Bidentate ligation of magnesium by 1,2-dimethoxyethane in the gas phase

International audienceThe 1:1 Mg[centered ellipsis]1,2-dimethoxyethane (Mg-DXE) complexes are studied experimentally and theoretically. They are generated by a laser ablation source in a supersonic expansion. They are studied spectroscopically by resonance two-photon ionization. Density functional theory/Becke three-dimensional Lee, Yang, and Parr and ab initio calculations using the MOLPRO quantum chemistry package are performed to document their ground and excited states in a series of geometry ranging from monodentate to bidentate ligation of Mg by the O atoms of DXE. An absorption band is observed in the 27 800–30 500 cm−1 range, which, thanks to the calculations, is attributed to the bidentate complex. The structure of the band is discussed in terms of the excitation of electronic states of the complex correlating adiabatically to the 3s3p 1P and 3s4s 1S states of Mg at large separation between Mg and DXE

Femtosecond Photodissociation Dynamics of van der Waals Cationic Clusters: a tool for detecting metastable isomers of organic cations

A femtosecond pump (266 nm)–probe (800 nm) experiment as been performed on small clusters of tetrakis(dimethylamino)ethylene (TDMAE) with argon (TDMAE(Ar

Dynamics of excited tetrakis(dimethyl amino)ethylene solvated by argon atoms

The supersonic expansion of a mixture of the title molecule (TDMAE) with argon generates a beam carrying a log-normal distribution of TDAME(Ar)n clusters, broadly centered at . The femtosecond pump–probe technique is used to investigate the excited state dynamics of these clusters up to a 220 ps delay between the pump and the probe. This documents the effect of the argon environment on the TDMAE dynamics. The TDMAE molecule is excited in the valence state V within the cluster by the pump laser at 266 nm. It undergoes deformation in the excited potential energy surface that brings the initial wavepacket to a conical intersection (CI), where the electronic configuration of the molecule switches to a zwitterionic configuration Z. Compared to the behaviour of free TDMAE, the effect of the argon environment is a slow down of the wavepacket movement and an increase of the time scale of the V–Z energy transfer from 300 to 400±50 fs. This slow down effect, that we call a chistera effect, differs from a standard cage effect. Here, the deforming molecule does not experience a hard sphere collision with the argon cage, rather it pushes it away. Furthermore, umbrella oscillations of the dimethylamino groups are excited when the initial wavepacket passes the CI region. Because of the argon environment, the sharp 250 fs oscillation period of the free molecules is transformed into a broad structure of 40 fs width (FWHM) centred at about 240 fs. In addition, breathing oscillations of the argon environment with respect to the TDMAE molecule are observed with a period of 410±40 fs. Finally, long delays between the pump and the probe lasers allow us to investigate the nonradiative energy transfer from the Z electronic configuration of TDMAE(Ar)n to a charge transfer state. The effect of the evaporation of argon atoms in the neutral and the ionised clusters has been taken into account, as its time scale accompanies that of the observed phenomena

Time resolved observation of multiple electronic configurations in the electronic relaxation of isolated molecules by photoelectron imaging

Contains fulltext : 60272.pdf (preprint version ) (Open Access

Transition State Spectroscopy of the Photoinduced Ca + CH3F Reaction. 2. Experimental and Ab Initio Studies of the Free Ca***FCH3 Complex

International audienceThe Ca* + CH3F CaF* + CH3 reaction was photoinduced in 1:1 Ca***CH3F complexes formed in a supersonic expansion. The transition state of the reaction was explored by monitoring the electronically excited product, CaF, while scanning the laser that turns on the reaction. Moreover, the electronic structure of the Ca***FCH3 system was studied using ab initio methods by associating a pseudopotential description of the [Ca2+] and [F7+] cores, a core polarization operator on calcium, an extensive Gaussian basis and a treatment of the electronic problem at the CCSD(T) (ground state) and RSPT2 (excited states) level. In this contribution we present experimental results for the free complex and a comparison with the results of a previous experiment where the Ca***CH3F complexes are deposited at the surface of large argon clusters. The ab initio calculations allowed an interpretation of the experimental data in terms of two reaction mechanisms, one involving a partial charge transfer state, the other involving the excitation of the C-F stretch in the CH3F moiety prior to charge transfer

Laser Spectroscopic Studies of the E 1£+ State of the MgO Molecule

The E1Σ+ ‘Rydberg' state of 24Mg16O has been characterized by two-color resonance-enhanced two-photon ionization (R2PI) spectroscopy in the 36 000–40 000 cm−1 region. Several rotationally resolved bands, assigned consistently to 24Mg16O(E1Σ+←X1Σ+) vibronic transitions, have been analyzed. The effective Bv′(v′=0−8) constants determined exhibit an unusual variation with v′. Possible causes of this variation are discussed. Estimated spectroscopic constants for the E1Σ+ state are reported

Acute hepatitis in three patients with systemic juvenile idiopathic arthritis taking interleukin-1 receptor antagonist

