IONIZATION-ENERGY OF CL2O AND CLO, APPEARANCE ENERGY OF CLO+ (CL2O), AND HEAT OF FORMATION OF CL2O

The photoionization efficiency (PIE) spectrum of Cl2O was measured ove r the wavelength range lambda = 98-117 nm by using a discharge flow-ph otoionization mass spectrometer apparatus coupled to a synchrotron rad iation source. A value of 10.90(9) +/- 0.01(6) eV was obtained for the adiabatic ionization energy (IE) of Cl2O from analysis of the photoio nization thresholds. The ClO radical was produced via the reaction F Cl2O --> FCl + ClO and the PIE spectrum of ClO was measured over the wavelength range lambda = 105-117 nm. Analysis of the photoionization threshold yields a value of IE of ClO(X(2) Pi(3/2)) = 10.88(5) +/- 0.0 1(6) eV. The appearance energy (AE) of ClO+ (from the dissociative ion ization of Cl2O) was determined from the PIE spectrum of ClO+ over the wavelength range lambda = 98-104 nm. Combining the AE(298) value, 12. 29(6) +/- 0.03(2) eV, with known thermodynamic quantities yields a val ue for Delta(f)H(298)(degrees)(Cl2O) = 77.2 +/- 3.4 kJ mol(-1). From t he value for Delta(f)H(298)(degrees)(Cl2O) and the equilibrium constan t for the reaction Cl2O + H2O <----> 2HOCl, a value for Delta(f)H(298) (degrees)(HOCl) = -76.8 +/- 3.5 kJ mol(-1) is obtained. These results for IE(Cl2O), IE(ClO), AE(298)(ClO+, Cl2O), Delta(f)H(298)(degrees)(Cl 2O), and Delta(f)H(298)(degrees)(HOCl) are compared with previous esti mates or measurements.