Off-shell length for the two-nucleon T matrix in the S13-D13 state

It is shown that the off-shell behavior of the low energy two-nucleon T matrix, in the coupled S13-D13 state, can be characterized by a single parameter, which is the generalization from central to noncentral forces of the equivalent or off-shell length. An approximate linear relation between the square of the off-shell length and the intrinsic range, which holds for central forces, is shown to be also valid for noncentral forces. It is found that the approximate relation is exact for a separable potential of the Yamaguchi type, and hence for the unitary pole approximation.