Laser Spectroscopy of the y${}^7$P${}_J^{\circ }$ states of Cr I

Here we report measured and calculated values of decay rates of the 3d${}^4$(${}^5$D)4s4p(${}^3$P${}^{\mathrm{o}}$)\ y${}^7$P${}_{2,3,4}^{\mathrm{o}}$ states of Cr I. The decay rates are measured using time-correlated single photon counting with roughly 1% total uncertainty. In addition, the isotope shifts for these transitions are measured by laser induced fluorescence to roughly 0.5% uncertainty. The decay rate calculations are carried out by a hybrid approach that combines configuration interaction and the linearized coupled cluster method (CI+all-order method). The measurements provide a much needed precision benchmark for testing the accuracy of the CI+all-order approach for such complicated systems with six valence electrons, allowing to significantly expand its applicability. These measurements also demonstrate operation of a cryogenic buffer gas beam source for future experiments with MgF molecules toward quantum blackbody thermometry.