Knowledge Bank

A method for calculating the nuclear magnetic double-resonance spectra based on the general density matrix formalism of $Bloch1$ and using the notational simplification of $Redfield2$ is given. The method consists of first determining the deviation from the equilibrium spin density matrix caused by the strong irradiating radiofrequency field, in the rotating coordinate system, and then determining the effect of the weak observing field. The resulting density matrix is then used to calculate the frequencies and intensities in the double resonance $spectrum3$. This procedure has been applied to the frequency-sweep double-resonance spectra of 2-bromo, 5-chlorothiophene obtained under several conditions of irradiation. All these spectra show some pronounced resonances below the baseline. The spectra were calculated using several relaxation mechanisms and compared with the experiment.