PHOTOIONIZATION EFFICIENCY SPECTRUM, IONIZATION-ENERGY, AND HEAT, OF FORMATION OF BR2O

The photoionization efficiency (PIE) spectrum of Br2O was measured ove r the wavelength range lambda = 100-125 nm by using a photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. A value of 10.26(4) +/- 0.01(1) eV was obtained for the adiabatic ion ization energy of Br2O from analysis of the photoionization thresholds . Also, the appearance energy (AE) of BrO+ (from the dissociative ioni zation of Br2O) was determined from the PIE spectrum of BrO+ over the wavelength range lambda = 104-110 nm. Combining the AE(298) value, 11. 71(4) +/- 0.01(4) eV, with known thermodynamic quantities yields a val ue for Delta(f)H degrees(298)(Br2O) = 107.1 +/- 3.5 kJ mol(-1). The va lue for Delta(f)H degrees(298)(Br2O) may be related to Delta(f)H degre es(298)(HOBr) through the equilibrium constant for the reaction Br2O H2O reversible arrow 2HOBr. This leads to Delta(f)H degrees(298)(HOBr ) = -60.0 +/- 3.5 kJ mol(-1).