Detecting Electron Motion in Atoms and Molecules

Ultrafast electron pulses have been proposed to observe time-dependent phenomena in atoms and molecules [1]. Detection of spatial and temporal electronic motion by scattering of sub-fs pulses of 10 keV electrons from coherent superpositions of electronic states of both H and T$_2^+$ is investigated [2]. In such pump/probe calculations for the H atom, we predict measurable changes of the diffraction images that reflect the time-dependent effective radius of the electronic charge density. For an aligned T$_2^+$ molecule, we predict diffraction image changes that reflect the time-dependent localization (de-localization) of the electronic charge density about one (two) of the nuclei.\\[4pt] [1] P.~Baum and A.H.~Zewail, Proc.~Natl.~Acad.~Sci.~U.S.A.~\textbf{104}, 18409 (2007); S.A.~Hilbert, C.~Ulterwaal, B.~Barwick, H.~Batelaan, and A.H.~Zewail, Proc.~Natl.~Acad.~Sci.~U.S.A.~\textbf{106}, 10558 (2009).\\[0pt] [2] H.-C. Shao and A.F.~Starace, Phys.~Rev.~Lett.~\textbf{105}, 263201 (2010).