Florent Gadea - Academia.edu (original) (raw)
Papers by Florent Gadea
International Journal of Quantum Chemistry
The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 ... more The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 molecular states dissociating up to Sr2+ + H− using an ab initio approach. The ab initio formalism is based on large basis sets, nonempirical atomic pseudopotential for strontium core, correlation treatment for core valence through the effective core polarization potentials and for valence through full valence configuration interaction. Our theoretical molecular constants match published values very well and a large amount of new results is produced. Unusual potential shapes are found in 1Σ+ states often caused by avoided crossing series between them and imprinted by the ionic state Sr2+H−. The high potential energy curves suggest, it is possible to form H− or at least to neutralize H+ in collisions with strontium. © 2014 Wiley Periodicals, Inc.
Pressure broadening by molecular hydrogen and helium is one of the major broadening mechanism in ... more Pressure broadening by molecular hydrogen and helium is one of the major broadening mechanism in the atmosphere of brown dwarfs. He(1 ^1S)-He(2 ^1P) collisional line profiles are determined in a unified theory of spectral line broadening using very recent ab initio potential energies. Results are reported for the conditions prevailing in brown dwarf atmospheres.
Theoretical Chemistry Accounts, 2006
Ab initio calculations were performed for LiH using a pseudopotential approach with CPP correctio... more Ab initio calculations were performed for LiH using a pseudopotential approach with CPP corrections and huge basis sets on both atoms. A wide range of 1,3Σ+ electronic adiabatic states have been investigated, from the ground state up to those dissociating into Li(5p)+H. Permanent and transition electric dipole moments are also considered for the first few excited states. Comparison with experiments
Journal of Molecular Structure: THEOCHEM, 2006
The evaluation of the first and second derivative of the non adiabatic coupling between the sever... more The evaluation of the first and second derivative of the non adiabatic coupling between the several 1 R + adiabatic states of LiH, RbH and CsH molecules, is considered from accurate diabatic and adiabatic data. Such derivatives of the electronic wave function are determined through a numerical differentiation of the rotational matrix connecting the diabatic and adiabatic representations. The first as well as the second derivative presents many peaks, related to ionic-neutral and neutral-neutral coupling between the 1 R + states. Such radial coupling has been exploited to calculate the first adiabatic correction, which corresponds to the diagonal term of the second derivative divided by the reduced mass, for the ground and some excited states of the three molecules. The second adiabatic correction has been determined using the Virial theorem.
The Journal of Chemical Physics, 2014
Collision cross sections and transport coefficients are calculated for Ar + ions, in the ground s... more Collision cross sections and transport coefficients are calculated for Ar + ions, in the ground state 2 P 3/2 and in the metastable state 2 P 1/2 , colliding with their parent gas. Differential and integral collision cross sections are obtained using a numerical integration of the nuclear Schrödinger equation for several published interaction potentials. The Cohen-Schneider semi-empirical model is used for the inclusion of the spin-orbit interaction. The corresponding differential collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients for each initial ion state over a wide range of reduced electric field. Ion swarm data results are then compared with available experimental data for different proportions of ions in each state. This allows us to identify the most reliable interaction potential which reproduces ion transport coefficients falling within the experimental error bars. Such ion transport data will be used in electrohydrodynamic and chemical kinetic models of the low temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.
