  Aims. Infrared (IR) spectroscopy is a powerful tool to study molecules in
space. A key issue in such analyses is understanding the effect that
temperature and anharmonicity have on different vibrational bands, and thus
interpreting the IR spectra for molecules under various conditions.
  Methods. We combined second order vibrational perturbation theory and the
Wang-Landau random walk technique to produce accurate IR spectra of highly
excited PAHs. We fully incorporated anharmonic effects, such as resonances,
overtones, combination bands, and temperature effects.
  Results. The results are validated against experimental results for the
pyrene molecule (C16H10). In terms of positions, widths, and relative
intensities of the vibrational bands, our calculated spectra are in excellent
agreement with gas-phase experimental data.
