Photodissociation spectroscopy of the cyanogen halides in the vacuum ultraviolet

Abstract

A systematic study of the vacuum u.v. spectroscopy of ICN, BrCN and ClCN has been conducted based on measurements of the absorption spectrum, the photofragment excitation specrum of CN(B²Σ⁺), its relative quantum yield and the polarization of the CN(B→X) fluorescence emission as a function of wavelength in the range 120–180 nm. The results establish (1) that the B and C states are associated with perpendicular transisions into the ³II, (, ½)₁ and ¹II, (½, ½)₁ components of the Rydberg states 2π→nsσ; (2) the important contributions made by an underlying continuum associated with a linear O⁺ or bent A′ upper state; (3) the presence of an intravalence transition in ClCN analogous to the ([graphic omitted]¹A′â†� [graphic omitted]) band system in HCN, which was previously unrecognised; (4) the assignment of a number of Rydberg states associated with the ²II, ²II_½ and ²Π_½ states of the ionic core and (5) the influence of (Ω_c, ω) coupling in complicating the spectroscopy of the heaviest of the cyanogen halides, ICN.