Photoabsorption spectra of Hg₈ have been calculated at various cluster temperatures and external pressures. A diatomics-in-molecules method has been used to model cluster electronic structure and classical isothermal–isobaric Monte Carlo simulations have been employed for sampling representative cluster configurations. Contributions of different structural isomers of the Hg₈ cluster have been analyzed and related to structural transitions in the cluster, particularly those induced by an increased pressure.