Polyatomic vibration-rotation interaction
= Polyatomic vibration-rotation interaction
{title2=$B_{\mathbf v}=B_e-\sum_i\alpha_i(v_i+d_i/2)$}
The first-order dependence of a polyatomic <rotational constant> on vibrational occupations $v_i$, where $d_i$ is the degeneracy of <normal mode> $i$. The factor $d_i/2$ accounts for all of that mode's <zero-point energy>. A single band's change in <rotational constant> generally determines one $\alpha_i$, rather than every zero-point correction needed for $B_e$.