Chemical Physics, 2007
Accurate energy ab initio calculations have been performed for three lowest electronic states of ... more Accurate energy ab initio calculations have been performed for three lowest electronic states of He3+ using the internally contracted multireference configuration interaction (icMRCI) method and an augmented correlation-consistent basis set of atomic orbitals. A broad range of He3+ geometries has been considered and the calculated energies have been represented analytically. The present results are thoroughly checked in comparison with data
Theoretical Chemistry Accounts, 2009
The accuracy of the diatomics-in-molecules (DIM) model for the krypton ionic trimer is examined i... more The accuracy of the diatomics-in-molecules (DIM) model for the krypton ionic trimer is examined in a series of ab initio calculations. In the C2v symmetry, the ground states of irreducible representations B2 and A1 were calculated using partially spin restricted open-shell coupled cluster method with perturbative triple connections (RHF-RCCSD-T), the relativistic effective core potential (RECP) and an extended basis set
The Journal of Physical Chemistry A, 2002
ABSTRACT
The Journal of Physical Chemistry A, 2006
Unimolecular dissociation of neutral and charged argon clusters is theoretically investigated in ... more Unimolecular dissociation of neutral and charged argon clusters is theoretically investigated in the context of calorimetric measurements. The temperature of the product cluster is estimated from the distribution of the translational kinetic energy released (KER), assumed to have the form f(epsilon) approximately epsilon(alpha) exp(-epsilon/k(B)T). Phase space theory (PST) in its orbiting transition state (OTS) version is validated by comparing its predictions to the results of large-scale molecular dynamics simulations. The temperatures estimated from the KER distributions are seen to be generally lower than the actual microcanonical temperature computed from independent Monte Carlo simulations of the product cluster at thermal equilibrium. On the basis of these deviations, the various approximations leading from the rigorous PST/OTS treatment to the assumed exponential form are critically discussed. In the case of Ar(n)(+) clusters, the use of a quantum diatomic-in-molecules Hamiltonian constructed from recent ab initio calculations reveals some possible inadequacies of the 1/r(4) ion/dipole interaction at intermediate distances due to some residual charge transfer.
Physical Review A, 2006
... Electronic address: osman.atabek@ppm.u-psud.fr †Also at UFR de Physique ... We have followed ... more ... Electronic address: osman.atabek@ppm.u-psud.fr †Also at UFR de Physique ... We have followed in this way the five lowest diabatic energies. For vdiab=0,1,3, and 4 the width starts, as expected, as a linear function of the intensity, then passes through a maxi-mum. ...
Physical Review A, 2009
Semiclassical mean-field dynamics approach is used in combination with diatomics-in-molecules met... more Semiclassical mean-field dynamics approach is used in combination with diatomics-in-molecules methods to study photodissociation of ionized trimers of argon, krypton, and xenon. The dynamics of photodissociation is analyzed in terms of the kinetic energy distribution of ionic and neutral fragments, fragmentation patterns, and fragmentation times. Particular attention is paid to the effect of the spin-orbit coupling and clusters temperature. Theoretical
Journal of Physics: Conference Series, 2012
ABSTRACT This study of the self-broadening of the 728 nm He line is performed in order to establi... more ABSTRACT This study of the self-broadening of the 728 nm He line is performed in order to establish similarities and differences to the self-broadening of the triplet 3s-2p line at 706 nm. In a previous work we presented the first calculations of He-He collisional profiles at 706nm due to the triplet 3s-2p transition in a unified line shape semi-classical theory using ab-initio molecular potentials. The excellent agreement between experimental and theoretical determinations of the near wing of the line profiles established the accuracy of the interaction potentials. New ab-initio potentials for the singlet 3s-2p transitions allow us to extend our previous study to the line at 728 nm.
Journal of Computational Chemistry, 2013
For all states dissociating below the ionic limit Li(-) Rb(+) , we perform a diabatic study for (... more For all states dissociating below the ionic limit Li(-) Rb(+) , we perform a diabatic study for (1) Σ(+) electronic states dissociating into Rb (5s, 5p, 4d, 6s, 6p, 5d, 7s, 4f) + Li (2s, 2p, 3s). Furthermore, we present the diabatic results for the 1-11 (3) σ, 1-8 (1,3) Π, and 1-4 (1,3) Δ states. The present calculations on the RbLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on ab-initio pseudopotential, core polarization potential operators for the core-valence correlation and full valence configuration interaction approaches, combined to an efficient diabatization procedure. For the low-lying states, diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the (1) Σ(+) adiabatic states. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 2 (1) Σ(+) excited states for the first time. In addition to the bound-bound contribution, the bound-free term has been evaluated using the Franck-Condon approximation and also exactly added to the total radiative lifetime.
