Аннотация:Magnetic-susceptibility and EPR measurements are reported which provide the first unambiguous evidence for a spin-Peierls transition in a system of linear one-dimensional antiferromagnetic Heisenberg chains. The material studied is TTFCu${\mathrm{S}}_{4}$${\mathrm{C}}_{4}$${(\mathrm{C}{\mathrm{F}}_{3})}_{4}$ (TFF stands for tetrathiafulvalinium). At 12 K, the spin-lattice system undergoes a second-order phase transition to a singlet ground state.
