Imaging the photodissociation dynamics of the methyl radical from the 3s and 3pz Rydberg states

Abstract

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