We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and the diazomethyl radical: EA(Χ ˜3Σ -CNN) ) 1.771 ( 0.010 eV, EA(Χ ˜2A′′ HCNN) ) 1.685 ( 0.006 eV, and EA(Χ ˜2A′′ DCNN) ) 1.678 ( 0.006 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations: EA(Χ ˜3Σ -CNN) ) 1.83 ( 0.03 eV, EA(Χ ˜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, ∆ acid H 298 (HCHN 2 ) ) 372.2 ( 2.1 kcal mol -1 (CBS calculated value ) 373.4 ( 0.7), to find the bond enthalpies of H 2 CNN. We find DH 298 (H-CHN 2 ) equal to 97 ( 2 kcal mol -1 , which closely agrees with the CBS-QCI/APNO-calculated value [DH 298 (H-CHN 2 ) ) 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 ∆ acid H 298 (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, DH 298 (H-CNN) ) 79 ( 4 kcal mol -1 which is in excellent agreement with the CBS-QCI/APNO-calculated value: DH 298 (H-CNN) ) 78.7 ( 0.7 kcal mol -1 . If we adopt the CBS-QCI/APNO value for ∆ f H 298 (CH 2 N 2 ) [64.1 ( 0.7 kcal mol -1 ] as our reference, we obtain ∆ f H 298 (HCN 2 ) ) 110 ( 2 kcal mol -1 and ∆ f H 298 (CN 2 ) ) 136 ( 5 kcal mol -1 , which are again in agreement with the CBS-QCI/APNO values: ∆ f H 298 (HCN 2 ) ) 110.5 ( 0.7 kcal mol -1 and ∆ f H 298 (CN 2 ) ) 138.4 ( 0.7 kcal mol -1 . We recommend revised experimental values for ∆ f H 0 (HCN) ) 30.9 ( 0.7 kcal mol -1 and ∆ f H 298 (HCN) ) 30.8 ( 0.7 kcal mol -1 and find that the reaction CH ( 2 Π) + N 2 f HCN + N ( 4 S) to be slightly endothermic, ∆ rxn H 0 ) 1.6 ( 0.7 kcal mol -1 .

Zwitterions are critically important in many biological transformations and are used in numerous chemical processes. The consequences of electrostatic effects on reactivity and physical properties, however, are largely unknown. In this work, we report the results of negative ion photoelectron spectra of nine isomeric pyridinium dicarboxylate zwitterions and three nonzwitterionic methoxycarbonylpyridine carboxylate isomers (-O(2)CPyrCO(2)CH(3)). Information about the intramolecular electrostatic interactions was directly obtained from the photoelectron spectra. The adiabatic and vertical detachment energies were measured and understood in terms of intramolecular Coulombic forces. Calculations at the B3LYP and CCSD(T) level were performed and compared to the experimental electron binding energies. Structures, relative stabilities, and the electron detachment sites also were obtained from the calculations.