[en] Forbidden singlet--triplet anticrossings have been observed between different M/subN/ levels of the i (3d) ³Pi/subg/, ν=1, N=6 state and the W (question) ¹Σ⁺/subg/, ν=1, N=4 state of H₂. As these anticrossings are rigorously forbidden in the absence of magnetic field mixing of rotational states, their widths are quite narrow, ranging from <10 to approx.30 G. Such narrow lines allow measurements of their center positions to approximately 3 MHz. These measurements are analyzed to yield values for the zero-field separation of the singlet and triplet levels as well as linear and quadratic Zeeman parameters. Analysis of the widths and intensities of the nine observed anticrossings yields the radiative lifetimes of the singlet and triplet states as well as the spin--orbit perturbation between them. The spin--orbit coupling between the singlet and triplet states is found to be much larger than expected from measurements of diagonal fine structure in similar triplet states