0.0 0.1 0.2 0.3 0 10 20 30 40 Barrier  h eight ( µ K) Dipole moment (Debye) (A) (C) m$_{L}$ = 0 m$_{L}$ = ±1 (B) E V$_{1}$ V$_{0}$ FIG. 2: p -wave centrifugal barrier for dipolar collisions between fermionic polar molecules. ( A ) Schematic picture of the effective intermolecular potential for fermionic molecules at zero electric field. At intermediate intermolecular separation (center of plot), two colliding molecules are re- pelled by a large centrifugal barrier for p -wave collisions. (B) Schematic picture of the effective intermolecular potential for a relatively small applied electric field. The dipolar interactions are spatially anisotropic, with an attraction that reduces the barrier for head-to-tail collisions and a repulsion that increases the barrier for side-by-side collisions. (C) Height of the p -wave barrier as a function of dipole moment for repulsive dipole-dipole interactions ( V$_{1}$ , solid red line) and for at- tractive dipole-dipole interactions ( V$_{0}$ , dashed blue line). As the induced dipole moment increases, the spatially anisotropic dipolar interactions lower the centrifugal barrier for m$_{L}$ = 0 collisions and raise the barrier for m$_{L}$ = ± 1 collisions. The lowering of the m$_{L}$ = ± 1 barrier at very large dipole moments is due to mixing with higher partial waves, e.g. L = 3 , 5 , 7 , .... . the p -wave barrier height will be different for m$_{L}$ = 0 and m$_{L}$ = ± 1 scattering, where m$_{L}$ is the projection of the relative orbital angular momentum L onto the electric-field direction. In particular, the attractive nature of dipole-dipole interaction for polar molecules colliding “head-to-tail” lowers the barrier for m$_{L}$ = 0 collisions, while the repulsive dipole- dipole interaction for polar molecules colliding “side-by-side” raises the barrier for m$_{L}$ = ± 1 collisions. Fig. 2 A,B show these effects schematically, while Fig. 2 C shows the calculated maximum height of the m$_{L}$ = 0 and m$_{L}$ = ± 1 collisional barriers, V$_{0}$ and V$_{1}$ , respectively, as a function of d . 6