A study of the valence shell photoionisation yields of the cyanogen halides

Abstract

Abstract The valence shell photoionisation yields of ClCN, BrCN and ICN have been recorded between threshold and 32 eV using synchrotron radiation. The yields exhibit much new structure, some of which has been assigned to Rydberg series converging onto either the A 2 Σ + or the C 2 Σ + limit. Furthermore, in ICN two Rydberg series have been observed converging onto the Ω=1/2 component of the X 2 Π state. The ion yields of ClCN and BrCN display features due to transitions into vibronically excited levels. Hot band excitations involving the bending mode are also evident. In all three molecules the 3 σ → 6 σ intravalence transition gives rise to a broad peak with a term value of ∼3.1 eV. Some of the many unassigned features should be associated with excitations from the 1π orbital. However, the irregular nature of the structure due to this orbital has prevented firm assignments being proposed.