10 20 30 40 50 r$_{sc }$ [fm] -1 -0.95 -0.9 [tan δ$^{c}$ ] 2nd n=1 n=2 n=3 n=4 n=5 n=6 tan c FIG. 3: (Color on line) The two-nucleon second order estimate [tan δ$_{c}$ ] 2 nd as a function of r$_{sc}$ for different values of n . As a reference the exact value for tan δ$_{c}$ is given as a straight line. 30