On long-lived HCCH− states

In view of the recent mass spectroscopic observations of long-lived N2− and CO− species, the lifetimes of excited states of the isoelectronic acetylene anion are investigated. The electronic structure of promising states as well as the associated decay channels are discussed and numerical results obtained at highly correlated levels of theory are given. Two doublet states are found to be stable to autodetachment via one-electron processes and for one of them the lifetimes with respect to two-electron Auger-like as well as to radiative decay are estimated. Our findings are compared to those for N2− and CO− and the relevance to the observation of a trans-bent HCCH− ion in a matrix environment is briefly discussed.