Statistical thermodynamics of semi-flexible chain molecules

A theoretical calculation of the energy levels, and hence absorption spectrum, of an isolated vacancy in an otherwise perfect diamond lattice has been made. The concept of a defect molecule is introduced. This enables familiar molecular orbital theory to be applied in calculating the electronic structure of the defect. The quantitative results suggest that the observed band at 2$\cdot $0 eV causing irradiated diamonds to appear blue, is due to spin and orbitally allowed electronic transitions of symmetry $^{1}$E $\rightarrow \,^{1}$T$_{2}$ in the neighbourhood of isolated neutral vacancies.