Person: Marggi Poullaín, Sonia
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First Name
Sonia
Last Name
Marggi Poullaín
Affiliation
Universidad Complutense de Madrid
Faculty / Institute
Ciencias Químicas
Department
Química Física
Area
Química Física
Identifiers
4 results
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Item Photodissociation dynamics of bromoiodomethane from the first and second absorption bands. A combined velocity map and slice imaging study(Physical Chemistry Chemical Physics, 2018) Marggi Poullaín, Sonia; Chicharro, David ; Navarro, Eduardo; Rubio-Lago, Luis; González-Vázquez, Jesús; Bañares Morcillo, LuisThe photodissociation dynamics of bromoiodomethane (CH2BrI) have been investigated at the maximum of the first A and second A′ absorption bands, at 266 and 210 nm excitation wavelengths, respectively, using velocity map and slice imaging techniques in combination with a probe detection of both iodine and bromine fragments, I(2P3/2), I*(2P1/2), Br(2P3/2) and Br*(2P1/2) via (2 + 1) resonance enhanced multiphoton ionization. Experimental results, i.e. translational energy and angular distributions, are reported and discussed in conjunction with high level ab initio calculations of potential energy curves and absorption spectra. The results indicate that in the A-band, direct dissociation through the 5A′ excited state leads to the I(2P3/2) channel while I*(2P1/2) atoms are produced via the 5A′ → 4A′/4A′′ nonadiabatic crossing. The presence of Br and Br* fragments upon excitation to the A-band is attributed to indirect dissociation via a curve crossing between the 5A′ with upper excited states such as the 9A′. The A′-band is characterized by a strong photoselectivity leading exclusively to the Br(2P3/2) and Br*(2P1/2) channels, which are likely produced by dissociation through the 9A′ excited state. Avoided crossings between several excited states from both the A and A′ bands entangle however the possible reaction pathways.Item A velocity-map imaging study of the photodissociation of the methyl iodide cation(Physical Chemistry Chemical Physics, 2017) Marggi Poullaín, Sonia; Chicharro Vacas, David; Rubio-Lago, Luis; González-Vázquez, Jesús; Bañares Morcillo, LuisThe photodissociation dynamics of the methyl iodide cation has been studied using the velocity map imaging technique. A first laser pulse is used to ionize methyl iodide via a (2 + 1) REMPI scheme through the 5pp - 6p Rydberg state two-photon transition. The produced CH3I+(X) ions are subsequently excited at several wavelengths between 242 and 260 nm. The reported translational energy distributions for the methyl and iodine ions present a Boltzmann-type unstructured distribution at low excitation energies as well as a recoiled narrow structure at higher excitation energies highlighting two different dissociation processes. High level ab initio calculations have been performed in order to obtain a deeper understanding of the photodissociation dynamics of the CH3I+ ion. Direct dissociation on a repulsive state from the manifold of states representing the B˜ excited state leads to CH3+(X) + I*(2P1/2), while the CH3 + I+(3P2) channel is populated through an avoided crossing outside the Franck–Condon region. In contrast, an indirect process involving the transfer of energy from highly excited electronic states to the ground state of the ion is responsible for the observed Boltzmann-type distributions.Item Site-specific hydrogen-atom elimination in photoexcited ethyl radical(Chemical Science, 2019) Chicharro Vacas, David; Marggi Poullaín, Sonia; Zanchet, Alexandre; Bouallagui, Aymen; García-Vela, Alberto; Senent, María ; Rubio-Lago, Luis; Bañares Morcillo, LuisThe photochemistry of the ethyl radical following excitation to the 3p Rydberg state is investigated in a joint experimental and theoretical study. Velocity map images for hydrogen atoms detected from photoexcited isotopologues CH3CH2, CH3CD2 and CD3CH2 at 201 nm, are discussed along with high-level ab initio electronic structure calculations of potential energy curves and non-adiabatic coupling matrix elements (NACME). A novel mechanism governed by a conical intersection allowing prompt site-specific hydrogen-atom elimination is presented and discussed. For this mechanism to occur, an initial rovibrational excitation is allocated to the radical permitting to access this reaction pathway and thus to control the ethyl photochemistry. While hydrogen-atom elimination from cold ethyl radicals occurs through internal conversion into lower electronic states followed by slow statistical dissociation, prompt site-specific Ca elimination into CH3CH + H, occurring through a fast non-adiabatic crossing to a valence bound state followed by dissociation through a conical intersection, is accessed by means of an initial ro-vibrational energy content into the radical. The role of a particularly effective vibrational promoting mode in this prompt photochemical reaction pathway is discussed.Item Site-specific hydrogen-atom elimination in photoexcited alkyl radicals(Physical Chemistry Chemical Physics, 2021) Chicharro Vacas, David; Zanchet, Alexandre; Bouallagui, Aymen; Rubio-Lago, Luis; García-Vela, Alberto; Bañares Morcillo, Luis; Marggi Poullaín, SoniaA prompt site-specific hydrogen-atom elimination from the α-carbon atom (Cα) has been recently reported to occur in the photodissociation of ethyl radicals following excitation at 201 nm [Chicharro et al., Chem. Sci., 2019, 10, 6494]. Such pathway was accessed by means of an initial ro-vibrational energy characterizing the radicals produced by in situ photolysis of a precursor. Here, we present experimental evidence of a similar dynamics in a series of alkyl radicals (C2H5, n-C3H7, n-C4H9, and i-C3H7) containing the same reaction coordinate, but different extended structures. The main requirements for the site-specific mechanism in the studied radicals, namely a rather high content of internal energy prior to dissociation and the participation of vibrational promoting modes, is discussed in terms of the chemical structure of the radicals. The methyl deformation mode in all alkyl radicals along with the CH bending motion in i-C3H7 appear to promote this fast H-atom elimination channel. The photodissociation dynamics of the simplest unsaturated alkyl radical, the vinyl radical (C2H3), is also discussed, showing no signal of site-specific fast H-atom elimination. The results are complemented with high-level ab initio electronic structure calculations of potential energy curves of the vinyl radical, which are compared with those previously reported for the ethyl radical.