Far infrared absorption spectra of solid iodine in the region 40-150 cm(-1) have been measured up to about 10 GPa, in a diamond anvil cell. The pressure evolution of the frequency position and intensity of the two B-1u and B-2u lattice modes of the Cmca iodine crystal has been measured for the first time. The much slower increase with pressure of the experimental B-1u frequency, comparing with the calculated one, is caused, analogously to the similar behavior of the A(g) Raman libron, by the gradual molecular dissociation. The increase with pressure of the intensity of the modes can be correlated to the charge delocalization, preceding the insulator-metal transition. (C) 2003 Elsevier B.V. All rights reserved.