Resonant Laser Ablation Mass Spectrometry of Barium Compounds: Enhanced Ionization at the 455.4 nm Ba + Absorption

Tunable pulsed laser ablation mass spectra were obtained for barium‐containing solids, BaTiO 3 , Ba‐2Lu‐4Ti‐ x O, and BaF 2 , for λ=450–475 nm with target irradiances of ⪅10 6 –10 8  W cm −2 . Ablated positive ions identified by time‐of‐flight mass spectrometry included Ba 2+ , F + , O + and Ti + , each of which exhibited an intensity maximum near λ=455.4 nm (2.72 eV), which corresponds to the Ba + transition from the 6s 2 S 1/2 ground state to the 6p 2 P 3/2 excited state. The observed resonant Ba 2+ yield enhancement suggests that some excited Ba + * acquired sufficient additional energy from the ablation plasma to further ionize (IE{Ba + →Ba 2+ }=10.00 eV). The simultaneous secondary enhancement in +1 ion yields for other elements suggests collisional energy transfer from Ba + * to atomic or molecular plume species, exciting them to more easily ionized states. Although the detailed energy transfer mechanisms are indefinite, the general observations indicate that resonantly pumping energy into Ba + heats the ablation plume with some species‐selectivity. No significant wavelength‐dependence was evident in the yields of BaX + from the gas‐phase reactions of ablated Ba + with C 14 F 24 (X=F), CCl 4 (X=Cl), Br 2 (X=Br), CH 3 I (X=I) and CH 3 OH (X=OH and OCH 3 ). These observations reflect that the radiative lifetime of Ba + * 2 P 3/2 is only 6 ns, dictating that primarily ground state Ba + encounter ambient reactants as the ablation plume expands.