accurate ionization energy of YbF was determined using a two-color photoionization technique.