Direct observation of the Yb(4f13 6s2)F states and accurate determination of the YbF ionization energy

TL;DR

This study uses laser spectroscopy to observe low-energy states of YbF, crucial for laser cooling and precision measurements, and accurately determines its ionization energy, advancing molecular physics and fundamental symmetry research.

Contribution

It reports the first observation of the YbF 4f136s2 states and provides a precise measurement of the YbF ionization energy, aiding future experimental and theoretical work.

Findings

Observed YbF 4f136s2 states using laser-induced fluorescence.

Measured the ionization energy of YbF with high accuracy.

Identified vibrational levels of YbF+ for the first time.

Abstract

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 A2P1/2-X2S+ 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+(4f136s2)F- configuration. Recent theoretical calculations predict (Zhang et al J. Mol. Spectrsc. 386 11625 (2022)) that radiative decay from A2{\Pi}1/2 to the 4f136s2 states occurs with a branching fraction of approximately 10-3. In the present study we have used dispersed laser induced fluorescence spectroscopy to the observe the lowest energy 4f136s2 states. These measurements were carried out using excitation of previously unobserved YbF transitions in the near UV spectral range. An accurate ionization energy (IE) 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+ X1S+.