Threshold photodetachment of Al-: Electron affinity and fine structure

Tunable infrared laser spectroscopy of Al-(3p2 3PJ) has yielded an improved value for the electron affinity of aluminum and experimental data on the previously unobserved fine structure of the ionic ground state. The electron affinity is determined to be 3491.0(4) cm-1 [432.83(5) meV], and the J=0-1 and J=1-2 splittings are found to be 22.7(3) and 45.7(2) cm-1, respectively. The result for the electron affinity is in substantial disagreement with a very recent experimental investigation. Our work also indicates that isoelectronic extrapolations for the ionic fine structure were accurate within uncertainties, and is in good agreement with recent calculations of the electron affinity.