Effects of N15 on the Nuclear Quadrupole Resonance of N14 in Solid N2

Solid nitrogen, which consists of 99.6% N14 (I=1) at natural abundance has previously been observed to exhibit a single, strong pure quadrupole resonance line in the α phase below 35.5°K. This has been discussed by Scott in the first of this series of papers. When the sample is enriched with N15 (I=½) the N14 resonance is split into two distinct lines. For an approximately equal isotopic mixture, the splitting is 8.2 kc at 4.2°K and decreases with increasing temperature. Using the Bayer—Kushida theory as a basis, the two resonance frequencies may be attributed to the presence of two types of molecules N14–N14 and N14–N15. The former molecule has a resonance frequency close to that of pure N214 whereas the latter molecule, being heavier and thus vibrating with a smaller amplitude, has the higher frequency. The data are discussed on the basis of present theoretical and experimental understanding.