Suchergebnisse

8 págs.; 6 figs.; 1 tab. ; The photodissociation dynamics of the methyl radical from the 3s and 3pz Rydberg states have been studied using the velocity map and slice ion imaging in combination with pump–probe nanosecond laser pulses. The reported translational energy and angular distributions of the H(2S) photofragment detected by (2+1) REMPI highlight different dissociation mechanisms for the 3s and 3pz Rydberg states. A narrow peak in the translational energy distribution and an anisotropic angular distribution characterize the fast 3s photodissociation, while for the 3pz state Boltzmann-type translational energy and isotropic angular distributions are found. High level ab initio calculations have been performed in order to elucidate the photodissociation mechanisms from the two Rydberg states and to rationalize the experimental results. The calculated potential energy curves highlight a typical predissociation mechanism for the 3s state, characterized by the coupling between the 3s Rydberg state and a valence repulsive state. On the other hand, the photodissociation on the 3pz state is initiated by a predissociation process due to the coupling between the 3pz Rydberg state and a valence repulsive state and constrained, later on, by two conical intersections that allow the system to relax to lower electronic states. Such a mechanism opens up different reaction pathways leading to CH2 photofragments in different electronic states and inducing a transfer of energy between translational and internal modes. ; S. M. P. acknowledges financial support from Campus de Excelencia Internacional Moncloa and LASING S. A. D. V. C. acknowledges a contract from MINECO under the Fondo de Garantıía Juvenil. A. Z. thanks the support from the European Research Council under the European Union's 7th Framework Program (FP7/2007–2013)/ERC Grant agreement 610256 (NANOCOSMOS). M. G. G. is grateful to Spanish MINECO for a contract through Programa de Técnicos de Apoyo a Infraestructuras. This work has been financed by the Spanish MINECO (grants FIS2011- 29596-C02-01, CTQ2012-37404-C02-01, FIS2013-40626-P and CTQ2015-65033-P) and by COST Actions CM1401 and CM05. This research has been carried out within the Unidad Asociada Química Física Molecular between Departamento de Química Física of Universidad Complutense de Madrid (UCM) and Consejo Superior de Investigaciones Científicas (CSIC). The facilities provided by the Centro de Láseres Ultrarrápidos at UCM are acknowledged. The Centro de Supercomputación de Galicia (CESGA, Spain) and CTI (CSIC) are acknowledged for the use of their resources. ; Peer Reviewed

12 pags., 7 figs., 1 tab. ; The time-resolved photodynamics of the methyl iodide cation (CH3I+) are investigated by means of femtosecond XUV-IR pump-probe spectroscopy. A time-delay-compensated XUV monochromator is employed to isolate a specific harmonic, the 9th harmonic of the fundamental 800 nm (13.95 eV, 88.89 nm), which is used as a pump pulse to prepare the cation in several electronic states. A time-delayed IR probe pulse is used to probe the dissociative dynamics on the first excited state potential energy surface. Photoelectrons and photofragment ions - and I+ - are detected by velocity map imaging. The experimental results are complemented with high level ab initio calculations for the potential energy curves of the electronic states of CH3I+ as well as with full dimension on-the-fly trajectory calculations on the first electronically excited state, considering the presence of the IR pulse. The and I+ pump-probe transients reflect the role of the IR pulse in controlling the photodynamics of CH3I+ in the state, mainly through the coupling to the ground state and to the excited state manifold. Oscillatory features are observed and attributed to a vibrational wave packet prepared in the state. The IR probe pulse induces a coupling between electronic states leading to a slow depletion of fragments after the cation is transferred to the ground states and an enhancement of I+ fragments by absorption of IR photons yielding dissociative photoionization. ; MLMS acknowledges financial support through a predoctoral contract from Universidad Complutense de Madrid (Spain) and FULMATEN-CM project funded by Madrid Regional Government under programme Y2018/NMT-5028. GR thanks the Netherlands Organization for Scientific Research (NWO) for financial support (Rubicon 68-50-1410). This project has received funding (SMP) from the European Union's Horizon 2020 Research and Innovation Programme under the Marie Sklodowska-Curie Grant agreement No. 842539 (ATTO-CONTROL) and has been financed in part by the Spanish State Research Agency (AEI/10.13039/501100011033), Grants PGC2018-096444-B-I00, PID2019-106125GB-I00 and PID2019-106732GB-I00, and the Madrid Regional Government through the program Proyectos Sin´ergicos de I + D (Grant Y2018/NMT-5028 FULMATEN-CM). FM acknowledges support from the 'Severo Ochoa' Programme for Centres of Excellence in R & D (SEV-2016-0686) and the 'María de Maeztu' Programme for Units of Excellence in R & D (CEX2018-000805-M). All calculations were performed at the Mare Nostrum Supercomputer of the Red Española de Supercomputacion (BSC-RES) and the Centro de Computaci ´ on´ Científica de la Universidad Autonoma de Madrid (CCC-UAM). MV and OK acknowledge the support ´ from the Deutsche Forschungsgeminschaft (KO 4920/1-1). This work was performed in the Max Born Institut (Berlin) in the kHz Laboratory and received financial support from LaserLab Europe through the MBI002239 project.