Photoelectron Spectroscopy of the NCN - and HNCN - Ions
1997; American Chemical Society; Volume: 101; Issue: 24 Linguagem: Inglês
10.1021/jp964067d
ISSN1520-5215
AutoresEileen P. Clifford, Paul G. Wenthold, W. C. Lineberger, George A. Petersson, G. Barney Ellison,
Tópico(s)Mass Spectrometry Techniques and Applications
ResumoWe have used negative ion photoelectron spectroscopy to measure the electron affinities of the cyanonitrene and the cyanoamino radical: EA(X̃ 3 NCN) = 2.484 ± 0.006 eV, EA(X̃ 2A'' HNCN) = 2.622 ± 0.005 eV, and EA(X̃ 2A'' DNCN) = 2.622 ± 0.005 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: EA(X̃ 3 NCN) = 2.51 ± 0.03 eV and EA(X̃ 2A'' HNCN) = 2.60 ± 0.03 eV. Our qualitative picture of these species is NCN X̃ 3 , [NCN]- X̃ 2Πu, HNC⋮N X̃ 2A'', and [HNC⋮N]- X̃ 1A'. We make use of the electron affinities of NCN and HNCN, together with the gas phase acidity of cyanamide, ΔacidH298(H−NHCN) = 350 ± 3 kcal mol-1, to find the bond enthalpies of H2NCN. We find DH298(H−NHCN) = 96.9 ± 3.0 kcal mol-1 and ΔfH298(HNCN) = 77 ± 4 kcal mol-1, which closely agree with the calculated values: DH298(H−NHCN) = 95.5 ± 0.7 kcal mol-1 and ΔfH298(H−NCN) = 76.7 ± 0.7 kcal mol-1. We therefore use the CBS ab initio electronic structure calculations to estimate ΔacidH298(H−NCN) ≅ 339 kcal mol-1. Use of the experimental electron affinity, EA(NCN), leads to the NH bond enthalpy of the cyanoamino radical, DH298(H−NCN) = 83 ± 2 kcal mol-1 and ΔfH298(NCN) = 108 ± 4 kcal mol-1.
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