X-ray photoelectron spectroscopy of merocyanine dyes: Part IV. Correlation of O1 s binding energy with atomic charge calculated by Smyth's method. Application to the merocyanine 540 dye

Abstract

Smyth's equation for calculating the partial ionic character of bonds yields better results than Pauling's equation when the electronegativity difference between the bonded atoms exceeds unity. This equation is used to establish the following binding energy/partial charge correlation for the O1 s line:O1 s binding energy (eV) = 534.55 + 3.29 q. This relation is used to evaluate the conjugation of benzoxazolinic and carbonyl oxygen atoms in the MC 540 dye from the measured XPS binding energies. The partial charge on the carbonyl oxygen atoms is close to −1 and the weight of the −O-C⩽ form can be evaluated to ca. 80%.