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Spring Meeting of the European Materials Research Society (E-MRS) to be held as a VIRTUAL Conference from May 31st to June 3rd, 2021. .- https://www.european-mrs.com/meetings/2021-spring-meeting-0

The role of promoting and spectator modes vs energy randomization in nonadiabatic dynamics is interrogated in the photodissociation of methyl mercaptan, CH3SH, and dimethyl sulfide, CH3SCH3 or DMS, in the second absorption band. The primary CH3(ν) radicals produced in the dissociation of both systems at 210 nm have been resonantly detected in slice-imaging experiments, and the corresponding translational energy and angular distributions have been obtained. The stereodynamical information provided by Dixon’s bipolar moments in conjunction with the energy partitioning among the different degrees of freedom of the primary CH3(ν) products offers a panoramic picture of the photodissociation process of both systems. The remarkable similitude found between the two systems related to both vector correlations and internal energy content of the corresponding counterparts—SH for methyl mercaptan and SCH3 for DMS—indicates that despite the diabaticity of the process, no efficient energy randomization of the available energy takes place. More specifically, only the parent vibrational modes whose participation in the initial absorption step is imposed by the conical intersection—i.e., the promoting modes—are adiabatically preserved during the process, while the rest of the vibrational modes play the spectator role. The results for both molecules at 210 nm are complemented with experiments carried out for DMS at 201 nm to explore the internal mechanism of the conical intersection in different zones of the absorption region.

ECAMP13, Florence, Italy, April 8-12, 2019. -- https://www.ecamp13.org/, Interaction of intense laser light with solid targets causes a cascade of electronic, thermal and mechanical processes that eventually lead to ablation, i.e. ejection of material in the direction perpendicular to the target surface. Even for a fixed target, the characteristics of the laser pulses employed for ablation ¿mainly spectral region, fluence and pulse duration¿ can cause dramatically different transient states in the first stages of the processes, in terms of electron density, mechanical stress and temperature distribution, which in turn can produce ablation media of very different nature. On the other hand, in spite of the multiplicity of factors affecting the composition and dynamics of laser ablation plasmas, it has been found that for some areas of the parameter space, common characteristics appear. One notable example is the short pulse ablation of solids in the fluence range from 0.1 to 10 J cm-2, which is known to produce the ejection of matter largely in the form of nanoparticles [1], a phenomenon that has been observed for metals, semiconductors and insulators. Another is the characteristic spatial segregation of aggregates of different sizes [2], with lighter species concentrated in the leading part of the expanding medium and heavier species predominantly found in the trailing edge. In this work we experimentally explore common and distint features of laser ablation metal plasmas (Cu, Ag, Al) generated by femtosecond vs. nanosecond laser irradiation. The diagnosis of choice has been the measurement of the nonlinear optical response of the medium [3,4] through third harmonic generation, whose lack of species selectivity is compensated by its universality. With this methodology we have found species that are otherwise elusive, like middle-sized aggregates or cold nanoparticles, and through this universal detection, we have explored the limits of the degree of control attainable in the composition of the expanding media through the laser ablation conditions (see Fig. 1). We have found that atoms, clusters and nanoparticles are present in all conditions, but their relative importance can be dramatically altered for different ablation conditions. In particular, the combined role of fluence, focal geometry and pulse duration will be described. Fig. 1 Intensity of third optical harmonic generated in NIR laser ablation Cu plasmas at a distance of 1 mm from the surface as a function of delay time with respect to the ablation event, for three distinct irradiation schemes in terms of pulse duration and focusing conditions indicated on the graphs. Funding: This work has been funded by MINECO (Spain) though grant number CTQ2016-75880-P. References [1] T. Donnelly, J. G. Lunney, S. Amoruso, R. Bruzzese, X. Wang, X. Ni, Dynamics of the plumes produced by ultrafast laser ablation of metals, J. Appl. Phys. 108, 043309 (2010). [2] C. Wu, L. Zhigilei, Microscopic mechanisms of laser spallation and ablation of metal targets from large-scale molecular dynamics simulations, Appl. Phys. A: Mater. Sci. Process. 114, 11 (2014). [3] R. de Nalda, M. Lopez-Arias, M. Sanz, M. Oujja, M. Castillejo, Harmonic generation in ablation plasmas of wide bandgap semiconductors, Phys. Chem. Chem. Phys. 13, 10755 (2011). [4] M. Oujja, J.G. Izquierdo, L. Bañares, R. de Nalda, M. Castillejo, Observation of middle-sized metal clusters in femtosecond laser ablation plasmas through nonlinear optics, Phys. Chem. Chem. Phys. 20, 16956 (2018)., This work has been funded by MINECO (Spain) though grant number CTQ2016-75880-P.

