Metastability of gold-carbonyl cluster complexes, Au_N(CO)^-_M

Smaller gold-cluster anions, typified by Au^-₇, adsorb multiple CO molecules in a high-pressure, room-temperature flow-reactor, tending toward previously unknown saturation compositions, Au₇(CO)^-₄. The weakness of the gold-carbonyl adsorption bond is evidenced indirectly by the high CO partial pressure required and more directly by the high probability of fragmentation in the field-free flight region of the reflectron-type time-of-flight mass spectrometer. The analysis of this metastability reveals that the actual distribution f_N,M of products Au₇(CO)^-_M in the reactor may be highly non-statistical, e.g. with only even-M species present.