Emission spectra of Cl—CC—Cl+, Br—CC—Br+ and I—CC—I+ radical cations: Ã2Πg→X2Πu band systems and the decay of the Ã2Πg states

Abstract

Electron impact excited emission spectra of the dihalogenoacetylene radical cations, X—CC—X⁺, with X = Cl, Br, I, in the gaseous phase are presented. The band systems extend in the 360–860 nm wavelength region and are identified as the òΠ_Ω,g→X²Π_Ω,u electronic transitions of the dihalogenoacetylene cations from their photoelectron spectra. The vibrational and spin-orbit fine structure details of the emission and photoelectron spectra are compared. The decay of the òΠ_Ω,g states is found to be non-exponential although the long component is two orders of magnitude weaker than the short component. Time-resolved emission spectra and ancillary experiments indicate that both the decay components are of the òΠ_Ω,g states of the dihalogenoacetylene cations.