The Journal of Chemical Physics, 2007
Rovibrational spectra of Ar 3 are computed for total angular momenta up to J = 6 using row-orthon... more Rovibrational spectra of Ar 3 are computed for total angular momenta up to J = 6 using row-orthonormal hyperspherical coordinates and an expansion of the wave function on hyperspherical harmonics. The sensitivity of the spectra to the two-body potential and to the three-body corrections is analyzed. First, the best available semiempirical pair potential ͑HFDID1͒ is compared with our recent ab initio two-body potential. The ab initio vibrational energies are typically 1-2 cm −1 higher than the semiempirical ones, which is related to the slightly larger dissociation energy of the semiempirical potential. Then, the Axilrod-Teller asymptotic expansion of the three-body correction is compared with our newly developed ab initio three-body potential. The difference is found smaller than 0.3 cm −1 . In addition, we define approximate quantum numbers to describe the vibration and rotation of the system. The vibration is represented by a hyper-radial mode and a two-degree-of-freedom hyperangular mode, including a vibrational angular momentum defined in an Eckart frame. The rotation is described by the total angular momentum quantum number, its projection on the axis perpendicular to the molecular plane, and a hyperangular internal momentum quantum number, related to the vibrational angular momentum by a transformation between Eckart and principal-axes-of-inertia frames. These quantum numbers provide a qualitative understanding of the spectra and, in particular, of the impact of the nuclear permutational symmetry of the system ͑bosonic with zero nuclear spin͒. Rotational constants are extracted from the spectra and are shown to be accurate only for the ground hyperangular mode. Downloaded 04 May 2007 to 130.120.230.129. Redistribution subject to AIP license or copyright, see http://jcp.aip.org/jcp/copyright.jsp M J d D ͑⍀͒.
The Journal of Chemical Physics, 2006
The dynamics of ionic rare-gas trimers (Ar(3) (+), Kr(3) (+), and Xe(3) (+)) produced by a sudden... more The dynamics of ionic rare-gas trimers (Ar(3) (+), Kr(3) (+), and Xe(3) (+)) produced by a sudden ionization of neutral precursors is investigated theoretically with a hybrid classical-quantum method for solving the equations of motion governed by a Hamiltonian obtained from a previously tested diatomics-in-molecules model. Initial conditions are selected with Monte Carlo sampling. Two possibilities for generating the initial electronic state are considered: diabatic (local) and adiabatic (delocalized). The dynamics generally leads to fragmentation, producing either monomer ions or dimer ions in a relatively short time; however, a large number of long-lived metastable trimer ions are also seen in some cases. We have analyzed the dynamics with respect to the fraction of monomer ions produced, the distribution of the kinetic energy of the products, and the distribution of fragmentation times of the trimers. Initial diabatic ionization is associated with much faster fragmentation than adiabatic ionization. Spin-orbit coupling plays an important role in the fragmentation dynamics.
The Journal of Chemical Physics, 2006
The dynamics and thermodynamics of small Ar n + clusters, n = 3, 6, and 9, are investigated using... more The dynamics and thermodynamics of small Ar n + clusters, n = 3, 6, and 9, are investigated using molecular dynamics ͑MD͒ and exchange Monte Carlo ͑MC͒ simulations. A diatomic-in-molecule Hamiltonian provides an accurate model for the electronic ground state potential energy surface. The microcanonical caloric curves calculated from MD and MC methods are shown to agree with each other, provided that the rigorous conservation of angular momentum is accounted for in the phase space density of the MC simulations. The previously proposed projective partition of the kinetic energy is used to assist MD simulations in interpreting the cluster dynamics in terms of inertial, internal, and external modes. The thermal behavior is correlated with the nature of the charged core in the cluster by computing a dedicated charge localization order parameter. We also perform systematic quenches to establish a connection with the various isomers. We find that the Ar 3 + cluster is very stable in its linear ground state geometry up to about 300 K, and then isomerizes to a T-shaped isomer in which a quasineutral atom lies around a charged dimer. In Ar 6 + and Ar 9 + , the covalent trimer core is solvated by neutral atoms, and the weakly bound solvent shell melts at much lower energies, occasionally leading to a tetramer or pentamer core with weakly charged extremities. At high energies the core itself becomes metastable and the cluster transforms into Ar 2 + solvated by a fluid of neutral argon atoms.
