Vibrational spectra of trifluoramine, NF3, dissolved in liquid Ar were studied at 90 K in the concentration range between 2 X 10(-5) and 0.1 mole fraction, using Fourier transform spectroscopy. The concentration dependence of the band shapes in the region of the combination transitions nu(1) + nu(3), nu(2) + nu(3), and 2 nu(3) involving the strong nu(3) mode was studied and the absorption associated with NF3 dimers was isolated. This absorption is compared with spectra of NF3 dimers calculated on the basis of resonant dipole-dipole interaction between two doubly degenerate oscillators. Spectra of pure liquid NF3 were recorded for comparison. Using the nu(1) + nu(3) absorption band of the NF3 dimer the distance R between two NF3 molecules was determined to be R = 4.5(1) Angstrom in solution in liquid Ar. This distance is compared with the separation between two NF3 molecules in liquid NF3 and with the value calculated from the pair distribution function obtained from Monte Carlo simulations. (C) 2004 American Institute of Physics.