The magnetic circular dichroism (MCD) and absorption spectra of lutetium bis(phthalocyanine) (LuPc(2)) are reported in an argon matrix at similar to 7 K over the range 5 000-60 000 cm(-1). The better spectral resolution of the species isolated in an argon matrix, combined with determination of excited-state symmetries by MCD, permits an assignment of the main electronic transitions. The experimental data are compared with the valence effective Hamiltonian calculations of Orti et al. and the localized orbital calculations of Ishikawa et al. The spectra support the view that LuPc(2) is a delocalized mixed-valence system.