<p>Abstract</p> <p>Purpose</p> <p>We investigated the etiology of acute hepatitis in three children with systemic Juvenile Idiopathic Arthritis (sJIA) taking Interleukin-1 receptor antagonist (IL1RA).</p> <p>Methods</p> <p>Laboratory and clinical data for three children with sJIA diagnosed at ages 13 months to 8 years who developed acute hepatitis during treatment with IL1RA were reviewed for evidence of sJIA flare, infection, macrophage activation syndrome (MAS), malignancy, and drug reaction.</p> <p>Results</p> <p>In all patients, hepatitis persisted despite cessation of known hepatotoxic drugs and in absence of known infectious triggers, until discontinuation of IL1RA. Liver biopsies had mixed inflammatory infiltrates with associated hepatocellular injury suggestive of an exogenous trigger. At the time of hepatitis, laboratory data and liver biopsies were not characteristic of MAS. In two patients, transaminitis resolved within one week of discontinuing IL1RA, the third improved dramatically in one month.</p> <p>Conclusions</p> <p>Although sJIA symptoms improved significantly on IL1RA, it appeared that IL1RA contributed to the development of acute hepatitis. Hepatitis possibly occurred as a result of an altered immune response to a typical childhood infection while on IL1RA. Alternatively, hepatitis could have represented an atypical presentation of MAS in patients with sJIA taking IL1RA. Further investigation is warranted to determine how anti-IL1 therapies alter immune responsiveness to exogenous triggers in patients with immune dysfunction such as sJIA. Our patients suggest that close monitoring for hepatic and other toxicities is indicated when treating with IL1RA.</p

Optimizing allocation of curricular content across the undergraduate & graduate medical education continuum

BACKGROUND: Medical educators struggle to incorporate socio-cultural topics into crowded curricula. The continuum of learning includes undergraduate and graduate medical education. Utilizing an exemplar socio-cultural topic, we studied the feasibility of achieving expert consensus among two groups of faculty (experts in medical education and experts in social determinants of health) on which aspects of the topic could be taught during undergraduate versus graduate medical education. METHODS: A modified Delphi method was used to generate expert consensus on which learning objectives of social determinants of health are best taught at each stage of medical education. Delphi respondents included experts in medical education or social determinants of health. A survey was created using nationally published criteria for social determinants of health learning objectives. Respondents were asked 1) which learning objectives were necessary for every physician (irrespective of specialty) to develop competence upon completion of medical training and 2) when the learning objective should be taught. Respondents were also asked an open-ended question on how they made the determination of when in the medical education continuum the learning objective should be taught. RESULTS: 26 out of 55 experts (13 social determinants of health and 13 education experts) responded to all 3 Delphi rounds. Experts evaluated a total of 49 learning objectives and were able to achieve consensus for at least one of the two research questions for 45 of 49 (92%) learning objectives. 50% more learning objectives reached consensus for inclusion in undergraduate (n = 21) versus graduate medical education (n = 14). CONCLUSIONS: A modified Delphi technique demonstrated that experts could identify key learning objectives of social determinants of health needed by all physicians and allocate content along the undergraduate and graduate medical education continuum. This approach could serve as a model for similar socio-cultural content. Future work should employ a qualitative approach to capture principles utilized by experts when making these decisions

Experimental and theoretical study of resonant core-hole spectroscopies of gas-phase free-base phthalocyanine

We studied N 1s−1 inner-shell processes of the free base Phthalocyanine molecule, H2Pc, in the gas-phase. This complex organic molecule contains three different nitrogen sites defined by their covalent bonds. We identify the contribution of each site in ionized, core–shell excited or relaxed electronic states by the use of different theoretical methods. In particular, we present resonant Auger spectra along with a tentative new theoretical approach based on multiconfiguration self-consistent field calculations to simulate them. These calculations may pave the road towards resonant Auger spectroscopy in complex molecules

Characterization of the I 2 ؊ anion ground state using conventional and femtosecond photoelectron spectroscopy

The X 2 ⌺ u ϩ state of the I 2 Ϫ anion has been fit to a Morse potential using data from two techniques: conventional and femtosecond photoelectron spectroscopy ͑FPES͒. Conventional photoelectron spectroscopy is used to determine the adiabatic electron affinity of I 2 as well as the well depth and equilibrium nuclear geometry of I 2 Ϫ . In the FPES experiment, the pump pulse induces coherent nuclear motion on the ground state of I 2 Ϫ by resonant impulsive stimulated Raman scattering ͑RISRS͒, and the vibrational frequency of the anion is determined from the resulting oscillatory structure in the time-dependent photoelectron spectra. We find the electron affinity ͑EA͒ of I 2 to be 2.524Ϯ0.005 eV, the well depth (D e ) for I 2 Ϫ to be 1.014Ϯ0.005 eV, the equilibrium internuclear separation (R e ) to be 3.205Ϯ0.005 Å, and the vibrational frequency to be 110Ϯ2 cm Ϫ1 . These values for the I 2 Ϫ potential parameters differ significantly from previous results