We have used negative ion photoelectron spectroscopy to measure the electron affinities of diazocarbene and the diazomethyl radical : EA((X) over tilde (3)Sigma(-) CNN) = 1.771 +/- 0.010 eV, EA((X) over tilde (2)A " HCNN) = 1.685 +/- 0.006 eV, and EA((X) over tilde (2)A " DCNN) 1.678 +/- 0.006 eV. Our experimental findings are accurately reproduced by complete basis set (CBS) ab initio electronic structure calculations : EA((X) over tilde (3)Sigma(-) CNN) = 1.83 +/- 0.03 eV, EA((X) over tilde(2)A " 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, Delta(acid)H(298)(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 Delta(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, 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 Delta(f)H(298)(CH2N2) [64.1 +/- 0.7 kcal mol(-1)] as our reference, we obtain Delta(f)H(298)(HCN2) = 110 +/- 2 kcal mol(-1) and Delta(f)H(298)(CN2) = 136 +/- 5 kcal mol(-1), which are again in agreement with the CBS-QCI/APNO values : Delta(f)H(298)(HCN2) = 110.5 +/- 0.7 kcal mol(-1) and Delta(f)H(298)(CN2) 138.4 +/- 0.7 kcal mol(-1). We recommend revised experimental values for Delta(f)H(o)(HCN) = 30.9 +/- 0.7 kcal mol(-1) and Delta(f)H(298)(HCN) = 30.8 +/- 0.7 kcal mol(-1) and find that the reaction CH ((2)Pi) + N-2 --> HCN + N (S-4) to be slightly endothermic, Delta(rxn)H(o) = 1.6 +/- 0.7 kcal mol(-1).