Ultrafast control of the LnF⁺/LnO⁺ ratio from Ln(hfac)₃

The photo-induced dissociative ionization of lanthanide complexes Ln(hfac)₃ (Ln = Pr, Er, Yb) is studied using ultrafast shaped laser pulses in a time-of-flight (TOF) mass spectrometry setup. Various fluorine and Ln-containing mass fragments were observed, which can be interpreted by the photo-fragmentation mechanistic pathway involving C-C bond rotation processes proposed previously. A set of experiments used pulse shaping guided by closed-loop feedback control to identify pulses that optimize the ratio of LnF⁺/LnO⁺. In agreement with previous studies in which very little LnO⁺ was observed, broad pulses were found to maximize the LnF⁺/LnO⁺ ratio, which involves metal-ligand bond-breaking followed by bond rotation and bond rearrangement. In contrast, a transform limited (TL) pulse favored the formation of LnO⁺. Finally, the recently developed experimental control pulse slicing (CPS) technique was applied to elucidate the dynamics induced by fields that either maximize or minimize the LnF⁺/LnO⁺ ratio, which also indicates that longer laser pulses facilitate LnF⁺ formation during the C-C bond rotation dissociative-ionization process.