Ring puckering dynamics molecular models

Let X be the ring-puckering coordinate and y the PH inversion coordinate in 3-phospholene (see Fig. 33). The dynamics of isomerization in this molecule is assumed to be adequately described by these coupled two DOF s without need for consideration of other DOFs. Under this assumption, the Harthcock-Laane potential energy surface consists of a fourth-order polynomial in x, a fourth-order polynomial in y, and a sixth-order polynomial coupling x and y. With molecular rotation neglected, the model Hamiltonian for 3-phospholene is given by... 

---