A forbidden singlet--triplet anticrossing in D2

Anticrossings have been observed between the v=4, N=2, G (3d) 1Σ/subg/ and v=0, N=2, r (4d)3Pi/subg/ states of D2. These anticrossings fall into two distinct sets, fairly weak and quite narrow (<15 G) anticrossings induced by spin--orbit coupling and stronger and broader (approx.100 G) anticrossings introduced by the Fermi contact hyperfine interaction. Analysis of the positions of the anticrossings has allowed an accurate determination of the levels' zero field separation, the g factors of both the singlet and the triplet, and the quadratic Zeeman parameters for both the singlet and triplet. Hyperfine structure is also observed in four of the anticrossings which provides a measure of the diagonal Fermi contact interaction in the 3Pi state. The widths of the anticrossing curves provide values for the spin--orbit and the Fermi contact perturbations between the two states