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Real time photodissociation of dihalomethanes has been measured by femtosecond velocity map imaging to disentangle the effect of the halogen-atom on the carbon–iodine cleavage dynamics., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Multiphoton ionization (MPI) of alkyl iodides (RI, R = CnH2n+1, n = 1–4) has been investigated with femtosecond laser pulses centered at 800 and 400 nm along with photoelectron imaging detection. In addition, the ultraviolet (UV)–vacuum ultraviolet (VUV) absorption spectra of gas-phase RIs have been measured in the photon energy range of 5–11 eV using the VUV Fourier transform spectrometer at the VUV DESIRS beamline of the synchrotron SOLEIL facility. The use of high-laser-field strengths in matter–radiation interaction generates highly non-linear phenomena, such as the Stark shift effect, which distorts the potential energy surfaces of molecules by varying both the energy of electronic and rovibrational states and their ionization energies. The Stark shift can then generate resonances between intermediate states and an integer number of laser photons of a given wavelength, which are commonly known as Freeman resonances. Here, we study how the molecular structure of linear and branched alkyl iodides affects the UV–VUV absorption spectrum, the MPI process, and the generation of Freeman resonances. The obtained results reveal a dominant resonance in the experiments at 800 nm, which counter-intuitively appears at the same photoelectron kinetic energy in the whole alkyl iodide series. The ionization pathways of this resonance strongly involve the 6p( 2 E3/2) Rydberg state with different degrees of vibrational excitation, revealing an energy compensation effect as the R-chain complexity increases, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Clocking of electronically and vibrationally state-resolved channels of the fast photodissociation of CH3I in the A-band is re-examined in a combined experimental and theoretical study. Experimentally, a femtosecond pump-probe scheme is employed in the modality of resonant probing by resonance enhanced multiphoton ionization (REMPI) of the methyl fragment in different vibrational states and detection through fragment velocity map ion (VMI) imaging as a function of the time delay. We revisit excitation to the center of the A-band at 268 nm and report new results for excitation to the blue of the band center at 243 nm. Theoretically, two approaches have been employed to shed light into the observations: first, a reduced dimensionality 4D nonadiabatic wavepacket calculation using the potential energy surfaces by Xie et al. [J. Phys. Chem. A 104, 1009 (2000)]; and second, a full dimension 9D trajectory surface-hopping calculation on the same potential energy surfaces, including the quantization of vibrational states of the methyl product. In addition, high level ab initio electronic structure calculations have been carried out to describe the CH3 3pz Rydberg state involved in the (2 + 1) REMPI probing process, as a function of the carbon-iodine (C–I) distance. A general qualitative agreement is obtained between experiment and theory, but the effect of methyl vibrational excitation in the umbrella mode on the clocking times is not well reproduced. The theoretical results reveal that no significant effect on the state-resolved appearance times is exerted by the nonadiabatic crossing through the conical intersection present in the first absorption band. The vibrationally state resolved clocking times observed experimentally can be rationalized when the (2 + 1) REMPI probing process is considered. None of the other probing methods applied thus far, i.e., multiphoton ionization photoelectron spectroscopy, soft X-ray inner-shell photoelectron spectroscopy, VUV single, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Femtosecond velocity map imaging to disentangle the electronic predissociation of ethyl iodide in the B-band., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Multiphoton ionization (MPI) of alkyl iodides (RI, R = CnH2n+1, n = 1–4) has been investigated with femtosecond laser pulses centered at 800 and 400 nm along with photoelectron imaging detection. In addition, the ultraviolet (UV)–vacuum ultraviolet (VUV) absorption spectra of gas-phase RIs have been measured in the photon energy range of 5–11 eV using the VUV Fourier transform spectrometer at the VUV DESIRS beamline of the synchrotron SOLEIL facility. The use of high-laser-field strengths in matter–radiation interaction generates highly non-linear phenomena, such as the Stark shift effect, which distorts the potential energy surfaces of molecules by varying both the energy of electronic and rovibrational states and their ionization energies. The Stark shift can then generate resonances between intermediate states and an integer number of laser photons of a given wavelength, which are commonly known as Freeman resonances. Here, we study how the molecular structure of linear and branched alkyl iodides affects the UV–VUV absorption spectrum, the MPI process, and the generation of Freeman resonances. The obtained results reveal a dominant resonance in the experiments at 800 nm, which counter-intuitively appears at the same photoelectron kinetic energy in the whole alkyl iodide series. The ionization pathways of this resonance strongly involve the 6p( 2 E3/2) Rydberg state with different degrees of vibrational excitation, revealing an energy compensation effect as the R-chain complexity increases, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

