def nm2cm(E_nm):
    """Converts photon energy from wavelength to absolute cm-1

        Parameters
        ----------
        E_nm: float
              Photon energy in nm

        Returns
        -------
        float
             photon energy in cm-1

        Examples
        --------
        >>> nm2cm(0.04)
        0.000025
        """
    return 1 / (E_nm * 1e7)