Photoexcitation of mass/charge selected hemin⁺, caught in helium nanodroplets

We report on a method by which mass/charge selected ions are picked up from a linear ion trap by liquid helium droplets. The size distributions of the doped droplets are measured via acceleration experiments. Depending on the source temperature, droplet sizes ranging from tens of thousands to several million helium atoms are obtained. Droplets doped with hemin, an iron containing porphyrin molecule, in the charge state +1 are then investigated using laser spectroscopy. It is observed that excitation with UV/VIS light can lead to ejection of the ion from the droplet. For doped droplets with a median size of B150 000 helium atoms, the absorption of two photons at 380 nm is needed for ejection to become efficient. When droplets become smaller, the ejection efficiency is observed to strongly increase. Monitoring the ejection yield as a function of excitation wavelength can be used to obtain the optical spectrum of hemin⁺. Compared to the spectrum of free gas-phase hemin⁺ at room temperature, the narrower and shifted to the blue

Ionization of 1D and 3D oriented asymmetric top molecules by intense circularly polarized femtosecond laser pulses

We present a combined experimental and theoretical study on strong-field ionization of a three-dimensionally oriented asymmetric top molecule, benzonitrile (C$_7$H$_5$N), by circularly polarized, nonresonant femtosecond laser pulses. Prior to the interaction with the strong field, the molecules are quantum-state selected using a deflector, and 3-dimensionally (3D) aligned and oriented adiabatically using an elliptically polarized laser pulse in combination with a static electric field. A characteristic splitting in the molecular frame photoelectron momentum distribution reveals the position of the nodal planes of the molecular orbitals from which ionization occurs. The experimental results are supported by a theoretical tunneling model that includes and quantifies the splitting in the momentum distribution. The focus of the present article is to understand strong-field ionization from 3D-oriented asymmetric top molecules, in particular the suppression of electron emission in nodal planes of molecular orbitals. In the preceding article [Dimitrovski et al., Phys. Rev. A 83, 023405 (2011)] the focus is to understand the strong-field ionization of one-dimensionally-oriented polar molecules, in particular asymmetries in the emission direction of the photoelectrons.Comment: 12 pages, 9 figure

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

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

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

Reduction of quartz to silicon monoxide by methane-hydrogen mixtures

The reduction of quartz was studied isothermally in a fluidized bed reactor using continuously flowing methane-hydrogen gas mixture in the temperature range from 1623 K to 1773 K (1350 °C to 1500 °C). The CO content in the off-gas was measured online using an infrared gas analyzer. The main phases of the reduced samples identified by XRD analysis were quartz and cristobalite. Significant weight loss in the reduction process indicated that the reduction products were SiO and CO. Reduction of SiO2 to SiO by methane starts with adsorption and dissociation of CH4 on the silica surface. The high carbon activity in the CH4-H2 gas mixture provided a strongly reducing condition. At 1623 K (1350 °C), the reduction was very slow. The rate and extent of reduction increased with the increasing temperature to 1723 K (1450 °C). A further increase in temperature to 1773 K (1500 °C) resulted in a decrease in the rate and extent of reduction. An increase in the gas flow rate from 0.4 to 0.8 NL/min and an increase in the methane content in the CH4-H2 gas mixture from 0 to 5 vol pct facilitated the reduction. Methane content in the gas mixture should be maintained at less than 5 vol pct in order to suppress methane cracking

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

Manipulation of large neutral molecules with electric fields

Contains fulltext : 74867.pdf (publisher's version ) (Open Access)RU Radboud Universiteit Nijmegen, 12 februari 2010158 p