The Journal of Chemical Physics, 2010
Photodissociation of the ionized argon pentamer, Ar 5 + , is studied using an extended diatomics-... more Photodissociation of the ionized argon pentamer, Ar 5 + , is studied using an extended diatomics-inmolecules interaction model with the inclusion of the spin-orbit coupling and various dynamical approaches. A thorough comparison with the experimental data available in the literature is presented, including photofragment abundances and their kinetic and internal energy distributions. New predictions are reported for ultraviolet photoexcitation energies, a range that has not been studied before either experimentally or theoretically.
The Journal of Chemical Physics, 2009
A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics... more A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics (mixing classical and quantum approach) and applied to the postionization of rare-gas trimers. There was an important disagreement between trajectory surface hopping (TSH) or mean field (MF) approaches and the experimental results; noteworthy, with the new method qualitative and almost quantitative agreement is found for the fragmentation ratios of ionic monomers and dimers. For the first time in the theory as in the experiment, the dimers prevail for argon while monomers strongly dominate for the heavier rare gases, krypton and xenon. A new compromise between MF and TSH approaches is proposed and the new method is found quite robust with results not too sensitive to various possible implementations.
The Journal of Chemical Physics, 2008
We have computed the vibrational spectrum of the helium ionized trimer He(3)(+) using three diffe... more We have computed the vibrational spectrum of the helium ionized trimer He(3)(+) using three different potential energy surfaces [D. T. Chang and G. L. Gellene, J. Chem. Phys. 119, 4694 (2003); E. Scifoni et al., ibid. 125, 164304 (2006); I. Paidarova et al., Chem. Phys. 342, 64 (2007)]. Differences in the details of these potential energy surfaces induce discrepancies between bound state energies of the order of 0.01 eV. The effects of the geometric phase induced by the conical intersection between the ground electronic potential energy surface and the first excited one are studied by computing vibrational spectra with and without this phase. The six lowest vibrational bound states are negligibly affected by the geometric phase. Indeed, they correspond to wavefunctions localized in the vicinity of the linear symmetric configurations and can be assigned well defined vibrational quantum numbers. On the other hand, higher excited states are delocalized, cannot be assigned definite vibrational quantum numbers, and the geometric phase shifts their energies by approximately 0.005 eV.
International Journal of Quantum Chemistry, 2014
A wide adiabatic study is performed for NaRb molecule, involving 15 1 R 1 electronic states inclu... more A wide adiabatic study is performed for NaRb molecule, involving 15 1 R 1 electronic states including the ionic state Na 2 Rb 1 , as well as 14 3 R 1 , 1-9 1,3 P, and 1-5 1,3 D states. This investigation is performed using an ab initio approach which involves the effective core potential, the core polarization potential with l-dependent cut-off functions. The NaRb system has been treated as a two-electron system and the full valence configuration interaction is easily achieved. The spectroscopic constants R e , D e , T e , x e , x e x e , B e , and D 0 for all these states are derived. We have also computed the vibrational levels as well their spacing for different values of J. In addition, permanent and transition dipole moments are determined and analyzed. The Dunham coefficients have been used to perform experimental spacing to compare directly with our results. The present calculations on NaRb extend previous theoretical works to numerous electronic excited states in the various symmetries.
