  By means of vibrational spectroscopy and density functional theory (DFT), we
investigate CO adsorption on phosphorene-based systems. We find stable CO
adsorption at room temperature on both phosphorene and bulk black phosphorus.
The adsorption energy and vibrational spectrum have been calculated for several
possible configurations of the CO overlayer. We find that the vibrational
spectrum is characterized by two different C-O stretching energies. The
experimental data are in good agreement with the prediction of the DFT model
and unveil the unusual C-O vibrational band at 165-180 meV, activated by the
lateral interactions in the CO overlayer.
