Photoelectron spectroscopy of binary-metal cluster anions containing sulfur atom

Photoelectron spectra of M_nS^-₁ (M = Al, Cu, Ag, and Au) cluster anions were measured at the photon energies of 3.49 and 4.66 eV using a magnetic-bottle electron spectrometer having ∼60-meV resolution. The electron affinities of AlS^-, CuS^-, AgS^-, and AuS^- are 2.60(3), 2.10(3), 2.09(3), and 2.44(3) eV, respectively. The large EA of AlS^- is attributed to large stability by six bonding electrons, and a new electronic state of A′²Π can be found 0.4 eV above the AlS ground state, which is in agreement with a theoretical calculation. In the photoelectron spectrum of AuS^-, two peaks due to a splitting by the L-S coupling could be observed, and the amount of the splitting is 0.18(2) eV. The results of aluminum clusters containing sulfur atom will also be presented.