IMAMPC2019, Madrid, 11 - 14 June, 2019, Funding from MINECO (Spain) through grants CTQ2015-65033-P and CTQ2016-75880-P is gratefully acknowledged.

10th International Meeting on Photodynamics and Related Aspects (IMPRA 2018), 3-7 September 2018. Universidad Nacional de Colombia. Hotel Las Américas, Cartagena de Indias, Colombia. .-http://ciencias.bogota.unal.edu.co/departamentos/quimica/impra2018/, Coulomb explosion in molecules occurs when more than one electron is ejected from the system, and its charged components undergo explosion due to the electrostatic repulsion. The complete measurement of the final velocity vectors of the resulting fragments can provide information on the geometry of molecules or clusters, the alignment or orientation of a molecular ensemble in the laboratory frame, and can even provide a tool for the identification of isomers or enantiomers. The potential offered by Coulomb explosion imaging to map nonadiabatic molecular dynamics will be discussed using the example of CH3I A-band dissociation.

Conferencia invitada. -- COST Action CM1401, Faro- (Portugal), 16-20 Jan 2017. -- https://astrochem2017.sciencesconf.org/, Several radical molecules of astrochemical interest have been studied theoretically in order to characterize the electronic states (and the couplings beteeen them) involved in the different photodissociation pathways leading to fragmentation of the radical. Specifically, the radicals studied are CH3, CH3CH2, and the methoxy family CH3X (X = O, S). Highly correlated ab initio techniques have been used in the studies. In the cases of CH3 [1]-[3] and CH3X (X = O, S) [4], the potential-energy surfaces and couplings for the corresponding ground and excited electronic states were characterized using a two-dimensional representation that includes the CH2-H and CH3-X dissociative coordinate and the CH2 and CH3 umbrella angle, respectively. For the CH3CH2 radical, there are three possible dissociative coordinates (namely CH3-CH2, CH3CH-H, and H-CH2CH2), and the different electronic states involved in those dissociation pathways have been characterized along with their corresponding couplings by using a one-dimensional representation in the above three dissociative coordinates [5]. The possible photodissociation mechanisms of the radical molecues studied are discussed in the light of the ab initio data obtained. Recent experimental results on the photodissociation of CH3 [1], [2] have been successfully interpreted with the aid of the present theoretical results., A. Bouallagui acknowledges the COST Action “Our Astrochemical History”, CM1401, for the grant of an STSM that made possible a short stay in the Instituto de Física Fundamental (CSIC) during which part of the work presented here was carried out.

MOLEC 2016, Toledo (Spain), 11 - 16 September 2016, The methoxy family CH3X (X = O, S) is a series of very interesting radicals from several perspectives [1]. They are important compounds in environmental and combustion chemistry, in astrophysics and atmospheric reactions. Numerous references to the practical importance of these radicals have been compiled [2]. Although the literature on CH3O and CH3S is quite extensive, the most germane works from the viewpoint of photodissociation dynamics are the spectroscopic [3] and theoretical investigations [1,4] of the electronic structure of methoxy. In the present work, new ab initio data have been calculated on the 2E, 2A1, 2A2, 4E, and 4A2 five electronic states of CH3O and CH3S that correlate with the asymptotes O(S)(3P) + CH3 and O(S)(1D) + CH3, including spin-orbit coupling for the first time. Potential energy surfaces for the above electronic states have been computed as a function of CO(CS) distance and OCH(SCH) angle under C3v symmetry, using multireference internally contracted single and double excitation configuration interaction method with the aug-cc-pCVQZ basis set. The possible photodissociation mechanisms of CH3O and CH3S are discussed in the light of these potentials.

