Proton tunneling in a hydrogen bond measured by cross-relaxation field-cycling NMR

1H–19F spin–lattice relaxation spectroscopy: Proton tunnelling in the hydrogen bond studied by field-cycling NMR

“…In reference [22] we have shown how the correlation time for proton transfer may be measured directly from the magnetic field dependence of the cross relaxation rate, r.…”

“…In the cross-relaxation sequence the recovery of hI z i is governed by Eq. (5) with coefficients [22] …”

“…Using the procedures described in [22] the magnetic field dependence of the off-diagonal element of the relaxation matrix, rðBÞ, was determined from experiments using the cross-relaxation pulse sequence at T ¼ 18K. The results are presented in Fig.…”

“…This introduces new challenges into the quantitative interpretation of spin-lattice relaxation data and the determination of the proton transfer rates. In a recent paper we showed how field-cycling measurements of the cross-relaxation process linking two Zeeman systems can be used to extract accurate correlation times [22]. In this present paper we undertake a wider exploration of heteronuclear 19 F-1 H spin-lattice relaxation including both diagonal and cross-relaxation components, showing how the multiple spectral density components can be resolved from the field-dependence data.…”

“…The procedures are discussed in Ref. [22]; following polarisation of the 1 H spins, the 19 F spins are saturated and the subsequent evolution of the 1 H spins is monitored as a function of time as energy flows between the two Zeeman reservoirs. The polarisation period, s pol , and polarisation field, B pol , are chosen so that the initial 1 H polarisation is equal to its equilibrium polarisation at the recovery field B r .…”