Physical property determination of a particle or classification of the particle as a function of the physical property by evaluating scattered light profile from a single particle is disclosed. The particle may include chemical structures that vibrate as a function of a physical property of the particle. The physical property may include an absorptive property of the particle or a chemical composition. From a detected scattered light spectrum, at least two anomalous dispersive regions may be identified. The physical property of the particle may be determined as a function of the at least two regions. A system employing the physical property determination can achieve sensitivities useful for low particle density applications such as detection for biological and chemical agents.