A theoretical study of the (NCO)-N-2+(OH)-O-2 reaction

Four reaction channels for the title reaction were theoretically studied at the B3LYP/6-311++G(d,p) theory level. At 298.15 K the most favorable route to HCO + NO (reaction 1) is the singlet one with an energy barrier of 15.3 kcal/mol in close agreement with the reported value of 15.0 kcal/mol. Both the singlet and the triplet pathways to yield CO + NO + H (reaction 2) are kinetically competitive with an energy barrier of 20.7 kcal/mol. The tripl et channels to HNCO + O (reaction 3) and to NCOH + O (reaction 4) present a n energy barrier at 298.15 K of 11.5 and 29.6 kcal/mol, respectively, where as those for the corresponding reverse processes are 16.2 and 5.9 kcal/mol to compare with the reported values of 11.4 and 4.0 kcal/mol, respectively. Except for reaction 2 the rate determining TSs remain the same at higher t emperatures. The tripler pathway to HNCO + O is the most favored one at the three temperatures considered in this work: 298.15, 1000, and 1500 K, At h igher temperatures reaction 4 remains the most disfavored kinetically but t he Gibbs energy barriers for reactions 1-3 become closer the higher the tem perature so that at 1500 K reactions 1 and 2 are competitive with reaction 3. These trends would agree with the increase of the concentration of NO an d the decrease of the concentration of HNCO found experimentally. It is int eresting to note that reaction 2, which has been found to be a high rate an d sensitive reaction by reaction-path analysis, is the most kinetically fav ored one by an increase of temperature.