Thermal Decomposition of NH2OH and Subsequent Reactions: Ab Initio Transition State Theory and Reflected Shock Tube Experiments
S. J. Klippenstein, L. B. Harding, B. Ruscic, R. Sivaramakrishnan, N. K. Srinivasan, M.-C. Su, and J. V. Michael
Chemical Sciences and Engineering Division, Argonne National Laboratory, Argonne, Illinois 60439, United States
J. Phys. Chem. A
113(38), 10241�10259 (2009)
Primary and secondary reactions involved in the thermal decomposition of NH2OH are studied with a
combination of shock tube experiments and transition state theory based theoretical kinetics. This coupled
theory and experiment study demonstrates the utility of NH2OH as a high temperature source of
OH radicals. The reflected shock technique is employed in the determination of OH radical time profiles via
multipass electronic absorption spectrometry. O atoms are searched for with atomic resonance absorption
spectrometry. The experiments provide a direct measurement of the rate coefficient, k1,
for the thermal decomposition of NH2OH.
Secondary rate measurements are obtained for the NH2 + OH (5a)
and NH2OH + OH (6a) abstraction reactions. The experimental data are obtained for temperatures
in the range from 1355 to 1889 K and are well represented by the respective rate expressions:
log[k/(cm3/molecule/s)] = (-10.12 � 0.20) + (-6793 � 317 K/T) (k1);
log[k/(cm3/molecule/s)] = (-10.00 � 0.06) + (-879 � 101 K/T) (k5a);
log[k/(cm3/molecule/s)] = (-9.75 � 0.08) + (-1248 � 123 K/T) (k6a).
Theoretical predictions are made for these rate coefficients as well for the reactions of
NH2OH + NH2, NH2OH + NH, NH + OH, NH2 + NH2,
NH2 + NH, and NH + NH, each of which could be of secondary importance in NH2OH thermal decomposition.
The theoretical analyses employ a combination of ab initio transition state theory and master equation
simulations. Comparisons between theory and experiment are made where possible.
Modest adjustments of predicted barrier heights (i.e., by 2 kcal/mol or less) generally yield good
agreement between theory and experiment. The rate coefficients obtained here should be of utility in modeling NOx
in various combustion environments.