Femtosecond multichannel photodissociation dynamics of CH3I from the A band by velocity map imaging

4 pages, 3 figures, 1 table.The reaction times of several well-defined channels of the C–I bond rupture of methyl iodide from the A band, which involves nonadiabatic dynamics yielding ground state I(2P3/2) and spin-orbit excited I*(2P1/2) and ground and vibrationally excited CH3 fragments, have been measured by a combination of a femtosecond laser pump-probe scheme and velocity map imaging techniques using resonant detection of ground state CH3 fragments. The reaction times found for the different channels studied are directly related with the nonadiabatic nature of this multidimensional photodissociation reaction.Two of the authors (J. G. I. and J. D.) gratefully acknowledge financial support from the FPI program and the CSIC-Unidades Asociadas program, respectively, of the Spanish Ministry of Education and Science (MEC). This work has been financed by the Spanish MEC through Grant No. CTQ2005-08493- C02-01.Peer reviewe

A femtosecond velocity map imaging study on B-band predissociation in CH 3I. II. the 2 0 1 and 3 0 1 vibronic levels

Femtosecond time-resolved velocity map imaging experiments are reported on several vibronic levels of the second absorption band (B-band) of CH 3I, including vibrational excitation in the 2 and 3 modes of the bound 3R 1(E) Rydberg state. Specific predissociation lifetimes have been determined for the 201 and 301 vibronic levels from measurements of time-resolved I*( 2P 12) and CH 3 fragment images, parent decay, and photoelectron images obtained through both resonant and non-resonant multiphoton ionization. The results are compared with our previously reported predissociation lifetime measurements for the band origin 000 [Gitzinger, J. Chem. Phys. 132, 234313 (2010)10.1063/1.3455207]. The result, previously reported in the literature, where vibrational excitation to the C-I stretching mode ( 3) of the CH 3I 3R 1(E) Rydberg state yields a predissociation lifetime about four times slower than that corresponding to the vibrationless state, whereas predissociation is twice faster if the vibrational excitation is to the umbrella mode ( 2), is confirmed in the present experiments. In addition to the specific vibrational state lifetimes, which were found to be 0.85 0.04 ps and 4.34 0.13 ps for the 201 and 301 vibronic levels, respectively, the time evolution of the fragment anisotropy and the vibrational activity of the CH 3 fragment are presented. Additional striking results found in the present work are the evidence of ground state I( 2P 32) fragment production when excitation is produced specifically to the 301 vibronic level, which is attributed to predissociation via the A-band 1Q 1 potential energy surface, and the indication of a fast adiabatic photodissociation process through the repulsive A-band 3A 1(4E) state, after direct absorption to this state, competing with absorption to the 301 vibronic level of the 3R 1(E) Rydberg state of the B-band.Peer Reviewe

Harmonic generation by atomic and nanoparticle precursors in a ZnS laser ablation plasma

Harmonic generation of a driving laser propagating across a laser ablation plasma serves for the diagnosis of multicomponent plumes. Here we study the contribution of atomic and nanoparticle precursors to the generation of coherent ultraviolet and vacuum ultraviolet light as low-order harmonics of the fundamental emission (1064 nm) of a Q-switched Nd:YAG laser in a nanosecond infrared ZnS laser ablation plasma. Odd harmonics from the 3rd up to the 9th order (118.2 nm) have been observed with distinct temporal and spatial characteristics which were determined by varying the delay between the ablation and driving nanosecond pulses and by spatially scanning the plasma with the focused driving beam propagating parallel to the target. At short distances from the target surface (≤1 mm), the harmonic intensity displays two temporal components peaked at around 250 ns and 10 μs. While the early component dies off quickly with increasing harmonic order and vanishes for the 9th order, the late component is notably intense for the 7th harmonic and is still clearly visible for the 9th. Spectral analysis of spontaneous plume emissions help to assign the origin of the two components. While the early plasma component is mainly constituted by neutral Zn atoms, the late component is mostly due to nanoparticles, which upon interaction with the driving laser are subject to breakup and ionization. With the aid of calculations of the phase matching integrals within the perturbative model of optical harmonic generation, these results illustrate how atom and nanoparticle populations, with differing temporal and spatial distributions within the ablation plasma, contribute to the nonlinear medium.Funding has been provided by Ministerio de Economía y Competitividad (MINECO) of Spain under Project CTQ2013-43086-P. I.L-Q., A.B-C. and M.O. thank respectively MINECO, for a FPI fellowship (BES-2011-044738), CSIC, for a JAE-TEC 2010 contract and CSIC for a contract. Fruitful discussions with Dr. Mikel Sanz and Prof. A. Gonzalez-Arroyo are acknowledged.Peer reviewe

Femtosecond pulsed laser deposition of nanostructured CdS films

In this work, we report an investigation of the properties of nanostructured deposits obtained from femtosecond pulsed laser deposition of CdS sintered targets. Specifically, we address the effects of laser irradiation wavelength, laser fluence, and substrate temperature (from 25 to 450 °C). The composition of the deposits was characterized using X-ray photoelectron spectroscopy (XPS), their crystallinity by X-ray diffraction (XRD), and the surface morphology was studied by environmental scanning electron microscopy (ESEM) and atomic force microscopy (AFM). It has been found that the smallest nanoparticles, with an average diameter of 25 nm and a narrow size distribution, together with particulates in the range of 80-120 nm, are obtained at the shortest laser wavelength of 266 nm on room-temperature substrates. Deposits do not contain microscopic droplets in any of the explored conditions. © 2010 American Chemical Society.Peer Reviewe

Low-order harmonic generation in a ZnS laser ablation plasma

Low-order (3rd to 9th) harmonic generation of a near-infrared driving laser (1064 nm) is reported in a laser ablation plasma of ZnS. Temporal analysis shows two distinct components with respect to the ablation event. The late temporal component exhibits high conversion efficiency for the highest harmonic orders observed. This is attributed to a dramatic modification of the plasma medium with the driving laser.Peer Reviewe

Probing orbital structure of polyatomic molecules by high-order harmonic generation (vol 98, art no 203007, 2007)

Publisher’s Note: Probing Orbital Structure of Polyatomic Molecules by High-Order Harmonic Generation [Phys. Rev. Lett. 98, 203007 (2007)

Femtosecond double-pulse laser ablation and deposition of Co-doped ZnS thin films

Nanostructured thin films of Co-doped zinc sulfide were synthesized through femtosecond pulsed laser deposition. The scheme involved ablation of physically mixed Co and ZnS with pairs of ultrashort pulses separated in time in the 0-300 ps range. In situ monitorization of the deposition process was carried out through a simultaneous reflectivity measurement. The crystallinity of generated nanoparticles and the inclusion of Co in the ZnS lattice is demonstrated by transmission electron microscopy and energy dispersive X-ray microanalysis (TEM-EDX) characterization. Surface morphology, Raman response, and photoluminescence of the films have also been assessed. The role of interpulse temporal separation is most visible in the thickness of the films obtained at the same total fluence, with much thicker films deposited with short delays than with individual uncoupled pulses. The proportion of Co in the synthesized doped ZnS nanoparticles is found to be substantially lower than the original proportion, and practically independent on interpulse delay