Absolute photoabsorption of BrCN in the valence shell and the bromine M, carbon K and nitrogen K shell regions (5–450 eV)

Abstract

Absolute oscillator strengths (cross sections) for photoabsorption by BrCN have been measured throughout the VUV and soft X-ray regions (5–451 eV) using dipole (e,e) spectroscopy at both high (0.05–0.10 eV fwhm) and low (1 eV fwhm) resolution. Measurement of the valence shell oscillator strengths are compared with the very limited direct optical data in the literature. For the sharper (Rydberg) bands and the presently determined dipole (e,e) oscillator strengths are considerably larger indicating that significant line saturation (bandwidth) errors are occurring in the previously published direct optical (Beer-Lambert law) measurements. The first absolute measurements and inner shell photoabsorption spectra are reported in the carbon K (1s), nitrogen K (1s) and bromine M (3d, 3p and 3s) regions of BrCN. The carbon and nitrogen 1s spectra show vibrational resolution in the respective, strongly resonance enhanced, 3π(π∗) ← 1s bands. The Br 3d spectrum of BrCN shows clear evidence of ligand field splittings in the 3d52(δ, π and gS) and 3d32(δ and π) excitations to the 5p Rydberg states. The first estimates of the inner shell ionization potentials for the C 1s and N 1s core orbitals of BrCN are obtained from density functional theory calculations. The Br 3d52,32, ligand field inner shell ionization energies are estimated using the 5p←Br 3d excitation energies and considerations of the (transferable) 5p Rydberg term values from the C 1s, N 1s and valence shell spectra.