125 research outputs found
Enantiosensitive Structure Determination by Photoelectron Scattering on Single Molecules
X-ray as well as electron diffraction are powerful tools for structure
determination of molecules. Electron diffraction methods yield
\r{A}ngstrom-resolution even when applied to large systems or systems involving
weak scatterers such as hydrogen atoms. For cases in which molecular crystals
cannot be obtained or the interaction-free molecular structure is to be
addressed, corresponding electron scattering approaches on gas-phase molecules
exist. Such studies on randomly oriented molecules, however, can only provide
information on interatomic distances, which is challenging to analyse in case
of overlapping distance parameters and they do not reveal the handedness of
chiral systems8. Here, we present a novel scheme to obtain information on the
structure, handedness and even detailed geometrical features of single
molecules in the gas phase. Using a loop-like analysis scheme employing input
from ab initio computations on the photoionization process, we are able to
deduce the three dimensional molecular structure with sensitivity to the
position individual atoms, as e.g. protons. To achieve this, we measure the
molecular frame diffraction pattern of core-shell photoelectrons in combination
with only two ionic fragments from a molecular Coulomb explosion. Our approach
is expected to be suitable for larger molecules, as well, since typical size
limitations regarding the structure determination by pure Coulomb explosion
imaging are overcome by measuring in addition the photoelectron in coincidence
with the ions. As the photoelectron interference pattern captures the molecular
structure at the instant of ionization, we anticipate our approach to allow for
tracking changes in the molecular structure on a femtosecond time scale by
applying a pump-probe scheme in the future
Strong differential photoion circular dichroism in strong-field ionization of chiral molecules
We investigate the differential ionization probability of chiral molecules in the strong-field regime as a function of the helicity of the incident light. To this end, we analyze the fourfold ionization of bromochlorofluoromethane (CHBrClF) with subsequent fragmentation into four charged fragments and different dissociation channels of the singly ionized methyloxirane. By resolving for the molecular orientation, we show that the photoion circular dichroism signal strength is increased by 2 orders of magnitude
Subcycle interference upon tunnel ionization by counter-rotating two-color fields
We report on three-dimensional (3D) electron momentum distributions from single ionization of helium by a laser pulse consisting of two counter-rotating circularly polarized fields (390 and 780 nm). A pronounced 3D low-energy structure and subcycle interferences are observed experimentally and reproduced numerically using a trajectory-based semiclassical simulation. The orientation of the low-energy structure in the polarization plane is verified by numerical simulations solving the time-dependent Schrödinger equation.This Rapid Communication was supported by the DFG
Priority Programme “Quantum Dynamics in Tailored Intense
Fields” of the German Research Foundation (Project No.
DO 604/29-1). A.H. and K.H. acknowledge support from the
German Merit Foundation. A.K. acknowledges support from
the Wilhelm and Else Heraeus Foundation
G × E interactions as a basis for toxicological uncertainty
To transfer toxicological findings from model systems, e.g. animals, to humans, standardized safety factors are applied to account for intra-species and inter-species variabilities. An alternative approach would be to measure and model the actual compound-specific uncertainties. This biological concept assumes that all observed toxicities depend not only on the exposure situation (environment = E), but also on the genetic (G) background of the model (G × E). As a quantitative discipline, toxicology needs to move beyond merely qualitative G × E concepts. Research programs are required that determine the major biological variabilities affecting toxicity and categorize their relative weights and contributions. In a complementary approach, detailed case studies need to explore the role of genetic backgrounds in the adverse effects of defined chemicals. In addition, current understanding of the selection and propagation of adverse outcome pathways (AOP) in different biological environments is very limited. To improve understanding, a particular focus is required on modulatory and counter-regulatory steps. For quantitative approaches to address uncertainties, the concept of “genetic” influence needs a more precise definition. What is usually meant by this term in the context of G × E are the protein functions encoded by the genes. Besides the gene sequence, the regulation of the gene expression and function should also be accounted for. The widened concept of past and present “gene expression” influences is summarized here as Ge. Also, the concept of “environment” needs some re-consideration in situations where exposure timing (Et) is pivotal: prolonged or repeated exposure to the insult (chemical, physical, life style) affects Ge This implies that it changes the model system. The interaction of Ge with Et might be denoted as Ge × Et We provide here general explanations and specific examples for this concept and show how it could be applied in the context of New Approach Methodologies (NAM)
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