You will be shown an abstract from a biomedical research paper. Given this abstract, your task is to extract all unique entities of the following types: ["Chemical"].

Please return the output as a JSON object of the format: {"Chemical": ["Arsenic", ...]}. The keys should be entity types and values should be lists of extracted entities belonging to the corresponding type. If you cannot find entities belonging to a specific type, the value should be [].

Only output the JSON object and do not include any additional text.

Abstract:

Photoelectron and electron momentum spectroscopy of tetrahydrofuran from a molecular dynamical perspective. The results of experimental studies of the valence electronic structure of tetrahydrofuran employing He I photoelectron spectroscopy as well as Electron Momentum Spectroscopy (EMS) have been reinterpreted on the basis of Molecular Dynamical simulations employing the classical MM3 force field and large-scale quantum mechanical simulations employing Born-Oppenheimer Molecular Dynamics in conjunction with the dispersion corrected ωB97XD exchange-correlation functional. Analysis of the produced atomic trajectories demonstrates the importance of thermal deviations from the lowest energy path for pseudorotation, in the form of considerable variations of the ring-puckering amplitude. These deviations are found to have a significant influence on several outer-valence electron momentum distributions, as well as on the He I photoelectron spectrum.
{"Chemical": ["tetrahydrofuran", "He"]}