(A) 1Co-Bla2, 2 mW, 11 K; (B) CoCo-Bla2, 2 mW, 11 K; (C, solid line) = (B) − (A); (C, dashed line) 1Co-Bla2, 2 mW, 11 K; (D, solid line) CoCo-Bla2 × 0.5, 50 mW, 7 K; (D, dashed line) 1Co-Bla2, 50 mW, 7 K; (E) (B) - (1.7 × A); (F, solid line) CoCo-Bla2 × 0.5, 100 mW, 7 K, rapid passage; (F, dashed line) 1Co-Bla2, 100 mW, 7 K, rapid passage; (G, solid line) derivative of rapid passage spectrum of CoCo-Bla2; (G, dashed line) 1Co-Bla2, 2 mW, 11 K. Rapid passage spectra were recorded using second-derivative quadrature phase-sensitive detection. The intensities of spectra shown in A – C and E are correct relative to each other. Intensities of pairs of spectra in D, F and G are arbitrary, but within each pair the intensities are correct when the multiplication factors given are taken into account.