International Journal of Quantum Chemistry
The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 ... more The potentials, spectroscopic properties and electric dipole moments of SrH+ are computed for 63 molecular states dissociating up to Sr2+ + H− using an ab initio approach. The ab initio formalism is based on large basis sets, nonempirical atomic pseudopotential for strontium core, correlation treatment for core valence through the effective core polarization potentials and for valence through full valence configuration interaction. Our theoretical molecular constants match published values very well and a large amount of new results is produced. Unusual potential shapes are found in 1Σ+ states often caused by avoided crossing series between them and imprinted by the ionic state Sr2+H−. The high potential energy curves suggest, it is possible to form H− or at least to neutralize H+ in collisions with strontium. © 2014 Wiley Periodicals, Inc.
Pressure broadening by molecular hydrogen and helium is one of the major broadening mechanism in ... more Pressure broadening by molecular hydrogen and helium is one of the major broadening mechanism in the atmosphere of brown dwarfs. He(1 ^1S)-He(2 ^1P) collisional line profiles are determined in a unified theory of spectral line broadening using very recent ab initio potential energies. Results are reported for the conditions prevailing in brown dwarf atmospheres.
Theoretical Chemistry Accounts, 2006
Ab initio calculations were performed for LiH using a pseudopotential approach with CPP correctio... more Ab initio calculations were performed for LiH using a pseudopotential approach with CPP corrections and huge basis sets on both atoms. A wide range of 1,3Σ+ electronic adiabatic states have been investigated, from the ground state up to those dissociating into Li(5p)+H. Permanent and transition electric dipole moments are also considered for the first few excited states. Comparison with experiments
Journal of Molecular Structure: THEOCHEM, 2006
The evaluation of the first and second derivative of the non adiabatic coupling between the sever... more The evaluation of the first and second derivative of the non adiabatic coupling between the several 1 R + adiabatic states of LiH, RbH and CsH molecules, is considered from accurate diabatic and adiabatic data. Such derivatives of the electronic wave function are determined through a numerical differentiation of the rotational matrix connecting the diabatic and adiabatic representations. The first as well as the second derivative presents many peaks, related to ionic-neutral and neutral-neutral coupling between the 1 R + states. Such radial coupling has been exploited to calculate the first adiabatic correction, which corresponds to the diagonal term of the second derivative divided by the reduced mass, for the ground and some excited states of the three molecules. The second adiabatic correction has been determined using the Virial theorem.
The Journal of Chemical Physics, 2014
Collision cross sections and transport coefficients are calculated for Ar + ions, in the ground s... more Collision cross sections and transport coefficients are calculated for Ar + ions, in the ground state 2 P 3/2 and in the metastable state 2 P 1/2 , colliding with their parent gas. Differential and integral collision cross sections are obtained using a numerical integration of the nuclear Schrödinger equation for several published interaction potentials. The Cohen-Schneider semi-empirical model is used for the inclusion of the spin-orbit interaction. The corresponding differential collision cross sections are then used in an optimized Monte Carlo code to calculate the ion transport coefficients for each initial ion state over a wide range of reduced electric field. Ion swarm data results are then compared with available experimental data for different proportions of ions in each state. This allows us to identify the most reliable interaction potential which reproduces ion transport coefficients falling within the experimental error bars. Such ion transport data will be used in electrohydrodynamic and chemical kinetic models of the low temperature plasma jet to quantify and to tune the active species production for a better use in biomedical applications.
