State-resolved vibrational dynamics of Ar–Kr

We report a state-resolved study of ultrafast vibrational dynamics in the singly ionized heteronuclear dimer Ar–Kr using a femtosecond pump–probe reaction microscope. A linearly polarized pump pulse initiates the dynamics by ionizing the neutral dimer and preparing a coherent superposition of vibrational states on multiple electronic potential energy surfaces of Ar–Kr⁺. A time-delayed, circularly polarized probe pulse then induces further ionization and dissociation, allowing the evolving nuclear motion to be mapped onto the time-dependent kinetic-energy-release spectra of the fragments. The resulting time- and KER-resolved measurements reveal vibrational revivals at characteristic delays, each serving as a spectroscopic signature of a specific electronic state and exhibiting agreement with numerical simulations. Fourier analysis of the delay-dependent spectra further extracts the vibrational beating frequencies, which are consistent with established spectroscopic constants.