El ioduro de metilo (CH3I) se ha convertido en el sistema de referencia para estudios de fotodisociación molecular en la región ultravioleta (UV). Esta molécula presenta tanto dinámicas defotodisociación directa como de predisociación, que conducen a la escisión del enlace C–I, relativamentesimples pero interesante, así como abordable por cálculos teóricos gracias a su estructura de moléculapseudo-diatómica. En concreto, ha sido de interés de diversos experimentadores investigar cómo ladinámica de este sistema simple puede ser modificada a lo largo de la coordenada de reacción, mediantela realización de cambios en su estructura; bien, aumentando el tamaño de la cadena hidrocarbonada,creando ramificaciones, introduciendo insaturaciones o algún átomo sustituyente e incluso ionizando lamolécula para acceder al catión en diferentes estados electrónicos..., Methyl iodide (CH3I) has become a reference system for molecular photodissociation studies inthe ultraviolet (UV) region. This molecule presents direct photodissociation as well as predissociationmechanisms, leading to the cleavage of the C−I bond, relatively simple but attractive due to the presenceof conical intersections and non-adiabatic crossing as well as approachable by theoretical calculationsthanks to its pseudo-diatomic structure. In particular, it has been of interest to several experimentershow the photoinduced dynamics of this simple system can be modified along the reaction coordinatethrough changes in the molecular structure; either by increasing the size of the hydrocarbon chain, bycreating branches, introducing unsaturations, or some substituting halogen atoms or ionizing themolecule to get the cation in different electronic states...

Clocking of electronically and vibrationally state-resolved channels of the fast photodissociation of CH3I in the A-band is re-examined in a combined experimental and theoretical study. Experimentally, a femtosecond pump-probe scheme is employed in the modality of resonant probing by resonance enhanced multiphoton ionization (REMPI) of the methyl fragment in different vibrational states and detection through fragment velocity map ion (VMI) imaging as a function of the time delay. We revisit excitation to the center of the A-band at 268 nm and report new results for excitation to the blue of the band center at 243 nm. Theoretically, two approaches have been employed to shed light into the observations: first, a reduced dimensionality 4D nonadiabatic wavepacket calculation using the potential energy surfaces by Xie et al. [J. Phys. Chem. A 104, 1009 (2000)]; and second, a full dimension 9D trajectory surface-hopping calculation on the same potential energy surfaces, including the quantization of vibrational states of the methyl product. In addition, high level ab initio electronic structure calculations have been carried out to describe the CH3 3pz Rydberg state involved in the (2 + 1) REMPI probing process, as a function of the carbon-iodine (C–I) distance. A general qualitative agreement is obtained between experiment and theory, but the effect of methyl vibrational excitation in the umbrella mode on the clocking times is not well reproduced. The theoretical results reveal that no significant effect on the state-resolved appearance times is exerted by the nonadiabatic crossing through the conical intersection present in the first absorption band. The vibrationally state resolved clocking times observed experimentally can be rationalized when the (2 + 1) REMPI probing process is considered. None of the other probing methods applied thus far, i.e., multiphoton ionization photoelectron spectroscopy, soft X-ray inner-shell photoelectron spectroscopy, VUV single-photon i, Ministerio de Ciencia, Invocación y Universidades (España), Ministerio de Economía y Competitividad (España), Universidad Complutense de Madrid, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Ultrashort XUV wavelength-selected pulses obtained with high harmonic generation are used to study the dynamics of molecular cations with state-to-state resolution. We demonstrate this by XUV pump - IR probe experiments on CH3I+ cations and identify both resonant and non-resonant dynamics., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Ultrashort XUV wavelength-selected pulses obtained with high harmonic generation are used to study the dynamics of molecular cations with state-to-state resolution. We demonstrate this by XUV pump - IR probe experiments on CH3I+ cations and identify both resonant and non-resonant dynamics., Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Femtosecond velocity map imaging to disentangle the electronic predissociation of ethyl iodide in the B-band., European Commission, Comunidad de Madrid, Ministerio de Economía y Competitividad (España), Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

Real time photodissociation of dihalomethanes has been measured by femtosecond velocity map imaging to disentangle the effect of the halogen-atom on the carbon–iodine cleavage dynamics., Universidad Complutense de Madrid, Ministerio de Economía y Competitividad (España), European Commission, Comunidad de Madrid, Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub

The real time photodissociation of chloroiodomethane (CH2ICl) in the first absorption band at 268 nm is reported in comparison with the well-known methyl iodide (CH3I) in order to investigate the halogen-atom substituent effect on the time-resolved photodynamics of halomethanes. Femtosecond velocity map imaging measurements in conjunction with resonance enhanced multiphoton ionization (REMPI) to detect the iodine fragments have been performed to obtain translational energy, angular distributions and the photodissociation reaction times. High level ab initio and on-the-fly trajectory calculations have been carried out to rationalize the experimental results in terms of the excited states involved and the dissociation mechanisms., Universidad Complutense de Madrid, Ministerio de Economía y Competitividad (España), Depto. de Química Física, Fac. de Ciencias Químicas, TRUE, pub