The photoion yield curves of HOBr+ and Br+ from HOBr are presented. The adiabatic I.P. of HOBr is found to be 10.638+/-0.003 eV. Autoionizing structure in HOBr+ is tentatively assigned and leads to an adiabatic I.P. of the first excited (A L(2) A’) State of similar to 11.46 eV. The 0 K threshold of Br+ from HOBr (13.915+/-0.018 eV) implies D-0(HO-Br)less than or equal to 2.101+/-0.018 eV=48.45+/-0.42 kcal/mol. Together with auxiliary thermochemicsty, this value yields Delta H-f298(0) (HOBr) greater than or equal to -13.43+/-0.42 kcal/mol, in excellent agreement with a recent ab initio value -14.2+/-1.6 kcal/mol. The resulting proton affinity of BrO is 163.8 kcal/mol. Trends observed in the properties of OX and HOX (X=F, Cl, Pr) are utilized to infer new values for Delta H-f(0)(OI) and Delta H-f(0) (HOI). Predictions are made for I.P.(HOI). Proton affinities of OX are seen to increase with heavier X, while the X (2)A"-A (2)A’ Splitting decreases.