Alberto García-vela - Academia.edu (original) (raw)
Papers by Alberto García-vela
The Journal of Physical Chemistry A
VUV photoionization of the CH n I radicals (with n = 0, 1, and 2) is investigated by means of syn... more VUV photoionization of the CH n I radicals (with n = 0, 1, and 2) is investigated by means of synchrotron radiation coupled with a double imaging photoion-photoelectron coincidence spectrometer. Photoionization efficiencies and threshold photoelectron spectra (TPES) for photon energies ranging between 9.2 and 12.0 eV are reported. An adiabatic ionization energy (AIE) of 8.334 ± 0.005 eV is obtained for CH 2 I, which is in good agreement with previous results [8.333 ± 0.015 eV, Sztáray et al. J. Chem. Phys. 2017, 147, 013944], while for CI an AIE of 8.374 ± 0.005 eV is measured for the first time and a value of ∼8.8 eV is estimated for CHI. Ab initio calculations have been carried out for the ground state of the CH 2 I radical and for the ground state and excited states of the radical cation CH 2 I + , including potential energy curves along the C−I coordinate. Franck−Condon factors are calculated for transitions from the CH 2 I(X̃2B 1) ground state of the neutral radical to the ground state and excited states of the radical cation. The TPES measured for the CH 2 I radical shows several structures that correspond to the photoionization into excited states of the radical cation and are fully assigned on the basis of the calculations. The TPES obtained for the CHI is characterized by a broad structure peaking at 9.335 eV, which could be due to the photoionization from both the singlet and the triplet states and into one or more electronic states of the cation. A vibrational progression is clearly observed in the TPES for the CI radical and a frequency for the C−I stretching mode of 760 ± 60 cm −1 characterizing the CI + electronic ground state has been extracted.
Physical Chemistry Chemical Physics
The photodissociation dynamics of the ethyl radical following excitation into the 3s and 3p Rydbe... more The photodissociation dynamics of the ethyl radical following excitation into the 3s and 3p Rydberg states are revisited in a joint experimental and theoretical study. Two different methods to produce...
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, Jan 28, 2017
Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally st... more Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally studied using pump-probe schemes where a first laser pulse induces the process under study and a second one detects the produced fragments. Providing an efficient detection of ro-vibrationally state-selected photofragments, the resonance enhanced multiphoton ionization (REMPI) technique is, without question, the most popular approach used for the probe step, while non-resonant multiphoton ionization (NRMPI) detection of the products is scarce. The main goal of this work is to test the sensitivity of the NRMPI technique to fragment vibrational distributions arising from molecular photodissociation processes. We revisit the well-known process of methyl iodide photodissociation in the A-band at around 280 nm, using the velocity-map imaging technique in conjunction with NRMPI of the methyl fragment. The detection wavelength, carefully selected to avoid any REMPI transition, was scanned between...
Phys. Chem. Chem. Phys., 2016
The postpulse transient phase modulation effects observed on fragment populations are explained i... more The postpulse transient phase modulation effects observed on fragment populations are explained in terms of the mechanism of interference between overlapping resonances.
RSC Adv., 2014
Realistic wave packet simulations demonstrate that the signature of control of the survival proba... more Realistic wave packet simulations demonstrate that the signature of control of the survival probability and lifetime of a specific resonance state can be observed and probed in typical time-resolved pump–probe experiments.
The Journal of Physical Chemistry A, 2009
The He-I(2)(B, v) resonances embedded in the continuum of the v = 60 and 59 vibrational manifolds... more The He-I(2)(B, v) resonances embedded in the continuum of the v = 60 and 59 vibrational manifolds are investigated. Such states manifest a nature of overlapping and long-lived orbiting resonances, which are supported by centrifugal barriers originated in internal rotational excitation of I(2) and He within the complex. The same number of orbiting resonances, six, is found for v = 60 and for v = 59, with similar energy positions and wave functions, indicating that the spectrum of orbiting resonances changes slowly with the vibrational state v. Three of the orbiting resonances appear at nearly the same energies as the peaks observed experimentally in the vibrational relaxation cross section of I(2)(B, v = 21) through low temperature collisions with He. Such finding suggests that the cross section peaks have their origin in orbiting resonances of the He-I(2)(B, v = 21) complex formed upon the collision.
