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31 P NMR spectroscopy and the study of nuclear spin singlet relaxation phenomena are of interest in particular due to the importance of phosphorus-containing compounds in physiology. We report the generation and measurement of relaxation of 31 P singlet order in a chemically equivalent but magnetically inequivalent case. Nuclear magnetic resonance singlet state lifetimes of 31 P pairs have heretofore not been reported. Couplings between 1 H and 31 P nuclei lead to magnetic inequivalence and serve as a mechanism of singlet state population conversion within this molecule. We show that in this molecule singlet relaxation occurs at a rate significantly faster than spin–lattice relaxation, and that anticorrelated chemical shift anisotropy can account for this observation. Calculations of this mechanism, with the help of molecular dynamics simulations and ab initio calculations, provide excellent agreement with the experimental findings. This study could provide guidance for the study of 31 P singlets within other compounds, including biomolecules.
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This content will become publicly available on July 10, 2026
High-Resolution Infrared Spectroscopy and Nuclear Spin Conversion of CH 3 D in Solid Parahydrogen: Crystal Field Effects in Nuclear Spin Conversion
The nuclear spin conversion of CH3D isolated in solid parahydrogen (pH2) was investigated by high-resolution Fourier transform infrared (FTIR) spectroscopy. From the analysis of the temporal changes in the CH3D/pH2 rovibrational absorption spectra, the nuclear spin conversion rates associated with rotational relaxation from the J = 1, K = 1 state to the J = 0, K = 0 state were determined over the 1.5−4.3 K temperature range. As-deposited CH3D/pH2 samples contain two different crystal structures allowing the CH3D nuclear spin conversion rates to be measured for two different trapping sites, which revealed that CH3D trapped in hexagonal closepacked (hcp) crystal sites relax more than twice as fast as CH3D isolated in face centered cubic (fcc) crystal sites. The nuclear spin conversion rates of CH3D trapped in single substitution hcp crystal sites increase rapidly above 2.5 K, but the rates were almost temperature independent below 2 K leading to a limiting nonzero conversion rate of k = 2.76(8) × 10−3 min−1 at 1.58(1) K. Comparison of the temperature dependence of the CH3D nuclear spin conversion rate measured here with analogous measurements for CH4 and CD4 trapped in solid pH2 shows that CH3D relaxes with a rate constant intermediate between CH4 and CD4, and the faster relaxation for species containing deuterium atoms can be qualitatively explained by the quadrupole interaction that is absent in all hydrogen containing CH4 isotopomers.
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- Award ID(s):
- 2101719
- PAR ID:
- 10623708
- Publisher / Repository:
- pubs.acs.org/JPCA
- Date Published:
- Journal Name:
- The Journal of Physical Chemistry A
- Volume:
- 129
- Issue:
- 27
- ISSN:
- 1089-5639
- Page Range / eLocation ID:
- 5953 to 5972
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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