Nuclear Quadrupole Resonance of N¹⁴ in Ethylenediamine

Abstract

The temperature dependence of the nuclear quadrupole resonance of N¹⁴ in C₂H₄(NH₂)₂ was studied between 77°K and 280°K. The resonance lines were measured with a Pound-Watkins’ type recording spectrometer by applying frequency modulation.
The curve of resonance frequency vs. temperature exhibited a break around 180°K. It could be attributed to a phase transition of the crystal structure. Another break suggesting the phase transition was also observed around the liquid nitrogen temperature.
The quadrupole coupling constant eQq and the asymmetry parameter η were 3.9965 Mc and 0.313 at the liquid nitrogen temperature. By assuming hybridized atomic orbitals of sp³ type for the nitrogen bonds, two alternative models were employed. In one model three nitrogen bonds have equal s-hybridization, and in the other model s-hybridization of the N-C bond is different from that of the N-H bonds. It was shown that the latter model was suitable.