title: Photoelectron imaging of cyanovinylidene and cyanoacetylene anions.
abstract: Negative ions of cyanoacetylene and cyanovinylidene are generated simultaneously via the competing 1,1-H(2)(+) and 1,2-H(2)(+) abstraction channels of O(-) reaction with acrylonitrile. The two stable isomeric forms of the anion, CCHCN(-) and HCCCN(-), are separated by a large (approximately 2 eV) potential energy barrier. Their photodetachment provides access to both the reactant and the product sides of the neutral cyanovinylidene --> cyanoacetylene rearrangement reaction, predicted to involve only a very small barrier. Using photoelectron imaging spectroscopy at 532 and 355 nm, the adiabatic electron affinity of the reactive intermediate :C horizontal lineCHCN (X(1)A'), is determined to be 1.84 +/- 0.01 eV. The photoelectron spectrum of CCHCN(-) exhibits a vibrational progression attributed to the excitation of the CCH bending mode. The observed spectral features are reproduced reasonably well using a Franck-Condon simulation under the parallel-mode approximation. In contrast to unsubstituted acetylene, cyanoacetylene has a stable anionic state, which is adiabatically weakly bound, but has an experimentally determined vertical detachment energy of 1.04 +/- 0.05 eV. This measurement, along with the broad, structureless photoelectron spectrum of HCCCN(-) (with no identifiable origin), reflects the large geometry difference between the w-shaped structure of the anion and the linear equilibrium geometry of HCCCN.
authors.affiliation: Department of Chemistry, University of Arizona, Tucson, Arizona 85721-0041, USA.
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Goebbert
authors.forename: Dmitry
authors.initials: D
authors.lastname: Khuseynov
authors.forename: Andrei
authors.initials: A
authors.lastname: Sanov
mesh_terms: D000114:Acetylene / Q000031:analogs & derivatives* / Q000737:chemistry; D000181:Acrylonitrile / Q000737:chemistry*; D000838:Anions / Q000737:chemistry; D003198:Computer Simulation; D008956:Models, Chemical; D009570:Nitriles / Q000737:chemistry*; D056951:Photoelectron Spectroscopy; D011789:Quantum Theory; D014732:Vibration
chemical_list: D000838:Anions; D009570:Nitriles; C513097:cyanoacetylene; D000181:Acrylonitrile; D000114:Acetylene