Hyperfine rate coefficients of NH (top) out of the (n₁ = 4, j₁ = 5, F₁ = 5.5, F = 6.5) level and ND (bottom) out of the (n₁ = 4, j₁ = 5, F₁ = 5, F = 6) level at 50 K as a function of the variation in the rotational angular momentum n₁. The solid lines stand for para-H₂ collisions and the dashed lines for ortho-H₂ collisions. The ΔF₁ = ΔF − 2 and Δn₁ = Δ j₁ − 2 transitions are represented by triangles, whereas the ΔF₁ = ΔF − 1 and Δn₁ = Δ j₁ − 1 transitions are represented by squares.