Abstract: The extended Solomon equations are used to describe the ¹³C spin-lattice relaxation with the ¹H RF field irradia tion. It is shown that the ¹³C spin-lattice relaxation with the ^{1H RF field irradiation is generally a triple-exponential course, which can be reduced to a single-exponential course in the absence of the 1H initial magne tization and with strong enough RF field irradiation. Based on the numerical cal culation, the large difference between the spin-lattice relaxation curves obeyi ngTC₁H}₁ and those obeying TC ₁>TH₁ is indicated. The methyl ¹³C resonance in L-valine in the solid state is examined, whose experimental results agree well with the theoretical ones.

Key words: NMR, spin-lattice relaxation, RF field, Solomon equations