Chemical Physics, 2007
Accurate energy ab initio calculations have been performed for three lowest electronic states of ... more Accurate energy ab initio calculations have been performed for three lowest electronic states of He3+ using the internally contracted multireference configuration interaction (icMRCI) method and an augmented correlation-consistent basis set of atomic orbitals. A broad range of He3+ geometries has been considered and the calculated energies have been represented analytically. The present results are thoroughly checked in comparison with data
Theoretical Chemistry Accounts, 2009
The accuracy of the diatomics-in-molecules (DIM) model for the krypton ionic trimer is examined i... more The accuracy of the diatomics-in-molecules (DIM) model for the krypton ionic trimer is examined in a series of ab initio calculations. In the C2v symmetry, the ground states of irreducible representations B2 and A1 were calculated using partially spin restricted open-shell coupled cluster method with perturbative triple connections (RHF-RCCSD-T), the relativistic effective core potential (RECP) and an extended basis set
The Journal of Physical Chemistry A, 2002
ABSTRACT
The Journal of Physical Chemistry A, 2006
Unimolecular dissociation of neutral and charged argon clusters is theoretically investigated in ... more Unimolecular dissociation of neutral and charged argon clusters is theoretically investigated in the context of calorimetric measurements. The temperature of the product cluster is estimated from the distribution of the translational kinetic energy released (KER), assumed to have the form f(epsilon) approximately epsilon(alpha) exp(-epsilon/k(B)T). Phase space theory (PST) in its orbiting transition state (OTS) version is validated by comparing its predictions to the results of large-scale molecular dynamics simulations. The temperatures estimated from the KER distributions are seen to be generally lower than the actual microcanonical temperature computed from independent Monte Carlo simulations of the product cluster at thermal equilibrium. On the basis of these deviations, the various approximations leading from the rigorous PST/OTS treatment to the assumed exponential form are critically discussed. In the case of Ar(n)(+) clusters, the use of a quantum diatomic-in-molecules Hamiltonian constructed from recent ab initio calculations reveals some possible inadequacies of the 1/r(4) ion/dipole interaction at intermediate distances due to some residual charge transfer.
Physical Review A, 2006
... Electronic address: osman.atabek@ppm.u-psud.fr †Also at UFR de Physique ... We have followed ... more ... Electronic address: osman.atabek@ppm.u-psud.fr †Also at UFR de Physique ... We have followed in this way the five lowest diabatic energies. For vdiab=0,1,3, and 4 the width starts, as expected, as a linear function of the intensity, then passes through a maxi-mum. ...
Physical Review A, 2009
Semiclassical mean-field dynamics approach is used in combination with diatomics-in-molecules met... more Semiclassical mean-field dynamics approach is used in combination with diatomics-in-molecules methods to study photodissociation of ionized trimers of argon, krypton, and xenon. The dynamics of photodissociation is analyzed in terms of the kinetic energy distribution of ionic and neutral fragments, fragmentation patterns, and fragmentation times. Particular attention is paid to the effect of the spin-orbit coupling and clusters temperature. Theoretical
Journal of Physics: Conference Series, 2012
ABSTRACT This study of the self-broadening of the 728 nm He line is performed in order to establi... more ABSTRACT This study of the self-broadening of the 728 nm He line is performed in order to establish similarities and differences to the self-broadening of the triplet 3s-2p line at 706 nm. In a previous work we presented the first calculations of He-He collisional profiles at 706nm due to the triplet 3s-2p transition in a unified line shape semi-classical theory using ab-initio molecular potentials. The excellent agreement between experimental and theoretical determinations of the near wing of the line profiles established the accuracy of the interaction potentials. New ab-initio potentials for the singlet 3s-2p transitions allow us to extend our previous study to the line at 728 nm.
Journal of Computational Chemistry, 2013
For all states dissociating below the ionic limit Li(-) Rb(+) , we perform a diabatic study for (... more For all states dissociating below the ionic limit Li(-) Rb(+) , we perform a diabatic study for (1) Σ(+) electronic states dissociating into Rb (5s, 5p, 4d, 6s, 6p, 5d, 7s, 4f) + Li (2s, 2p, 3s). Furthermore, we present the diabatic results for the 1-11 (3) σ, 1-8 (1,3) Π, and 1-4 (1,3) Δ states. The present calculations on the RbLi molecule are complementary to previous theoretical work on this system, including recently observed electronic states that had not been calculated previously. The calculations rely on ab-initio pseudopotential, core polarization potential operators for the core-valence correlation and full valence configuration interaction approaches, combined to an efficient diabatization procedure. For the low-lying states, diabatic potentials and permanent dipole moments are analyzed, revealing the strong imprint of the ionic state in the (1) Σ(+) adiabatic states. The transition dipole moment is used to evaluate the radiative lifetimes of the vibrational levels trapped in the 2 (1) Σ(+) excited states for the first time. In addition to the bound-bound contribution, the bound-free term has been evaluated using the Franck-Condon approximation and also exactly added to the total radiative lifetime.
