Determination of molecular orientation at the surface of an aerosol particle by morphology-dependent photoselection.

The orientation of fluorescent molecules on the surface of an aerosol particle has been determined by using a new technique, morphology-dependent photoselection. The excitation spectrum of the angularly averaged fluorescence from a single levitated particle is measured by using an integrating sphere levitator. By utilizing the relative intensities of resonant peaks in this spectrum and knowledge of the polarization properties of different resonances, we show that the orientation of molecules relative to the surface normal may be obtained.