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The quantum needle of the avian magnetic compass

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Fig. 2.
Fig. 2.

Reaction yields of various radical pairs. (A) <mml:math><mml:mrow><mml:msub><mml:mi mathvariant="normal">Φ</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:msub></mml:mrow></mml:math>ΦS for a [FAD•− TrpH•+] radical pair in which the transverse principal components of selected nitrogen hyperfine interactions (Axx and Ayy) were set to zero: for N5 (blue), N10 (red), and both N5 and N10 (green). <mml:math><mml:mrow><mml:msub><mml:mi mathvariant="normal">Φ</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:msub></mml:mrow></mml:math>ΦS for the unmodified [FAD•− TrpH•+] is shown in black. In all cases, τ = 1 ms. For clarity, three of the traces have been offset vertically by 0.006 (green) and 0.003 (blue and red). (B) <mml:math><mml:mrow><mml:msub><mml:mi mathvariant="normal">Φ</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:msub></mml:mrow></mml:math>ΦS for a [FAD•− Y•] radical pair in which radical Y• contains a single 14N nucleus with an axial hyperfine tensor with principal components (Axx, Ayy, Azz) = (0.0, 0.0, 1.0812) mT (modeled on N1 in TrpH•+). The radical pair lifetimes are as indicated (1–100 μs). The angle between the z axes of Y• and FAD•− was 45°; the intensity of the spike was found to decrease smoothly to zero as this angle was increased from 0° to 90°. For clarity, the five traces for τ < 100 μs have been offset vertically, from top to bottom, by 0.020, 0.016, 0.012, 0.008, and 0.004 respectively. (C) <mml:math><mml:mrow><mml:msub><mml:mi mathvariant="normal">Φ</mml:mi><mml:mi mathvariant="normal">S</mml:mi></mml:msub></mml:mrow></mml:math>ΦS for toy radical pairs, [X• Y•]. For the red, orange and green traces, X• contains a single 14N hyperfine tensor with principal components (Axx, Ayy, Azz) = (−0.0989, −0.0989, 1.7569) mT. For the blue and black traces, (Axx, Ayy, Azz) = (−0.2, −0.2, 1.7569) and (−0.4, −0.4, 1.7569) mT, respectively. In all five cases, Y• contains a single 14N nucleus with an axial hyperfine interaction: (Axx, Ayy, Azz) = (0.0, 0.0, 1.0812) mT. The two hyperfine tensors have parallel z axes. The radical pair lifetimes are as indicated (10, 33.3, 100 μs); ×2 and ×4 indicate the doubling and quadrupling of Axx and Ayy in X•. For clarity, three of the traces have been offset vertically by 0.03 (green) and 0.06 (orange and red).

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