ISSN:
1089-7690
Source:
AIP Digital Archive
Topics:
Physics
,
Chemistry and Pharmacology
Notes:
The X˜ 1A1, a˜ 3B2, and b˜ 3A2 states of vinylidene are observed in the ultraviolet (351.1–364.0 nm) photoelectron spectra of X˜ 2B2 H2CC−, X˜ 2B2 D2CC−, and X˜ 2A' HDCC−. The X˜ 1A1 state exhibits vibrational structure well above the barrier for isomerization to acetylene. A strict lower bound to the lifetime of the singlet state against rearrangement is τ〉0.027 ps, with an estimate of τ≈0.04–0.2 ps based on a simulation of the line shapes including rotational broadening. A vibrational analysis of the singlet and lower triplet state bands provides vibrational frequencies and estimates of the changes of molecular geometries between the anion and the neutral species. A qualitative potential energy surface for the CH2 rock mode, which closely corresponds to the reaction coordinate for isomerization, is extracted from the experimental data. The adiabatic electron affinity is EA(X˜ 1A1 H2CC)=0.490±0.006 eV and the triplet term energies are T0(a˜ 3B2 H2CC)=2.065±0.006 eV and T0(b˜ 3A2 H2CC)=2.754±0.020 eV. Experimental values for the bond dissociation energy of vinyl radical, D0(H2CC–H)=80.0±5.0 kcal/mol, and the acetylene–vinylidene isomerization energy, ΔHI=46.4±5.5 kcal/mol, are derived. Combining the latter value with the upper limit of Field and co-workers, ΔHI≤44.1–44.7 kcal/mol, yields ΔHI≈41–45 kcal/mol.
Type of Medium:
Electronic Resource
URL:
http://dx.doi.org/10.1063/1.457415
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