Singlet–triplet splittings and electron affinities of selected cyanocarbenes, XCCN (X = H, F, Cl, C2H, CN): carbenes with a stable excited negative ion state

The title compounds have been investigated using the ROHF-ACPF and CAS(2,2)-ACPF method in conjunction with the aug-cc-pVTZ basis sets. All cyanocarbenes have triplet ground states except FCCN and ClCCN, which conform to the halocarbenes in having singlet ground states. The ground state electron affinities are found to be rather high, i.e., 1.972, 2.061, 2.474, 3.359, 2.301 eV for HCCN, FCCN, ClCCN, C(CN)2 and (HC2)CCN, respectively. The existence of bound excited negative ion states has been discovered for the first time within the carbenes.