Abstract
The conversion of light into usable chemical and mechanical energy is pivotal to several biological and chemical processes, many of which occur in solution. To understand the structure–function relationships mediating these processes, a technique with high spatial and temporal resolutions is required. Here, we report on the design and commissioning of a liquid-phase mega-electron-volt (MeV) ultrafast electron diffraction instrument for the study of structural dynamics in solution. Limitations posed by the shallow penetration depth of electrons and the resulting information loss due to multiple scattering and the technical challenge of delivering liquids to vacuum were overcome through the use of MeV electrons and a gas-accelerated thin liquid sheet jet. To demonstrate the capabilities of this instrument, the structure of water and its network were resolved up to the hydration shell with a spatial resolution of 0.6 Å; preliminary time-resolved experiments demonstrated a temporal resolution of 200 fs.
Highlights
Ultrafast solution phase photochemistry is the pillar of many biological and chemical processes, such as vision, photosynthesis, and DNA photodamage,[1,2,3] responsible for converting light into usable chemical and mechanical energy
Limitations posed by the shallow penetration depth of electrons and the resulting information loss due to multiple scattering and the technical challenge of delivering liquids to vacuum were overcome through the use of MeV electrons and a gas-accelerated thin liquid sheet jet
The shallow penetration depth of electrons compared to hard x rays had, until recently, limited their use in the study of liquid-phase samples, as excessive multiple scattering prevents the retrieval of structural information
Summary
Ultrafast solution phase photochemistry is the pillar of many biological and chemical processes, such as vision, photosynthesis, and DNA photodamage,[1,2,3] responsible for converting light into usable chemical and mechanical energy. The liquid-phase ultrafast electron diffraction (LUED) instrument presented here minimizes the loss of information due to multiple scattering through the use of mega-electron-volt (MeV) electrons and a gas-accelerated liquid sheet jet[12,15] capable of producing sample thicknesses on the order of 100 nm. In combination with the ability to achieve both sub-200 fs full width at half maximum (FWHM) temporal resolution and momentum transfer ranges in excess of 10 A À1, this makes liquid-phase MeV UED a method to probe solution phase photochemistry with the potential to resolve effects, e.g., from hydrogen bonding In this manuscript, we report on the design and commissioning of an MeV LUED instrument for optical pump-electron probe studies of liquid-phase samples, enabling the use of the MeV UED in liquid samples for the first time. IV in three parts: (A) Integration with the SLAC MeV UED beamline, (B) Sample chamber, and (C) Sample delivery
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