We report IR active N₂ stretching frequencies in isolated and size selected cobalt cluster nitrogen adsorbate complexes, [Co_n(N₂)₁]⁺ as recorded by virtue of InfraRed Photon Dissociation (IRPD) spectroscopy. The observed frequencies of the [Co_n(N₂)₁]⁺ complexes (n = 8–17) are significantly redshifted (2180 to 2290 cm⁻¹) with respect to the IR inactive vibrations of free N₂ (2359 cm⁻¹). These bands are assigned to a μ₁ head-on type of coordination of the N₂ to the cobalt cluster surface, revealing remarkable cluster size dependent features to interpret.