Stark deceleration of CaF molecules in strong- and weak-field seeking states

We report the Stark deceleration of CaF molecules in the strong-field seeking ground state and in a weak-field seeking component of a rotationally-excited state. We use two types of decelerator, a conventional Stark decelerator for the weak-field seekers, and an alternating gradient decelerator for the strong-field seekers, and we compare their relative merits. We also consider the application of laser cooling to increase the phase-space density of decelerated molecules.Comment: 10 pages, 8 figure

Coulomb explosion imaging of small organic molecules at LCLS.

Fragmentation of small organic molecules by intense few-femtosecond X-ray free-electron laser pulses has been studied using Coulomb explosion imaging. By measuring kinetic energies and emission angles of the ionic fragments in coincidence, we disentangle different fragmentation pathways, for certain cases can reconstruct molecular geometry at the moment of explosion, and show how it depends on LCLS pulse duration

Imaging Molecular Structure through Femtosecond Photoelectron Diffraction on Aligned and Oriented Gas-Phase Molecules

This paper gives an account of our progress towards performing femtosecond time-resolved photoelectron diffraction on gas-phase molecules in a pump-probe setup combining optical lasers and an X-ray Free-Electron Laser. We present results of two experiments aimed at measuring photoelectron angular distributions of laser-aligned 1-ethynyl-4-fluorobenzene (C8H5F) and dissociating, laseraligned 1,4-dibromobenzene (C6H4Br2) molecules and discuss them in the larger context of photoelectron diffraction on gas-phase molecules. We also show how the strong nanosecond laser pulse used for adiabatically laser-aligning the molecules influences the measured electron and ion spectra and angular distributions, and discuss how this may affect the outcome of future time-resolved photoelectron diffraction experiments.Comment: 24 pages, 10 figures, Faraday Discussions 17

MORC1 exhibits cross-species differential methylation in association with early life stress as well as genome-wide association with MDD

Early life stress (ELS) is associated with increased vulnerability for diseases in later life, including psychiatric disorders. Animal models and human studies suggest that this effect is mediated by epigenetic mechanisms. In humans, epigenetic studies to investigate the influence of ELS on psychiatric phenotypes are limited by the inaccessibility of living brain tissue. Due to the tissue-specific nature of epigenetic signatures, it is impossible to determine whether ELS induced epigenetic changes in accessible peripheral cells, for example, blood lymphocytes, reflect epigenetic changes in the brain. To overcome these limitations, we applied a cross-species approach involving: (i) the analysis of CD34+ cells from human cord blood; (ii) the examination of blood-derived CD3+ T cells of newborn and adolescent nonhuman primates (Macaca mulatta); and (iii) the investigation of the prefrontal cortex of adult rats. Several regions in MORC1 (MORC family CW-type zinc finger 1; previously known as: microrchidia (mouse) homolog) were differentially methylated in response to ELS in CD34+ cells and CD3+ T cells derived from the blood of human and monkey neonates, as well as in CD3+ T cells derived from the blood of adolescent monkeys and in the prefrontal cortex of adult rats. MORC1 is thus the first identified epigenetic marker of ELS to be present in blood cell progenitors at birth and in the brain in adulthood. Interestingly, a gene-set-based analysis of data from a genome-wide association study of major depressive disorder (MDD) revealed an association of MORC1 with MDD

17O NMR evidence for 180°-flips of (COOH)2 units in dimethylmalonic acid

A previous 1H, 2H and 13C NMR study of dimethylmalonic acid DMMA revealed an intriguing motional process in the hydrogen bonded CO*OH-[Htilde]ÕÕ*[Ctilde] units [1]. Considering just the hydrogens it consists of an exchange of H and [Htilde]. Two models, I and II, were proposed: (I) a mere exchange of H and [Htilde]; (II) a 180°-flip of the whole CO*OH-[Htilde]ÕÕ*[Ctilde] unit followed by a rapid readjustment of H and [Htilde] along the hydrogen bonds. To distinguish between the two models, we report here on 17O NMR spectra and rotation patterns recorded at -55°C, where the motion is frozen out, and at 20°C, where the exchange rate is 147 kHz, from an orientated, 17O enriched single crystal of DMMA. Apart from central transitions, a host of quadrupolar split satellites appears in the -55°C spectra. At 20°C we still observe central transitions, but virtually no satellites. By way of simulations of spectra/rotation patterns, we show that the absence of satellites in the 20°C spectra is not consistent with a mere exchange of H and [Htilde]. Model II leads, on the other hand, to such severe exchange broadening of the satellites at 20°C that they become unobservable in a real experiment. Model II is therefore consistent with our experiments and is thought to apply to DMMA. This conclusion is checked by recording spectra up to 70°C from a second crystal. As model II requires, coalesced and exchange narrowed satellites indeed reappear at elevated temperatures

Search for a magnetic-field dependence of the interaction of the nuclear quadrupole moment with the electric-field gradient

It is argued that the nuclear quadrupole–electric field gradient (EFG) interaction is, in principle, dependent on the presence of a magnetic fieldB. A rough estimate of the size of this effect yields 10−4in fields up to 10 T. However, if the site symmetry of the nucleus in question includes time-reversal symmetry, the linear dependence of the EFG onBvanishes. In diamagnetic compounds, time-reversal symmetry is violated only by the presence of nuclear spins. In such compounds, the dominant dependence of the EFG onBshould be quadratic and should be described by a fourth-rank tensor. In ferro- and antiferromagnetic compounds time-reversal symmetry is strongly violated and a linear dependence of the EFG onB, described by a third-rank tensor, is expected. A search for a magnetic field dependence of the EFG was carried out by measuring the quadrupole coupling constants (QCCs) of the27Al and14N nuclei in corundum and sodium nitroprusside (SNP) by pure NQR, and by NMR in fields of 6.3 and 11 T. These diamagnetic compounds were selected because previous measurements, done in different fields, yielded differing results for the QCCs. A new technique for measuring QCCs by NMR is introduced that circumvents the necessity of precisely orienting the sample crystals. For the QCCs of both the27Al and14N nuclei in corundum and SNP, respectively, a precision of distinctly better than 10−4is reached. The results obtained in 0, 6.3, and 11 T fields fully agree with each other which means that, in fields up to 11 T, any possible field dependence of the QCCs is smaller than 10−4. These results confirm that in diamagnetic compounds a linear dependence of QCCs onBis largely suppressed