We study systems in which the resonance Raman process is fast due to the requirement for phonon involvement in the
absorption. The resonance enhancement is found to track the isolated molecule, or vapor phase, absorption since the
molecule does not have time to exchange energy with its neighbors. This corroborates with studies of pre-resonance,
where Heisenberg’s uncertainty principle enforces a rapid process, but differs from resonance on electronically allowed
transitions, where the resonance allows a relatively prolonged interaction. High resolution excitation spectroscopy
reveals large gains and narrow features usually associated with the isolated molecule. Vibration energies shift as the
resonance is approached and the excited state vibration levels are probed. Several multiplets and overtone modes are
enhanced along with the strongly coupled ring-breathing mode in aromatic molecules.
Identification of atmospheric aerosol species and their chemical composition may help to trace their source and better estimate their impact on climate and environment. Optical scattering of aerosols depends primarily on aerosol chemical composition, size distribution, particle shape and the wavelength used. Extraction of features due to the aerosol complex refractive index from scattering spectroscopy at a single angle of observation allows composition identification via the spectral fingerprint, as shown computationally with Mie calculations of the optical scattering. Size-dependent scattering effects are eliminated by using near-forward scattering, such as in the scattering aureole. The only features of the aerosol aureole scattering spectra that very rapidly with wavelength are associated with the composition, so the aureole can give a reliable identification of aerosol composition.