Photoelectron spectroscopy of HC4N-.

We report the 364-nm photoelectron spectrum of HC(4)N(-). We observe electron photodetachment from the bent X(2)A" state of HC(4)N(-) to both the near-linear X(3)A" and the bent ã (1)A' states of neutral HC(4)N. We observe an extended, unresolved vibrational progression corresponding to X(3)A" ← X(2)A" photodetachment, and we measure the electron affinity (EA) of the X(3)A" state of HC(4)N to be 2.05(8) eV. Photodetachment to the bent ã (1)A' state results in a single intense origin peak at a binding energy of 2.809(4) eV, from which we determine the singlet-triplet splitting (ΔE(ST)) of HC(4)N: 0.76(8) eV. For comparison and to aid in the interpretation of the HC(4)N(-) spectrum, we also report the 364-nm photoelectron spectra of HCCN(-) and DCCN(-). Improved signal-to-noise over the previous HCCN(-) and DCCN(-) photoelectron spectra allows for a more precise determination of the EAs and ΔE(ST)s of HCCN and DCCN. The EAs of HCCN and DCCN are measured to be 2.001(15) eV and 1.998(15) eV, respectively; ΔE(ST)(HCCN) is 0.510(15) eV and ΔE(ST)(DCCN) is 0.508(15) eV. These results are discussed in the context of other organic carbene chains.