The photoionization mass spectrum of NH2, prepared by the reaction H+N2H4, is presented. The adiabatic ionization potential is 11.14±0.01 eV (0.32 eV lower than reported by PES). A prominent autoionizing Rydberg series is observed, converging to the excited Ã 1A1 state at 12.445±0.002 eV. By extrapolation, NH2 should absorb strongly at ∼1150 Å. From the threshold for formation of NH+ (NH2), we obtain ΔH0f 0(NH+)=396.3±0.3 kcal/mol. With auxiliary data, we compute ΔH0f 0(NH)=85.2±0.4 kcal/mol, ΔH0f 0(NH2)=45.8±0.3 kcal/mol, D0(H2N–H)=106.7±0.3, D0 (HN–H)=91.0±0.5, and D0 (N–H)=79.0±0.4 kcal/mol. Additional photoionization measurements on N2H4 and N2H3 are also included.

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