Calculation of Absolute Raman Intensities of A1 Modes of Molecules and Ions from a Delta-Function Potential Model

A delta‐function potential model of molecular binding is used to derive an expression for α_∥b, the parallel component of the molecular polarizability from the region of a chemical bond, and $\mathrm{\partial ᾱ/\partial r}$ , the derivative of the mean molecular polarizability with respect to a change in a bond length for the A₁ stretching modes of diatomic and polyatomic molecules and ions. The final expression is $\mathrm{\partial ᾱ/\partial r=}\frac{2}{3}{\mathrm{(g\sigma /Za}}_0)\frac{1}{2}{\mathrm{nr}}^3$ , in which g is the delta‐function strength; Z, the effective nuclear charge; σ, the Pauling covalent bond character; a₀, the Bohr radius; n, the number of electrons in the bond region; and r is the equilibrium internuclear distance. There is shown to be good agreement between calculated and experimental values of both α_∥b and $\mathrm{\partial ᾱ/\partial r}$ .