Properties of diazocarbene [CNN] and the diazomethyl radical [HCNN] via ion chemistry and spectroscopy

Eileen P. Clifford, Paul G. Wenthold, W. Carl Lineberger, George A. Petersson, Katherine M. Broadus, Steven R. Kass, Shuji Kato, Charles H. DePuy, Veronica M. Bierbaum, G. Barney Ellison

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Abstract

We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and the diazomethyl radical: EA(X̃ 3- CNN) = 1.771 ± 0.010 eV, EA(X̃ 2A″ HCNN) = 1.685 ± 0.006 eV, and EA(X̃ 2A″ DCNN) = 1.678 ± 0.006 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: EA(X̃ 3- CNN) = 1.83 ± 0.03 eV, EA(X̃ 2A″ HCNN) = 1.69 ± 0.03 eV. We make use of the electron affinities of CNN and HCNN, together with the gas phase acidity of diazomethane, ΔacidH298(HCHN2) = 372.2 ± 2.1 kcal mol-1 (CBS calculated value = 373.4 ± 0.7), to find the bond enthalpies of H2CNN. We find DH298(H-CHN2) equal to 97 ± 2 kcal mol-1, which closely agrees with the CBS-QCI/APNO-calculated value [DH298(H-CHN2) = 98.5 ± 0.7 kcal mol-1]. From proton transfer experiments in a Fourier transform mass spectrometer and a tandem flowing afterglow-selected ion flow tube (FA-SIFT), we find ΔacidH298(HCNN) = 352 ± 4 kcal mol-1 in agreement with the CBS-QCI/ APNO-calculated value of 351.8 ± 0.7 kcal mol-1. Use of the experimental electron affinity, EA(CNN), leads to the CH bond enthalpy of the cyanoamino radical, DH298(H-CNN) = 79 ± 4 kcal mol-1 which is in excellent agreement with the CBS-QCI/APNO-calculated value: DH298(H-CNN) = 78.7 ± 0.7 kcal mol-1. If we adopt the CBS-QCI/APNO value for ΔfH298(CH2N2) [64.1 ± 0.7 kcal mol-1] as our reference, we obtain ΔfH298(HCN2) = 110 ± 2 kcal mol-1 and ΔfH298(CN2) = 136 ± 5 kcal mol-1, which are again in agreement with the CBS-QCI/APNO values: ΔfH298(HCN2) = 110.5 ± 0.7 kcal mol-1 and ΔfH298(CN2) = 138.4 ± 0.7 kcal mol-1. We recommend revised experimental values for ΔfH0(HCN) = 30.9 ± 0.7 kcal mol-1 and ΔfH298(HCN) = 30.8 ± 0.7 kcal mol-1 and find that the reaction CH (2Π) + N2 → HCN + N (4S) to be slightly endothermic, ΔrxnH0 = 1.6 ± 0.7 kcal mol-1.

Original languageEnglish (US)
Pages (from-to)7100-7112
Number of pages13
JournalJournal of Physical Chemistry A
Volume102
Issue number36
DOIs
StatePublished - Sep 3 1998

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