Chapter 9 Multiple Choice Questions

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. Calculate the Larmor frequency for a proton in a magnetic field of 1 T.

23.56 GHz correct incorrect

42.58 MHz correct incorrect

74.34 kHz correct incorrect

13.93 MHz correct incorrect

145.32 MHz correct incorrect

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. The Larmor frequency of an unknown nucleus detected in a Q-band hyperfine measurement (at B_res = 1.205 T) was 7.8764 MHz. Identify the unknown nucleus.

¹³C correct incorrect

¹⁴N correct incorrect

²H correct incorrect

¹⁷O correct incorrect

³¹P correct incorrect

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. Calculate the strength of the B₂ field resulting in a 90° pulse length of 5 μs for a proton.

1.174 x 10^-4 T correct incorrect

0.1174 x 10^-3 T correct incorrect

117. 4 mT correct incorrect

1 mT correct incorrect

1.174 x 10^-3 T correct incorrect

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. Calculate the frequencies of the two ENDOR transitions shown in Fig. 9.2(d) for a ¹⁵N nucleus given a = 10 MHz, assuming the spectrum was recorded on an X-band spectrometer (0.35 T).

ν_N1 = 3.489 MHz; ν_N2 = 6.511 MHz correct incorrect

ν_N1 = 12.231 MHz; ν_N2 = 22.231 MHz correct incorrect

ν_N1 = 35.679 MHz; ν_N2 = 37.190 MHz correct incorrect

ν_N1 = 73.952 MHz; ν_N2 = 83.952 MHz correct incorrect

ν_N1 = 123.753 MHz; ν_N2 = 134.864 MHz correct incorrect

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. Calculate the pulse duration time required for a 90° and 180° flip angle for an electron in a MW field of 10 mT.

6.123 ns for 90°; 22.4 ns for 180°. correct incorrect

2.396 ns for 90°; 14.4 ns for 180°. correct incorrect

8.159 ns for 90°; 8.32 ns for 180°. correct incorrect

16.543 ns for 90°; 3.9 ns for 180°. correct incorrect

8.925 ns for 90°; 17.8 ns for 180°. correct incorrect

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. Given that the Fourier transformed 3-pulse ESEEM spectrum shown in Fig. 9.9(d) was recorded at X-band frequency, identify the likely nucleus responsible for the coupling.

¹⁷O correct incorrect

¹⁵N correct incorrect

²H correct incorrect

¹H correct incorrect

¹⁴N correct incorrect

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. In a Mims-ENDOR experiment, the ENDOR efficiency can be estimated by . For values of n = 0, 1, 2,… the maximum and minimum efficiencies will occur for τ values of:

Max at τ = π/a_iso; Min at τ = 2π/a_iso correct incorrect

Max at τ = nπ/a_iso; Min at τ = π/a_iso correct incorrect

Max at τ = (2n+1)π/a_iso; Min at τ = 2nπ/a_iso correct incorrect

Max at τ = (3n+1)π/a_iso; Min at τ = (2n+)π/a_iso correct incorrect

Max at τ = π/(2n+1)a_iso; Min at τ = π/(2n)a_iso correct incorrect

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. Calculate the resonance frequencies of the two peaks expected in the Q-band ³¹P Davies ENDOR spectrum of the nucleotide guanosine-5’-diphosphate (GDP) bound to Mn^II, assuming g = g_iso = 2.007 for the Mn^II - ³¹P centre and given ^Pa_iso = 10 MHz.

ν_N1 = 52.127 MHz; ν_N2 = 62.127 MHz correct incorrect

ν_N1 = 35.703 MHz; ν_N2 = 45.703 MHz correct incorrect

ν_N1 = 9.187 MHz; ν_N2 = 15.187 MHz correct incorrect

ν_N1 = 7.316 MHz; ν_N2 = 14.316 MHz correct incorrect

ν_N1 = 15.874 MHz; ν_N2 = 25.874 MHz correct incorrect

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. An S = I = ½ two spin system in a disordered matrix with an axial hyperfine tensor produces a broad set of features in the X-band HYSCORE spectrum. Given a_iso = 4 MHz, T = 5 MHz, and I = ½ for a proton, estimate 1) the overall width of the ridges, and 2) the overall maximum curvature of the ridges for the weakly coupled system.

Width = 5 MHz; curvature = 0.1010 MHz correct incorrect

Width = 10 MHz; curvature = 0.9434 MHz correct incorrect

Width = 14 MHz; curvature = 0.4717 MHz correct incorrect

Width = 1 MHz; curvature = 1.8868 MHz correct incorrect

Width = 24 MHz; curvature = 0.2358 MHz correct incorrect

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. The EPR spectrum of a trans d¹ M(CO₄)(PPh₃)₂ complex produces an axial g tensor with g₁ = 2.045 and g_2,3 = 2.002. The ³¹P hyperfine values were found to be a_iso = 2.36 MHz and T = 0.5 MHz. Calculate the frequencies of the ³¹P ENDOR transitions at X-band when the hyperfine spectrum is recorded at the two field positions of B_res corresponding to g₁ = 2.045 and g_2,3 = 2.002.

At g₁ = 2.045 ⇒ 2.45 & 4.45 MHz; at g_2,3 = 2.002 ⇒ 3.36 & 2.36 MHz correct incorrect

At g₁ = 2.045 ⇒ 3.28 & 5.76 MHz; at g_2,3 = 2.002 ⇒ 4.36 & 5.36 MHz correct incorrect

At g₁ = 2.045 ⇒ 4.54 & 6.90 MHz; at g_2,3 = 2.002 ⇒ 4.91 & 6.77 MHz correct incorrect

At g₁ = 2.045 ⇒ 5.84 & 7.63 MHz; at g_2,3 = 2.002 ⇒ 8.71 & 9.24 MHz correct incorrect

At g₁ = 2.045 ⇒ 6.19 & 8.48 MHz; at g_2,3 = 2.002 ⇒ 5.63 & 7.63 MHz correct incorrect