The benzene-Ar lowest energy triplet state T-1 intermolecular potential energy surface is evaluated using coupled cluster methods and the aug-cc-pVDZ basis set extended with a set of 3s3p2d1f1g midbond functions. This surface is characterized by an absolute minimum of -392.5 cm(-1), where the argon atom is located on the benzene C-6 axis at a distance of 3.5153 Angstrom, and has a general shape very close to the ground state S-0 and the first singlet S-1 excited state surfaces. Using the T-1 potential, the intermolecular vibrational energy levels were evaluated and the results compared to those for the ground S-0 and the excited S-1 states. The calculated fundamental frequencies for the bending and the stretching modes are lower than those in the S-1 state. The calculated data for the T-1 state is expected to have the same accuracy as previously calculated data for the S-1 state. (C) 2003 American Institute of Physics.