The Journal of Physical Chemistry A, 2002
The fragmentation dynamics of Ar-HCl following ultraviolet photoexcitation is studied both classi... more The fragmentation dynamics of Ar-HCl following ultraviolet photoexcitation is studied both classically and by an exact wave packet calculation. The focus of the analysis is on the partial fragmentation pathway Ar-HCl + hν f H + Ar-Cl. The results suggest that there is a competition between two different and simultaneous dissociation mechanisms of hydrogen, namely, direct dissociation and indirect dissociation involving a collision between H and Ar. These two dissociation mechanisms populate different states of partial fragmentation and total fragmentation (into H + Ar + Cl), which interfere upon the H/Ar collision. A global interpretation of the photolysis process based on the interference between the two types of dissociation and consistent with all the quantum results found is proposed. Such an interpretation appears to be general for the UV photolysis of a wide variety of hydrogen-bonded clusters. A means to control the interference mechanism in order to enhance the yield of a specific fragmentation pathway is suggested.
The Journal of Physical Chemistry A, 2002
The Journal of Physical Chemistry A, 2014
The effect of intermolecular excitation on the vibrational predissociation lifetime is investigat... more The effect of intermolecular excitation on the vibrational predissociation lifetime is investigated systematically for different vdW complexes Rg-X2(B, v') (Rg = rare gas atom, X = halogen atom) by means of wave packet simulations. The lifetime as a function of intermolecular excitation displays a pattern of maxima and minima, with a similar shape for the different Rg-X2(B, v') complexes. The pattern is consistent with previous experimental findings involving lifetimes of intermolecular excitations in similar systems. The structure of the lifetime pattern is found to be determined by the shape of the resonance wave functions in the two van der Waals degrees of freedom, and more specifically by the magnitude of the overlap between the wave function and the coupling responsible for predissociation. Lifetime maxima and minima are associated with minima and maxima of this overlap, respectively. Implications for control of the complex lifetime are discussed.
Physical Chemistry Chemical Physics, 2012
The temperature dependence of the state-to-state vibrational relaxation rate constant ͑k 21−⌬ ͒ f... more The temperature dependence of the state-to-state vibrational relaxation rate constant ͑k 21−⌬ ͒ for collisions between I 2 ͑B , Ј =21͒ and He at very low kinetic energies was studied. The fluorescence from I 2 ͑B , Ј =21−⌬Ј͒ with ⌬Ј =1-5 indicates that in the temperature range of 0.6-8.2 K these states are populated by only one collision with He. The behavior of k 21−⌬ with temperature can be divided into two groups. The group with quantum changes ⌬Ј =1-3 shows scattering resonances in the low temperature region, with a general monotonical decrease of the rate constant with temperature, suggesting the importance of van der Waals interactions. This behavior is supported by the calculation of the probability of tunneling through the centrifugal barriers. For collisions in which 4-5 quanta are lost in a single event, there are no evidences of scattering resonances and the values of the relaxation rate constants could be determined only at the highest temperatures of this study. This suggests that relaxation occurs via impulsive collisions. The branching ratios for each channel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with ⌬Ј.
The Journal of Physical Chemistry Letters, 2012
ABSTRACT The lifetime of a resonance state overlapping with a second resonance is shown to be str... more ABSTRACT The lifetime of a resonance state overlapping with a second resonance is shown to be strongly enhanced (by a factor of 3) by combining two pump pulses to simultaneously excite the two resonances. Such an enhancement is produced by interference effects occurring between the two coherently excited overlapping resonances. A high degree of control on the intensity of interference, and thus on the resonance lifetime enhancement, is found to be achieved by varying the delay time between the pulses and their relative intensities.
The Journal of Chemical Physics, 1996
The Journal of Chemical Physics, 1999
The Journal of Chemical Physics, 1995
ABSTRACT
The Journal of Chemical Physics, 1996
The Journal of Chemical Physics, 2000
 van der Waals complex including three-body effects](https://attachments.academia-assets.com/73129908/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2005
An empirical intermolecular potential surface is proposed for the He-I 2 ͑B 3 ⌸ u ͒ complex, mode... more An empirical intermolecular potential surface is proposed for the He-I 2 ͑B 3 ⌸ u ͒ complex, modeled as a sum of pairwise He-I Morse interactions plus a three-body interaction term. The potential reproduces with very good agreement the spectral blueshifts and vibrational predissociation lifetimes measured for He-I 2 ͑B , Ј͒ in the range Ј= 10-67 of I 2 vibrational excitations. In particular, the accuracy achieved in the description of the experimental data for high Ј levels is attributed to the three-body interaction term included in the potential. The behavior of the potential surface with the I-I separation is analyzed and correlated with the experimental findings.
