The structural and energetic properties of the HOBr --> HBrO transition sta
te are examined using the single and doubles coupled-cluster method that in
cludes a perturbational estimate of the effect of connected triple excitati
ons [CCSD(T)]. The energy change for the isomerization reaction is best est
imated to be 56.5 kcal mol(-1) endothermic, and the activation energy for t
he process is 75.0 kcal mol(-1). (C) 1999 American Institute of Physics. [S
0021- 9606(99)31237-X].