We use (1+1$$) resonance-enhanced multiphoton photodissociation (REMPD) to detect the population in individual rovibronic states of trapped HfF$^+$ with a single-shot absolute efficiency of 18%, which is over 200 times better than that obtained with fluorescence detection. The first photon excites a specific rotational level to an intermediate vibronic band at 35,000-36,500 cm$^{-1}$, and the second photon, at 37,594 cm$^{-1}$ (266 nm), dissociates HfF$^+$ into Hf$^+$ and F. Mass-resolved time-of-flight ion detection then yields the number of state-selectively dissociated ions. Using this method, we observe rotational-state heating of trapped HfF$^+$ ions from collisions with neutral Ar atoms. Furthermore, we measure the lifetime of the $^3Delta_1$ $v=0,, J=1$ state to be 2.1(2) s. This state will be used for a search for a permanent electric dipole moment of the electron.
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