熱烈祝賀武漢磁共振中心成立 ！ Congratulations to the Founding of Wuhan Magnetic Resonance Center!

1. 熱烈祝賀武漢磁共振中心成立！Congratulations to the Founding of Wuhan Magnetic Resonance Center!

2. The Validity of High Temperature Approximation in NMR Spectroscopy and Its Related ProblemsShangwu Ding, Cheng Lung Chen, Chin Hsin Chou丁尚武，陳正隆，周金興Department of Chemistry, National Sun Yat-Sen University中山大學化學系

3. Contents • Review of Multiple Spin Echoes • How to Remove Possible Dipolar Couplings in Liquids • Control Experiment: CRAZED(Water at RT and Boiling Water) • COSY Spectra (Water at RT and Boiling Water) • Conclusions • Acknowledgments

4. “Unusual”Multiple Spin Echos t1 t2 F2 F1

5. The CRAZED Spectrum t2 t1 τ1 nτ1 n=2: F2 F1

6. Multiple Quantum Coherence InterpretationSQC only Also MQCs

7. Multiple Quantum Coherence Interpretation SinceThe number of coupled spins, N, has to be big! But the molecular tumbling removes the couplings.“Quantum” Solution: Distant spins are dipolar coupled.

8. Demagnetization Field InterpretationBon is small! Bd

9. Summary of MQC Interpretation 1. MSE signals are caused by distant intermolecular dipolar couplings 2. High temperature approximation has to be dropped 3. Anything and everything that the MQC picture can offer can be offered by classical interpretation without above two assumptions

10. Removal of “Distant Intermolecular Dipolar Couplings” Boiling liquids Supercritical liquids Mechanical stirring Which is the easiest way? boiling water(110C) vapor exit holes

11. Control Experiments CRAZED spectra of water at room temperature vsCRAZED spectra of boiling water Expected Result: No MSE signals in F1 for boiling water no matter what gradient ratios are used if water motion is sufficiently fast. Classical Picture: Demagnetization fields are averaged out. Quantum Picture: MQCs are removed.

12. c S.Ding et al., Fig.1 b a 600 400 200 0 -200 -400 -600 Hz

13. c S. Ding et al,Fig.2 b a 600 400 200 0 -200 -400 -600 Hz

14. c S. Ding et al,Fig.2 b a 600 400 200 0 -200 -400 -600 Hz

15. c S. Ding et al,Fig.2 b a 600 400 200 0 -200 -400 -600 Hz

16. Explanation Classical:MSE Peaks Remain for Boiling Water Because Quantum:  MSE Peaks Disappear for Boiling Water Because

17. Other Arguments (time allowing) 1. Decoherence:Weakly coupled spin systems in too noisy an environment. 2. Correlation length: Spins in different molecules in liquids are too far apart to be quantum mechanically correlated. 3. Ergodicity: The number of coupled spins should not violate ergodicity. At room temperature: N ≦ the number of intra-molecular spins for liquids; N~100 for solids.

18. Conclusions At Around Room Temperature 1. No MQCs in Water (or Other Low-Viscosity Liquids) 2. Trust HTA, Please 3. “Full Quantum Treatment” Not Only Unnecessary But Also Incorrect 4. Spin Clusters Are Small, Even in Solids (<100)

19. Acknowledgments NSC NSERC CAS Thank You for Your Attention!