Nuclear-driven Electronic Coherences in Molecules via Ultrafast Angle-Resolved Scattering

Electronic coherences in molecules are ultrafast charge oscillations on the Molecular Frame (MF). Their direct observation and separation from electronic population dynamics is a long-standing goal. We discuss a valence shell Lab Frame (LF) scattering method for probing electronic coherences in isolated targets. MF electronic coherences lead to LF electronic anisotropies directly observable by an ultrafast angle-resolved scattering technique. The scattering probe may be based on ultrafast electron or X-ray scattering, or angle-resolved photoemission. Moment analysis of the measured LF anisotropy completely separates electronic coherences from population dynamics. Our proof-of-concept demonstration is based on the technique of ultrafast Time-Resolved Photoelectron Angular Distributions (TRPADs). We emphasize that this general time-angle-resolved scattering anisotropy approach applies equally to attosecond/femtosecond electronic coherences in isolated systems.