Ultrafast electron diffraction and time-resolved serial crystallography are the basis of the ongoing revolution in capturing at the atomic level of detail the structural dynamics of molecules. However, most experiments capture only the probability density of the nuclear wavepackets to determine the time-dependent molecular structures, while the full quantum state has not been accessed. Here, we introduce a framework for the preparation and ultrafast coherent diffraction from rotational wave packets of molecules, and we establish a new variant of quantum state tomography for ultrafast electron diffraction to characterize the molecular quantum states. The ability to reconstruct the density matrix, which encodes the amplitude and phase of the wavepacket, for molecules of arbitrary degrees of freedom, will enable the reconstruction of a quantum molecular movie from experimental x-ray or electron diffraction data.
Gas phase electron diffraction is a powerful technique to measure the structure of molecules in the gas phase, and time-resolved ultrafast electron diffraction has been successful in capturing structural dynamics taking place on femtosecond and picosecond time scales. Diffraction measurements, however, are not sensitive to isotope substitution, and thus cannot distinguish between isotopologues. Here we show that by impulsively aligning the molecules with a short laser pulse and observing the anisotropy in the diffraction signal over multiple revivals of the rotational wavepacket, the relative abundance of molecules with different isotopes can be determined. We demonstrate the technique experimentally and theoretically by studying the rotational dynamics of chloromethane with two naturally occurring chlorine isotopes35Cl and37Cl. We have determined the relative abundance and mass difference of the isotopes. This new methodology adds a new capability to the existing technique of ultrafast electron diffraction.
more » « less- NSF-PAR ID:
- 10366835
- Publisher / Repository:
- IOP Publishing
- Date Published:
- Journal Name:
- Journal of Physics Communications
- Volume:
- 6
- Issue:
- 5
- ISSN:
- 2399-6528
- Page Range / eLocation ID:
- Article No. 055006
- Format(s):
- Medium: X
- Sponsoring Org:
- National Science Foundation
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