laser ablation

Description

Microchannel Plate Detector MCP-MA25/2 sales@dmphotonics.com Featured Research: View online: http://jcp.aip.org/resource/1/jcpsa6/v138/i17/p174310_s1?isAuthorized=no&ver=pdfcov Spectroscopic observation of gold-dicarbide: Photodetachment and velocity map imaging of the AuC2 anion Photoelectron spectra following photodetachment of the gold dicarbide anion, AuC− 2 , have been recorded using the velocity map imaging technique at several excitation wavelengths. The binding energy spectra show well-defined vibrational structure which, with the aid of computational calculations and Franck-Condon simulations, was assigned to a progression in the Au--C stretching mode, ν3. The experimental data indicate that the features in the spectrum correspond to a 2A←3A transition, involving states which we calculate to have bond angles ∼147◦ but with a low barrier to linearity. EXPERIMENTAL METHOD Since the specific apparatus used for these experiments has not been previously published, a detailed description is given here. Experiments were performed under high vacuum conditions within a two chamber, differentially pumped system operated at pressures of 1 × 10^−4 and 1 × 10^−6 mbar, respectively. Gold-carbide clusters were produced within a Smalley-type laser ablation source modelled on our existing designs. The source was operated with benzene seeded in helium gas to produce the metal-carbon products. The clusters exit the source and expand towards a two stage Wiley- McLaren type time of flight where anion species are pulse extracted orthogonally into a drift region. Ion optics corrects the flight path of the extracted anions so that they enter the VMI electrodes positioned immediately after the drift region. The geometry of the time of flight electrodes was designed such that the second order space focus was coincident with the photodetachment point within the VMI electrodes.25 At this point, the ion packets of the clusters were condensed to small volumes and separated in time according to their mass to charge ratio, m/e. Individual m/e species are probed by varying the photodetachment timing. A removable (via a linear motion feed-through), dual micro-channel plate detector (MCP, Del Mar Ventures, Del Mar Photonics MCP-MA25/2) is located immediately after the VMI electrodes to provide mass spectral identification of cluster species for photodetachment. The velocity map imaging electrodes were pulsed to highvoltage 200 ns prior to the photodetachment event to ensure stable potentials. Photodetachment was performed via laser light produced by a dye laser pumped by the second harmonic of a Nd:YAG laser. The incident laser power was varied in order to keep the number of detected electrons at a rate of ∼1 per laser pulse, but was typically on the order of a few microjoules at the point of entry into the chamber. To prevent deflection of the photodetached electrons by stray magnetic fields, the detection chamber was lined with magnetic shielding (Co-Netic 0.36 mm thickness, Magnetic Shield Corp.). Research interests lay in the fields of laser chemistry and reaction dynamics, and include the following themes: Reaction Dynamics: Energy partitioning during photodissociation of van der Waals molecules. Evaporation dynamics at the liquid-vacuum interface. Electronic Spectroscopy: Structure of van der Waals clusters. 2-Dimensional Laser Induced Fluorescence (2D-LIF) spectroscopy. Rovibronic analysis of large polyatomic molecules. Nanotechnology: Nanoparticle formation using laser based methods. Molecular spectroscopy Reaction dynamics http://www.dmphotonics.com/MCP_MCPImageIntensifiers/mcpma252.htm