Emission spectra of the cations of 1,3- and 1,4-dibromotetrafluorobenzene and of 1,3,5-tribromotrifluorobenzene in the gaseous phase

A search was made for radiative decay of electronically excited cations of 24 bromobenzenes and of their fluoro-substituted derivatives in the gaseous phase. The only emission spectra detected were for the cations of 1,3- and 1,4-dibromotetrafluorobenzene and of 1,3,5-tribromotrifluorobenzene. The band systems, which are found between 670 and 830 nm, are assigned to the B(??-1) ??? A(??-1), X(??-1) electronic transitions of these cations. The assignments are based on the Ne(I) photoelectron spectra which are also presented for some of the studied species. The interpretation for the absence of detectable emission is that the nature of the B cationic states is ??-1, except in the case of 1,3- and 1,4-dibromobenzene cations for which B states are still formed by ??-1 processes. Possible reasons for these observations are discussed. The symmetries of the lowest three electronic states of the studied cations are given. ?? 1980.