The kinetics of isomerization of deuterium and hydrogen oxoperoxonitra
te, ONOOD and ONOOH, respectively, to trioxonitrate(1-), NO3-, and a d
euteron or proton have been studied. Analysis of the pH-rate profiles
result in a normal equilibrium isotope effect (K-H/K-D) of 3.3. The ki
netic deuterium isotope effect for the isomerization reaction is 1.6 /- 0.2 between 5 and 55 degrees. The activation enthalpies of isomeriz
ation of ONOOD and ONOOH are identical within the error of the measure
ment, 86.2 +/- 0.5 and 86.5 +/- 0.5 kJ mol(-1), respectively. A second
ary kinetic isotope effect of 1.6 is compatible with a mechanism of is
omerization where the terminal peroxide O-atom shifts to the N-atom.