Photoionization mass spectrometry of NH2OH: Heats of formation of HNO+ and NOH+

Energy-dependent mass spectra are presented for the most prominent ions produced upon photoionization of hydroxylamine. Two distinct thresholds are oberved for mass 31, which we attribute to onsets for formation of HNO+ and NOH+. The corresponding heats of formation are ΔH°f,0 (HNO+) = 256.8±1.4 kcal/mol and ΔH°f,0 (NOH+) = 274.8±0.7 kcal/mol. The thresholds for mass 32, which we tentatively ascribe to H2NO+, corresponds to 224.6±0.2 kcal/mol for its heat of formation. Each of these entities can therefore be produced in an exothermic reaction of H+3 with NO, and represent mechanisms for depleting NO in the interstellar clouds. Experimental breakdown diagrams are generated and compared with predictions of QET. It is found necessary to invoke a three-body decomposition to explain some observations at higher energy. A theory is presented to accommodate this process within the framework of QET.