| Popis: |
A 35Cl2H double-resonance study of deuterium in the orthorhombic solid phase of deuterium chloride has been made at temperatures below the transition to the cubic phase (105.03 K). The temperature dependence of the deuterium coupling constant was obtained over the range 4.2 to 90 K and the fine structure was resolved. Upon pulsed irradiation of the deuterium transitions, a 35Cl echo envelope modulation is observed, the period of which corresponds to the frequency of the fine structure mentioned above. This establishes the origin of the structure to be due to dipolar coupling between the two spin species, and not due to a nonaxial component in the field gradient at 2H The theory of this echo modulation is given and it leads to an echo structure EDR(2τ) = E0(2τ)[1 + 2 cos (2δτ)], where δ is the scale constant for the dipolar coupling between 35Cl and 2H. Under double irradiation, the deuterium NQR line is a doublet, and the splitting observed is 2.97 kHz (mean deviation ±0.02) from 4.2 to 77 K. This is substantially smaller than the value of 3.29 kHz calculated from the neutron diffraction bond length of 1.30 A. The discrepancy is interpreted as arising principally from the averaging of the dipolar interaction by the molecular librational motion. Since the quadrupole coupling and the dipolar interaction depend upon the librational motion through the same angular dependence, one may use the observed decrease in dipole coupling strength to estimate the rigid lattice coupling constant for 2H to be 166.8 kHz (0.2481 a.u.). If one uses instead the librational amplitudes obtained from the neutron diffraction structure, one obtains a value of 155.2 kHz (0.2310 a.u.). These values are discussed as they relate to theoretical estimates, and to measurements in the cubic solid and the liquid phases. |
