Ultraviolet photoelectron spectroscopy of the tert-butylvinylidene anion

The 351 nm photoelectron spectrum of the tert-butylvinylidene anion is reported. The electron affinity of the X (1)A' state of tert-butylvinylidene is 0.645(15) eV, and the excitation energy of the (3)A' State is 1.975(15) eV. The influence of the tert-butyl substituent on the properties of the vinylidene group in the anion, neutral singlet, and neutral triplets is examined by comparing the energetics and vibrational modes apparent in the photoelectron spectrum with those of vinylidene, fluorovinylidene, and vinylvinylidene. The electronic state energetics are found to parallel closely those of unsubstituted vinylidene while the vibrational modes activated by electron detachment from the anion are similar to those of vinylvinylidene; using these findings the term energy of the (3)A'' State is estimated as 2.45(15) eV. The tert-butylvinylidene anion photoelectron spectrum is the first to be analyzed without the aid of explicit high-level ab initio calculations, due to the similarity of vibrational modes to those in the vinylvinylidene spectrum.