The Journal of Chemical Physics, 2007
Rovibrational spectra of Ar 3 are computed for total angular momenta up to J = 6 using row-orthon... more Rovibrational spectra of Ar 3 are computed for total angular momenta up to J = 6 using row-orthonormal hyperspherical coordinates and an expansion of the wave function on hyperspherical harmonics. The sensitivity of the spectra to the two-body potential and to the three-body corrections is analyzed. First, the best available semiempirical pair potential ͑HFDID1͒ is compared with our recent ab initio two-body potential. The ab initio vibrational energies are typically 1-2 cm −1 higher than the semiempirical ones, which is related to the slightly larger dissociation energy of the semiempirical potential. Then, the Axilrod-Teller asymptotic expansion of the three-body correction is compared with our newly developed ab initio three-body potential. The difference is found smaller than 0.3 cm −1 . In addition, we define approximate quantum numbers to describe the vibration and rotation of the system. The vibration is represented by a hyper-radial mode and a two-degree-of-freedom hyperangular mode, including a vibrational angular momentum defined in an Eckart frame. The rotation is described by the total angular momentum quantum number, its projection on the axis perpendicular to the molecular plane, and a hyperangular internal momentum quantum number, related to the vibrational angular momentum by a transformation between Eckart and principal-axes-of-inertia frames. These quantum numbers provide a qualitative understanding of the spectra and, in particular, of the impact of the nuclear permutational symmetry of the system ͑bosonic with zero nuclear spin͒. Rotational constants are extracted from the spectra and are shown to be accurate only for the ground hyperangular mode. Downloaded 04 May 2007 to 130.120.230.129. Redistribution subject to AIP license or copyright, see http://jcp.aip.org/jcp/copyright.jsp M J d D ͑⍀͒.
The Journal of Chemical Physics, 2006
The dynamics of ionic rare-gas trimers (Ar(3) (+), Kr(3) (+), and Xe(3) (+)) produced by a sudden... more The dynamics of ionic rare-gas trimers (Ar(3) (+), Kr(3) (+), and Xe(3) (+)) produced by a sudden ionization of neutral precursors is investigated theoretically with a hybrid classical-quantum method for solving the equations of motion governed by a Hamiltonian obtained from a previously tested diatomics-in-molecules model. Initial conditions are selected with Monte Carlo sampling. Two possibilities for generating the initial electronic state are considered: diabatic (local) and adiabatic (delocalized). The dynamics generally leads to fragmentation, producing either monomer ions or dimer ions in a relatively short time; however, a large number of long-lived metastable trimer ions are also seen in some cases. We have analyzed the dynamics with respect to the fraction of monomer ions produced, the distribution of the kinetic energy of the products, and the distribution of fragmentation times of the trimers. Initial diabatic ionization is associated with much faster fragmentation than adiabatic ionization. Spin-orbit coupling plays an important role in the fragmentation dynamics.
The Journal of Chemical Physics, 2006
The dynamics and thermodynamics of small Ar n + clusters, n = 3, 6, and 9, are investigated using... more The dynamics and thermodynamics of small Ar n + clusters, n = 3, 6, and 9, are investigated using molecular dynamics ͑MD͒ and exchange Monte Carlo ͑MC͒ simulations. A diatomic-in-molecule Hamiltonian provides an accurate model for the electronic ground state potential energy surface. The microcanonical caloric curves calculated from MD and MC methods are shown to agree with each other, provided that the rigorous conservation of angular momentum is accounted for in the phase space density of the MC simulations. The previously proposed projective partition of the kinetic energy is used to assist MD simulations in interpreting the cluster dynamics in terms of inertial, internal, and external modes. The thermal behavior is correlated with the nature of the charged core in the cluster by computing a dedicated charge localization order parameter. We also perform systematic quenches to establish a connection with the various isomers. We find that the Ar 3 + cluster is very stable in its linear ground state geometry up to about 300 K, and then isomerizes to a T-shaped isomer in which a quasineutral atom lies around a charged dimer. In Ar 6 + and Ar 9 + , the covalent trimer core is solvated by neutral atoms, and the weakly bound solvent shell melts at much lower energies, occasionally leading to a tetramer or pentamer core with weakly charged extremities. At high energies the core itself becomes metastable and the cluster transforms into Ar 2 + solvated by a fluid of neutral argon atoms.