![Research paper thumbnail of Calculation of Cl[sub 2] vibrational distributions after vibrational predissociation of He[sub 2]–Cl[sub 2]](https://attachments.academia-assets.com/73129906/thumbnails/1.jpg)
](The Journal of Chemical Physics, 2005
The Journal of Physical Chemistry A
VUV photoionization of the CH n I radicals (with n = 0, 1, and 2) is investigated by means of syn... more VUV photoionization of the CH n I radicals (with n = 0, 1, and 2) is investigated by means of synchrotron radiation coupled with a double imaging photoion-photoelectron coincidence spectrometer. Photoionization efficiencies and threshold photoelectron spectra (TPES) for photon energies ranging between 9.2 and 12.0 eV are reported. An adiabatic ionization energy (AIE) of 8.334 ± 0.005 eV is obtained for CH 2 I, which is in good agreement with previous results [8.333 ± 0.015 eV, Sztáray et al. J. Chem. Phys. 2017, 147, 013944], while for CI an AIE of 8.374 ± 0.005 eV is measured for the first time and a value of ∼8.8 eV is estimated for CHI. Ab initio calculations have been carried out for the ground state of the CH 2 I radical and for the ground state and excited states of the radical cation CH 2 I + , including potential energy curves along the C−I coordinate. Franck−Condon factors are calculated for transitions from the CH 2 I(X̃2B 1) ground state of the neutral radical to the ground state and excited states of the radical cation. The TPES measured for the CH 2 I radical shows several structures that correspond to the photoionization into excited states of the radical cation and are fully assigned on the basis of the calculations. The TPES obtained for the CHI is characterized by a broad structure peaking at 9.335 eV, which could be due to the photoionization from both the singlet and the triplet states and into one or more electronic states of the cation. A vibrational progression is clearly observed in the TPES for the CI radical and a frequency for the C−I stretching mode of 760 ± 60 cm −1 characterizing the CI + electronic ground state has been extracted.
Physical Chemistry Chemical Physics
The photodissociation dynamics of the ethyl radical following excitation into the 3s and 3p Rydbe... more The photodissociation dynamics of the ethyl radical following excitation into the 3s and 3p Rydberg states are revisited in a joint experimental and theoretical study. Two different methods to produce...
Philosophical transactions. Series A, Mathematical, physical, and engineering sciences, Jan 28, 2017
Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally st... more Chemical reaction dynamics and, particularly, photodissociation in the gas phase are generally studied using pump-probe schemes where a first laser pulse induces the process under study and a second one detects the produced fragments. Providing an efficient detection of ro-vibrationally state-selected photofragments, the resonance enhanced multiphoton ionization (REMPI) technique is, without question, the most popular approach used for the probe step, while non-resonant multiphoton ionization (NRMPI) detection of the products is scarce. The main goal of this work is to test the sensitivity of the NRMPI technique to fragment vibrational distributions arising from molecular photodissociation processes. We revisit the well-known process of methyl iodide photodissociation in the A-band at around 280 nm, using the velocity-map imaging technique in conjunction with NRMPI of the methyl fragment. The detection wavelength, carefully selected to avoid any REMPI transition, was scanned between...
Phys. Chem. Chem. Phys., 2016
The postpulse transient phase modulation effects observed on fragment populations are explained i... more The postpulse transient phase modulation effects observed on fragment populations are explained in terms of the mechanism of interference between overlapping resonances.
RSC Adv., 2014
Realistic wave packet simulations demonstrate that the signature of control of the survival proba... more Realistic wave packet simulations demonstrate that the signature of control of the survival probability and lifetime of a specific resonance state can be observed and probed in typical time-resolved pump–probe experiments.
The Journal of Physical Chemistry A, 2009
The He-I(2)(B, v) resonances embedded in the continuum of the v = 60 and 59 vibrational manifolds... more The He-I(2)(B, v) resonances embedded in the continuum of the v = 60 and 59 vibrational manifolds are investigated. Such states manifest a nature of overlapping and long-lived orbiting resonances, which are supported by centrifugal barriers originated in internal rotational excitation of I(2) and He within the complex. The same number of orbiting resonances, six, is found for v = 60 and for v = 59, with similar energy positions and wave functions, indicating that the spectrum of orbiting resonances changes slowly with the vibrational state v. Three of the orbiting resonances appear at nearly the same energies as the peaks observed experimentally in the vibrational relaxation cross section of I(2)(B, v = 21) through low temperature collisions with He. Such finding suggests that the cross section peaks have their origin in orbiting resonances of the He-I(2)(B, v = 21) complex formed upon the collision.
