Photodissociation of BrCN in the vacuum ultraviolet region

Abstract

The absolute cross sections for the production of CN(A 2Π i) and CN(BB 2Σ +) from BrCN were measured over the excitation wavelength range 105–150 nm (67000–95000 cm −1), using synchrotron radiation. The quantum yields for the CN(A) and CN(B) productions were also determined. The yields were observed to increase with the excitation energy from ≈0.02 at 145 nm to ≈0.1 at 105 nm. The production of CN(X 2Σ +) is possibly the dominant photochemical channel of BrCN in the vacuum ultraviolet (VUV) region. The fragment CN (B 2Σ +−X 2Σ +) emission was found to be partially polarized with respect to the direction of the electric vector of the incident radiation. The polarization anisotropy of the emission depends on the type of transitions relevant to photodissociation; an examination of the polarization versus excitation energy curve has provided information on the symmetry of the upper electronic states. Based on these experimental results, the assignments of the Rydberg and/or intravalence transitions of BrCN in the VUV region are discussed in connection with the photochemical properties of the high-energy electronic states. The absorption spectrum of BrCN below 105 nm is also reported.