The Journal of Chemical Physics, 2010
Photodissociation of the ionized argon pentamer, Ar 5 + , is studied using an extended diatomics-... more Photodissociation of the ionized argon pentamer, Ar 5 + , is studied using an extended diatomics-inmolecules interaction model with the inclusion of the spin-orbit coupling and various dynamical approaches. A thorough comparison with the experimental data available in the literature is presented, including photofragment abundances and their kinetic and internal energy distributions. New predictions are reported for ultraviolet photoexcitation energies, a range that has not been studied before either experimentally or theoretically.
The Journal of Chemical Physics, 2009
A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics... more A new theoretical approach is presented for the general treatment of nonadiabatic hybrid dynamics (mixing classical and quantum approach) and applied to the postionization of rare-gas trimers. There was an important disagreement between trajectory surface hopping (TSH) or mean field (MF) approaches and the experimental results; noteworthy, with the new method qualitative and almost quantitative agreement is found for the fragmentation ratios of ionic monomers and dimers. For the first time in the theory as in the experiment, the dimers prevail for argon while monomers strongly dominate for the heavier rare gases, krypton and xenon. A new compromise between MF and TSH approaches is proposed and the new method is found quite robust with results not too sensitive to various possible implementations.
The Journal of Chemical Physics, 2008
We have computed the vibrational spectrum of the helium ionized trimer He(3)(+) using three diffe... more We have computed the vibrational spectrum of the helium ionized trimer He(3)(+) using three different potential energy surfaces [D. T. Chang and G. L. Gellene, J. Chem. Phys. 119, 4694 (2003); E. Scifoni et al., ibid. 125, 164304 (2006); I. Paidarova et al., Chem. Phys. 342, 64 (2007)]. Differences in the details of these potential energy surfaces induce discrepancies between bound state energies of the order of 0.01 eV. The effects of the geometric phase induced by the conical intersection between the ground electronic potential energy surface and the first excited one are studied by computing vibrational spectra with and without this phase. The six lowest vibrational bound states are negligibly affected by the geometric phase. Indeed, they correspond to wavefunctions localized in the vicinity of the linear symmetric configurations and can be assigned well defined vibrational quantum numbers. On the other hand, higher excited states are delocalized, cannot be assigned definite vibrational quantum numbers, and the geometric phase shifts their energies by approximately 0.005 eV.
International Journal of Quantum Chemistry, 2014
A wide adiabatic study is performed for NaRb molecule, involving 15 1 R 1 electronic states inclu... more A wide adiabatic study is performed for NaRb molecule, involving 15 1 R 1 electronic states including the ionic state Na 2 Rb 1 , as well as 14 3 R 1 , 1-9 1,3 P, and 1-5 1,3 D states. This investigation is performed using an ab initio approach which involves the effective core potential, the core polarization potential with l-dependent cut-off functions. The NaRb system has been treated as a two-electron system and the full valence configuration interaction is easily achieved. The spectroscopic constants R e , D e , T e , x e , x e x e , B e , and D 0 for all these states are derived. We have also computed the vibrational levels as well their spacing for different values of J. In addition, permanent and transition dipole moments are determined and analyzed. The Dunham coefficients have been used to perform experimental spacing to compare directly with our results. The present calculations on NaRb extend previous theoretical works to numerous electronic excited states in the various symmetries.