Ionization Energy of Cl2O and ClO, Appearance Energy of ClO+(Cl2O), and Heat of Formation of Cl2O

Abstract

The photoionization efficiency (PIE) spectrum of Cl2O was measured over the wavelength range λ = 98−117 nm by using a discharge flow−photoionization mass spectrometer apparatus coupled to a synchrotron radiation source. A value of 10.909 ± 0.016 eV was obtained for the adiabatic ionization energy (IE) of Cl2O from analysis of the photoionization 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 λ = 105−117 nm. Analysis of the photoionization threshold yields a value of IE of ClO(X2Π3/2) = 10.885 ± 0.016 eV. The appearance energy (AE) of ClO+ (from the dissociative ionization of Cl2O) was determined from the PIE spectrum of ClO+ over the wavelength range λ = 98−104 nm. Combining the AE298 value, 12.296 ± 0.032 eV, with known thermodynamic quantities yields a value for ΔfH°298(Cl2O) = 77.2 ± 3.4 kJ mol-1. From the value for ΔfH°298(Cl2O) and the equilibrium constant for the reaction Cl2O + H2O ↔ 2HOCl, a value for ΔfH°298(HOCl) = −76.8 ± 3.5 kJ mol-1 is obtained. These results for IE(Cl2O), IE(ClO), AE298(ClO+, Cl2O), ΔfH°298(Cl2O), and ΔfH°298(HOCl) are compared with previous estimates or measurements.