The Journal of Physical Chemistry A, 2002
The fragmentation dynamics of Ar-HCl following ultraviolet photoexcitation is studied both classi... more The fragmentation dynamics of Ar-HCl following ultraviolet photoexcitation is studied both classically and by an exact wave packet calculation. The focus of the analysis is on the partial fragmentation pathway Ar-HCl + hν f H + Ar-Cl. The results suggest that there is a competition between two different and simultaneous dissociation mechanisms of hydrogen, namely, direct dissociation and indirect dissociation involving a collision between H and Ar. These two dissociation mechanisms populate different states of partial fragmentation and total fragmentation (into H + Ar + Cl), which interfere upon the H/Ar collision. A global interpretation of the photolysis process based on the interference between the two types of dissociation and consistent with all the quantum results found is proposed. Such an interpretation appears to be general for the UV photolysis of a wide variety of hydrogen-bonded clusters. A means to control the interference mechanism in order to enhance the yield of a specific fragmentation pathway is suggested.
The Journal of Physical Chemistry A, 2002
The Journal of Physical Chemistry A, 2014
The effect of intermolecular excitation on the vibrational predissociation lifetime is investigat... more The effect of intermolecular excitation on the vibrational predissociation lifetime is investigated systematically for different vdW complexes Rg-X2(B, v') (Rg = rare gas atom, X = halogen atom) by means of wave packet simulations. The lifetime as a function of intermolecular excitation displays a pattern of maxima and minima, with a similar shape for the different Rg-X2(B, v') complexes. The pattern is consistent with previous experimental findings involving lifetimes of intermolecular excitations in similar systems. The structure of the lifetime pattern is found to be determined by the shape of the resonance wave functions in the two van der Waals degrees of freedom, and more specifically by the magnitude of the overlap between the wave function and the coupling responsible for predissociation. Lifetime maxima and minima are associated with minima and maxima of this overlap, respectively. Implications for control of the complex lifetime are discussed.
Physical Chemistry Chemical Physics, 2012
The temperature dependence of the state-to-state vibrational relaxation rate constant ͑k 21−⌬ ͒ f... more The temperature dependence of the state-to-state vibrational relaxation rate constant ͑k 21−⌬ ͒ for collisions between I 2 ͑B , Ј =21͒ and He at very low kinetic energies was studied. The fluorescence from I 2 ͑B , Ј =21−⌬Ј͒ with ⌬Ј =1-5 indicates that in the temperature range of 0.6-8.2 K these states are populated by only one collision with He. The behavior of k 21−⌬ with temperature can be divided into two groups. The group with quantum changes ⌬Ј =1-3 shows scattering resonances in the low temperature region, with a general monotonical decrease of the rate constant with temperature, suggesting the importance of van der Waals interactions. This behavior is supported by the calculation of the probability of tunneling through the centrifugal barriers. For collisions in which 4-5 quanta are lost in a single event, there are no evidences of scattering resonances and the values of the relaxation rate constants could be determined only at the highest temperatures of this study. This suggests that relaxation occurs via impulsive collisions. The branching ratios for each channel are also temperature dependent and this behavior also suggests that the energy transfer mechanism changes with ⌬Ј.
The Journal of Physical Chemistry Letters, 2012
ABSTRACT The lifetime of a resonance state overlapping with a second resonance is shown to be str... more ABSTRACT The lifetime of a resonance state overlapping with a second resonance is shown to be strongly enhanced (by a factor of 3) by combining two pump pulses to simultaneously excite the two resonances. Such an enhancement is produced by interference effects occurring between the two coherently excited overlapping resonances. A high degree of control on the intensity of interference, and thus on the resonance lifetime enhancement, is found to be achieved by varying the delay time between the pulses and their relative intensities.
The Journal of Chemical Physics, 1996
The Journal of Chemical Physics, 1999
The Journal of Chemical Physics, 1995
ABSTRACT
The Journal of Chemical Physics, 1996
The Journal of Chemical Physics, 2000
The Journal of Chemical Physics, 2005
An empirical intermolecular potential surface is proposed for the He-I 2 ͑B 3 ⌸ u ͒ complex, mode... more An empirical intermolecular potential surface is proposed for the He-I 2 ͑B 3 ⌸ u ͒ complex, modeled as a sum of pairwise He-I Morse interactions plus a three-body interaction term. The potential reproduces with very good agreement the spectral blueshifts and vibrational predissociation lifetimes measured for He-I 2 ͑B , Ј͒ in the range Ј= 10-67 of I 2 vibrational excitations. In particular, the accuracy achieved in the description of the experimental data for high Ј levels is attributed to the three-body interaction term included in the potential. The behavior of the potential surface with the I-I separation is analyzed and correlated with the experimental findings.
The Journal of Chemical Physics, 2005