PROPERTIES OF DIAZOCARBENE [CNN] AND THE DIAZOMETHYL RADICAL [HCNN] VIA ION CHEMISTRY AND SPECTROSCOPY

We have used negative ion photoelectron spectroscopy to measure the el ectron 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 reproduce d by complete basis set (CBS) ab initio electronic structure calculati ons: EA((X) over tilde (3)Sigma(-) CNN) = 1.83 +/- 0.03 eV, EA((X) ove r tilde(2)A '' HCNN) = 1.69 +/- 0.03 eV. We make use of the electron a ffinities of CNN and HCNN, together with the gas phase acidity of diaz omethane, Delta(acid)H(298)(HCHN2) = 372.2 +/- 2.1 kcal mol(-1) (CBS c alculated 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 tra nsform mass spectrometer and a tandem flowing afterglow-selected ion f low tube (FA-SIFT), we find Delta(acid)H(298)(HCNN) = 352 +/- 4 kcal m ol(-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-CN N) = 79 +/- 4 kcal mol(-1) which is in excellent agreement with the CB S-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).