ABSOLUTE PHOTOABSORPTION OF BRCN IN THE VALENCE SHELL AND THE BROMINE-M, CARBON-K AND NITROGEN-K SHELL REGIONS (5-450 EV)

Absolute oscillator strengths (cross sections) for photoabsorption by BrCN have been measured throughout the VUV and soft X-ray regions (5-4 51 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 osc illator strengths are compared with the very limited direct optical da ta in the literature, For the sharper (Rydberg) bands the presently de termined dipole (e,e) oscillator strengths are considerably larger ind icating that significant line saturation (bandwidth) errors are occurr ing in the previously published direct optical (Beer-Lambert law) meas urements. The first absolute measurements and inner shell photoabsorpt ion spectra are reported in the carbon K (1s), nitrogen K (1s) and bro mine M (3d, 3p and 3s) regions of BrCN. The carbon and nitrogen Is spe ctra show vibrational resolution in the respective, strongly resonance enhanced, 3 pi(pi) <-- 1s bands, The Br 3d spectrum of BrCN shows cl ear evidence of ligand field splittings in the 3d(5/2)(delta, pi and s igma) and 3d(3/2)(delta and pi) 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 functiona l theory calculations. The Br 3d(5/2,3/2), ligand field split inner sh ell ionization energies are estimated using the 5p<--Br 3d excitation energies and considerations of the (transferable) 5p Rydberg term valu es from the C 1s, N is acid valence shell spectra.