Light scattering and spectral inversion in a matrix-isolated molecule

Spectra, recorded in the manner of conventional absorption spectra, of polycrystalline samples of cyclohexane doped with anisole guest molecules at 10−4 M/M, exhibit a surprising behavior as a function of temperature, absorption features at high temperatures appearing inverted at low temperature. An analogous inversion is observed for spectral holes burned into these spectra. It is proposed that this unexpected phenomenon is an intriguing artifact, caused by strong elastic light scattering that attenuates the incident beam to such an extent that fluorescence and phosphorescence emission dominates the detected signal at low temperatures.