MOLEC 2016, Toledo (Spain), 11 - 16 September 2016

MOLEC 2016, Toledo (Spain), 11 - 16 September 2016, Ethyl radical, C2H5, is an intermediate of central importance in hydrocarbon combustion [1]. As one of the simplest alkyl radicals, ethyl represents an important prototype for more dynamically complicated radicals. There have been numerous studies on the photodissociation process of this radical in order to elucidate its dissociation dynamics [2,3]. The photodissociation of the ethyl radical takes place by exciting the system to predissociative 3s or 3p Rydberg states, which can then decay into three product channels : CH3+CH2, CH2CH2+H and CHCH3+H. To gain some insight on the possible photodissociation mechanism, high level ab initio electronic structure calculations were carried out using multireference internally contracted single and double excitation configuration interaction method, with AVTZ basis sets. The adiabatic potential energy curves of the excited electronic states involved in the process have been calculated for the above three dissociation channels for the first time. The possible dissociation mechanisms are discussed.

AMOC 2015, Anharmonicity in médium-sized molecules and cluster, CSIC, Madrid (Spain), 26-30 April 2015; http://tct1.iem.csic.es/AMOC2015.htm

Wavefront aberrations play a major role when focusing an ultrashort laser pulse to a high-quality focal spot. Here, we report a novel method to measure and correct wavefront aberrations of a 30-fs pulsed laser beam. The method only requires a programmable liquid-crystal spatial light modulator and a camera. Wavefront retrieval is based on pupil segmentation with an annular lens array, which allows us to determine the local phase that mini- mizes focusing errors due to wavefront aberrations. Our method provides accurate results even when implemented with low dynamic range cameras and polychromatic beams. Finally, the retrieved phase is added to a diffractive lens codified onto the spatial light modulator to experi- mentally demonstrate near-diffraction-limited femtosecond beam focusing without refractive components.

Trabajo presentado en la 12th Conference on Laser Ablation, celebrada en Nápoles (Italia) del 06 al 11 de octubre de 2013., Transition metal doped II-VI materials are widely investigated for applications as diluted magnetic semiconductors (DMS) [1]. Fundamental insight into the interaction dynamics of fs laser pulses with suitable Co/Zn/S targets can provide information on the temporal regime in which the laser energy couples with different ablation pathways and can help to design strategies for the controlled growth of the above materials by pulsed laser ablation and deposition (PLD). In this work, we have investigated the ultrafast laser ablation dynamics of Co/Zn/S targets with a pump-and-probe fs laser scheme, combined with time-of-flight mass spectrometry to analyze the dependence of the ejected plasma composition on the time delay between the pulses. Finally, a two-pulse fs-PLD setup is used to investigate the imprint of relative delays and energies on the composition and properties of the deposited Co/Zn/S material.

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13 pags. 3 figs., The low temperature ( < 100K) relaxation of N2 in self-collisions and in collisions with He and Ne has been experimentally studied with resonance-enhanced-multiphoton-ionization and time-of-flight techniques. The following average values of the rotational relaxation cross sections, σr, have been derived from the measurements: σr N2-N2 (T = 5-60 K) ≈ 35 Å2; σr N2-He (T = 5-80 K) ≈ 15 Å2 and σr N2-Ne (T = 5-60 K) ≈ 40 Å2. The cross section trend σr N2-N2 ≈ σr N2-Ne > σr N2-He reported in the literature for T = 300K is confirmed below 100K, but the absolute values are larger in the low temperature range. © 2002 Elsevier Science Ltd. All rights reserved., Financial support: SEUID of Spain (Project PB98-0762-C03-02)

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