Quadratic Stark shift of a polar linear rotor
= Quadratic Stark shift of a polar linear rotor
The dipole coupling $-pE\cos\theta$ connects only $J\pm1$ at fixed $m$. For $J\ge1$, second order gives $(pE)^2[J(J+1)-3m^2]/[2BJ(J+1)(2J-1)(2J+3)]$; the ground-state result is separately $-(pE)^2/(6B)$. Here $B$ has <energy> units and $\theta$ is the <polar angle> to the field.