New experiments in the far infrared on the AFMR node in ferrous chloride revealed the appearance of structure of increasing complexity with rising temperature 1.3 K <T<18 K). At temperatures above 8 K we observe on the lower energy side the progressive growth of new peaks distributed in an energy band of about 10 cm−1. We propose an explanation of this structure in terms of a cluster model taking into account only nearest neighbor interactions. The observed peaks would then arise from transitions starting from thermally populated levels corresponding to different spin arrangements of the neighbors.