Resonance nuclear excitation of the ${}^{229}$Th nucleus via electronic bridge process in Th~II

The 8.4 eV transition in the ${}^{229}$Th nucleus is the basis for a high-precision nuclear clock with exceptional sensitivity to new physics effects. We have identified several cases in the Th${}^{+}$ ion where electronic excitations closely resonate with the nuclear excitation, with the smallest energy difference being $\mathrm{\Delta }=-0.09$ cm${}^{-1}$. We investigate the electronic bridge process, in which nuclear excitation is induced via electronic transitions, and demonstrate that a proper selection of laser frequencies can lead to a dramatic enhancement of this effect. Additionally, we show that the interaction with electrons significantly shortens the lifetime of the nuclear excited state.