The $s$-process branching at mass number $A=176$ depends on the coupling between the high-$K$ ground state and a low-lying low-$K$ isomer in ${}^{176}\mathrm{Lu}$. This coupling is based on electromagnetic transitions via intermediate states at higher energies. The properties of the lowest experimentally confirmed intermediate state at 839 keV are reviewed, and the transition rate between low-$K$ and high-$K$ states under stellar conditions is calculated on the basis of new experimental data for the 839-keV state. Properties of further candidates for intermediate states are briefly analyzed. It is found that the coupling between the high-$K$ ground state and the low-$K$ isomer in ${}^{176}\mathrm{Lu}$ is at least one order of magnitude stronger than previously assumed, leading to crucial consequences for the interpretation of the ${}^{176}\mathrm{Lu}/{}^{176}\mathrm{Hf}$ pair as an $s$-process thermometer.

• Received 20 February 2009

DOI:https://doi.org/10.1103/PhysRevC.79.045804