Infrared Bands of Slightly Asymmetric Molecules

As an aid in the interpretation of the infrared spectra of nearly linear, slightly asymmetric molecules, calculations have been made upon molecular models of varying degrees of asymmetry in order to determine the general characteristics of their infrared bands. $A_x$, $A_y$, and $A_z$ have been chosen as the principal moments of inertia and the atoms comprising the molecule have been taken to be coplanar such that $A_x=A_y+A_z$. For convenience of calculation, a parameter $\rho$ has been chosen where $\rho =\frac{A_z}{A_y}$ and calculations have been made for ten values of $\rho$, varying in steps of $\Delta \rho =0.02\mathrm{}$ from $\rho =0.20\mathrm{}$ to $\rho =0.00\mathrm{}$. In the computation of the intensities of lines, Boltzmann factors were used corresponding to a largest moment of inertia $A_x=2.0\mathrm{}\times {10}^{-39\mathrm{}}$ gm · ${\mathrm{cm}}^2$. As in the work of Dennison on completely asymmetric molecules, of which this is essentially an extension, charts have been prepared depicting the general characteristics of the three types of bands which may occur.