Cavity-dumping a single infrared pulse from a free-electron laser for two-color pump-probe experiments.

Electromagnetic radiation in the mid- to far-infrared spectral range represents an indispensable tool for the study of numerous types of collective excitations in solids and molecules. Short and intense pulses in this terahertz spectral range are, however, difficult to obtain. While wide wavelength-tunability is easily provided by free-electron lasers, the energies of individual pulses are relatively moderate, on the order of microjoules.

Structures and magnetic properties of small [Formula: see text] and Co Cr (n = 3-5) clusters.

Small cobalt clusters [Formula: see text] and their single chromium atom doped counterparts Co Cr (n  =  3-5) were studied mass spectrometrically by measuring the infrared multiple photon dissociation (IRMPD) spectra of the corresponding argon tagged complexes. The geometric and electronic structures of the [Formula: see text] and Co Cr (n  =  3-5) clusters as well as their Ar complexes were optimized by density functional theory (DFT) calculations. The obtained lowest energy structures were confirmed by comparing the IRMPD spectra of [Formula: see text] and [Formula: see text] (n  =  3-5, m  =  3 and 4) with the corresponding calculated IR spectra.

Direct IR Spectroscopic Detection of a Low-Lying Electronic State in a Metal Carbide Cluster.

The electronic structure of metal clusters is notoriously difficult to detect spectroscopically, due to rapid relaxation into the ground state following excitation. We have used IR multiple photon excitation to identify a low-lying electronic state in a tantalum carbide cluster. The electronic excitation is found at 458 cm , and is confirmed by experiments on isotopically labeled clusters.

Structures of the dehydrogenation products of methane activation by 5d transition metal cations revisited: Deuterium labeling and rotational contours.

A previous infrared multiple photon dissociation (IRMPD) action spectroscopy and density functional theory (DFT) study explored the structures of the [M,C,2H] products formed by dehydrogenation of methane by four, gas-phase 5d transition metal cations (M = Ta, W, Ir, and Pt). Complicating the analysis of these spectra for Ir and Pt was observation of an extra band in both spectra, not readily identified as a fundamental vibration. In an attempt to validate the assignment of these additional peaks, the present work examines the gas phase [M,C,2D] products of the same four metal ions formed by reaction with perdeuterated methane (CD).

Increased expression of miR-155 and miR-222 is associated with lymph node positive status.

Identification of prognostic molecular markers of breast cancer is extremely important. The spreading out of the primary breast tumour cells to the lymphatic system is at the forefront of symbolising the first signs of distant organ metastasis. Deregulated genes in breast cancer tissues that spread to lymph nodes may show early predictive molecular markers.

Selective C-H Bond Cleavage in Methane by Small Gold Clusters.

Methane represents the major constituent of natural gas. It is primarily used only as a source of energy by means of combustion, but could also serve as an abundant hydrocarbon feedstock for high quality chemicals. One of the major challenges in catalysis research nowadays is therefore the development of materials that selectively cleave one of the four C-H bonds of methane and thus make it amenable for further chemical conversion into valuable compounds.

Structural assignment of small cationic silver clusters by far-infrared spectroscopy and DFT calculations.

The structures of small cationic silver clusters Ag (n = 3-13) are investigated by comparing measured far-infrared multiple photon dissociation spectra of cluster-argon complexes with the calculated harmonic vibrational spectra of different low-energy structural isomers. A global structure search was carried out using the CALYPSO structure prediction method, after which isomers were locally optimized with the meta GGA functional TPSS. The obtained structures of the cationic silver clusters are mostly consistent with earlier ion mobility measurements and photodissociation spectroscopy studies for Ag (n = 3-11) and allowed excluding several structural isomers that were considered in those earlier studies, which illustrates the strength of combining multiple experimental techniques for conclusive structural identification.

Geometrical Structures of Partially Oxidized Rhodium Cluster Cations, RhO (m = 4, 5, 6), Revealed by Infrared Multiple Photon Dissociation Spectroscopy.

Infrared multiple photon dissociation (IRMPD) spectra of RhO (m = 4-10) are obtained in the 300-1000 cm spectral range using the free electron laser for infrared experiments (FELIX) via dissociation of RhO or RhO-Ar complexes. The spectra are compared with the calculated spectra of several stable geometries obtained by density functional theory (DFT) structural optimization. The spectrum for RhO shows prominent bands at 620 and 690 cm and is assigned to a capped-square pyramidal Rh atom geometry with three bridging O atoms and one O atom in a hollow site.

Determination of the geometric structure of neutral niobium carbide clusters via infrared spectroscopy.

We report experimental vibrational spectra of small neutral niobium carbide clusters in the 350-850 cm spectral range. Clusters were first irradiated by IR light and subsequently probed using UV light with photon energies just below the ionization threshold. Upon resonance with an IR vibrational mode, the number of cluster ions increases, allowing to record a vibrational spectrum.

The repopulation of electronic states upon vibrational excitation of niobium carbide clusters.

We study the infrared (IR) resonant heating of neutral niobium carbide clusters probed through ultraviolet photoionization spectroscopy. The IR excitation not only changes the photoionization spectra for the photon energies above the ionization threshold, but also modulates ion yield for energies significantly below it. An attempt to describe the experimental spectra using either Fowler's theory or thermally populated vibrational states was not successful.

Water Dissociation upon Adsorption onto Free Iron Clusters Is Size Dependent.

Cationic iron clusters, produced through laser ablation and subsequently complexed with a water molecule Fen(+)-H2O (n = 6-15) are mass-selectively investigated via infrared multiple photon dissociation (IR-MPD) spectroscopy in the 300-1700 cm(-1) spectral range. The experimental data are complemented by density functional theory calculations at the OPBE/TZP level for the Fe13(+)-H2O system. The observed spectra can be explained by a mixture of clusters where for a majority water is adsorbed molecularly but for a small but significant fraction also dissociation of water molecules occurs.