The odd-even alternation of heteroatom-doped carbon clusters AuCn - (n ≤ 12): Experimental observations and density functional studies

A series of AuCn− clusters were generated by laser vaporization on time-of-flight mass spectrometer and the abundance of AuCn− display odd–even alternation with even-n clusters being relatively more abundant. Density functional studies at B3LYP level reveal that even-n AuCn− clusters adopt a 1Σ ground state with a linear geometry for n=2, and a 1A′ ground state with bent chain geometries for n=4, 6, 8, 10, and 12. The geometric change from linear geometry of AuC2− to bent geometry of AuCn− (n=4, 6, 8, 10, 12) is rationalized by the Mulliken–Walsh model. On the other hand, the odd-n AuCn− clusters adopt bent chain geometries in 1A′ ground states for n=3 and 5, and in 3A″ ground state for n=7, 9, and 11, as well as 3Σ ground state for n=1. This irregular stability is dependent on the energy gap between HOMO and LUMO. After combination of even-n and odd-n AuCn−, the calculated incremental energy and vertical detachment energy (VDE) demonstrate that even-n AuCn− are more stable than neighboring odd-n ones, which is in agreement with the observed odd–even alternation of the TOF signal intensities.