Wave packet study of the Ar–HBr photolysis: Stereodynamical effects

7 pages, 6 figures.The ultraviolet photolysis of Ar–HBr(v = 1) is studied through wave packet dynamics simulations, focusing on the fragmentation pathway Ar–HBr + H + Ar–Br. Photolysis starts from two initial states of Ar–HBr(v = 1) with a different angular shape, namely the ground and the first excited van der Waals (vdW) states, corresponding to the Ar–H–Br and Ar–Br–H isomers, respectively. It is found that the yield of Ar–Br radical products is substantially higher for the initial excited vdW state of the cluster, where H dissociation is less hindered. In addition, the yield of radical formation is much higher in the Ar–HBr(v = 1) photolysis than that previously found in the Ar–HCl(v = 0) case, even for the ground vdW state, where the initial angular distribution of both clusters is similar. Another unexpected difference is that Ar–HCl(v = 0) photolysis exhibits strong manifestations of quantum interference, while these effects are much weaker in Ar–HBr(v = 1). A lower probability of the first collision between the recoiling hydrogen and the Ar atom in the case of Ar–HBr(v = 1), due to geometrical differences between its initial state and that of Ar–HCl(v = 0), is suggested to explain the different photolysis behavior of both clusters. The implications of the present findings in the photolysis of other related precursor clusters are discussed.This work was supported by C.I.C.Y.T. (Ministerio de Ciencia y Tegnología), Spain, Grant No. BFM-2001-2179, and by the European network TMR, Grant No. HPRN-CT- 1999-00005.Peer reviewe

Spectroscopy of weakly-bound complexes in highly excited electronic states: the HeI2(E3g) ion-pair state

1 pag.; 2 figs. XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013) IOP PublishingThe study of electronically excited van der Waals (vdW) systems presents a challenge for the theory of intermolecular interactions, and here we show how far ab initio computations can go. We found that the interaction energies for such electronically excited systems can indeed be determined, providing a reliable and accurate description for the E state potential of the HeI2, that in combination with the ground X and electronic excited B state of the complex, is useful to model experimental data related with potential minima and also predict higher vibrational vdW states.Peer Reviewe

Confining CO2 inside the nanocavities of the sI clathrate: a quantum dynamics study

ICPEAC 2015, Toledo, Spain on 22 –28 July 2015; http://www.icpeac2015.com/Clathrate hydrates have been found to occur naturally, and have been extensively studied due to their important industrial applications, such as the storage of the CO2 from the atmosphere and control climate change. Thus, quantitative understanding of physical and chemical properties, as well as the factors that control the formation of CO2 hydrates, on both macroscopic and microscopic levels is essential in several areas of physical science.Peer Reviewe

Modeling the water-halide ion interactions

1 pág.; 1 fig.; XXIX International Conference on Photonic, Electronic, and Atomic Collisions (ICPEAC2015); Open Access funded by Creative Commons Atribution Licence 3.0Ions play an important role in many heterogeneous processes, and understanding specific ion effects is a key point in studying solvation mechanisms in liquids as well as reactivity of aerosol particles. In this regard, a crucial issue to be resolved is the extent to which ions influence the structural and dynamical properties of the surrounding hydrogen bond network and, at the same time, to provide a direct molecular-level interpretation of the experimental measurements.Peer Reviewe

Spectral simulations and vibrational dynamics of the fluxional H+5 cationand its isotopologues: signatures of the shared-proton motions

1 pag.; 2 figs. PACS 33.20.Tp Vibrational analysis; 34.50.-s Scattering of atoms and molecules; 31.15.-p Calculations and mathematical techniques in atomic and molecular physics; 33.15.Mt Rotation, vibration, and vibration-rotation constants. XXVIII International Conference on Photonic, Electronic and Atomic Collisions (ICPEAC 2013) IOP Publishing.The recent increased interest on research studies of the H+5 cation, and its isotopologues, is due to the postulation for their presence, although still not detected, in the interstellar medium. There is no doubt, particularly in the light of the recent laboratory observations, that the spectroscopy of these systems is also a great challenge for the theorists. Thus, we report the first fully converged coupled anharmonic quantum study on vibrational dynamics of these highly fluxional cations, providing important information on their spectroscopy in a rigorous manner, and open perspectives for further investigations. Published under licence by IOP Publishing LtdPeer Reviewe

Full-dimensional (15-dimensional) ab initio analytical potential energy surface for the H 7 + cluster

Full-dimensional ab initio potential energy surface is constructed for the H7+ cluster. The surface is a fit to roughly 160 000 interaction energies obtained with second-order MöllerPlesset perturbation theory and the cc-pVQZ basis set, using the invariant polynomial method [B. J. Braams and J. M. Bowman, Int. Rev. Phys. Chem. 28, 577 (2009)10.1080/01442350903234923]. We employ permutationally invariant basis functions in Morse-type variables for all the internuclear distances to incorporate permutational symmetry with respect to interchange of H atoms into the representation of the surface. We describe how different configurations are selected in order to create the database of the interaction energies for the linear least squares fitting procedure. The root-mean-square error of the fit is 170 cm -1 for the entire data set. The surface dissociates correctly to the H5+ H 2 fragments. A detailed analysis of its topology, as well as comparison with additional ab initio calculations, including harmonic frequencies, verify the quality and accuracy of the parameterized potential. This is the first attempt to present an analytical representation of the 15-dimensional surface of the H7+ cluster for carrying out dynamics studies. © 2012 American Institute of Physics.. R.P. acknowledges financial support by Ministerio de Ciencia e Innovacion, Spain, Grant No. FIS2010-18132, FIS2011-29596-C02-01 and European Cooperation in Scientific and Technical Research (COST) Action CM1002 (CODECS). P.B. acknowledges a postdoctoral fellowship from the Ramón Areces Foundation, Spain. J.M.B. and Y.W. thank the National Science Foundation (CHE-1145227) for financial support.Peer Reviewe

Theoretical characterization of intermolecular vibrational states through the multi-configuration time dependent Hartree approach: The He 2,3ICl clusters

Benchmark, full-dimensional calculations on the ground and excited vibrational states for the tetra-, and penta-atomic weakly bound He 2,3ICl complexes are reported. The representation of the potential energy surfaces includes three-body HeICl potentials parameterized to coupled-cluster singles, doubles, and perturbative triples ab initio data. These terms are important in accurately describing the interactions of such highly floppy systems. The corresponding 6D/9D computations are performed with the multi-configuration time dependent Hartree method, using natural potential fits, and a mode combination scheme to optimize the computational effort in the improved relaxation calculations. For these complexes several low-lying vibrational states are computed, and their binding energies and radial/angular probability density distributions are obtained. We found various isomers which are assigned to different structural models related with combinations of the triatomic isomers, like linear, T-shaped, and antilinear ones. Comparison of these results with recent experimental data is presented, and the quantitative deviations found with respect to the experiment are discussed. © 2011 American Institute of Physics.The authors thank to Centro de Calculo (IFF), CTI (CSIC), and CESGA for allocation of computer time. This work has been supported by DGICYT, Spain, Grant No. FIS2010-18132 and the COST Action CM1002 (CODECS).Peer Reviewe

Ab initio ground state potential energy surfaces for Rg–Br2 (Rg = He, Ne, Ar) complexes

6 pages, 3 figures, 5 tables.-- PACS: 31.15.Ar; 31.15.Dv; 33.15.Bh; 33.15.MtHigh-level ab initio molecular electronic structure calculations are performed for Rg–Br2 (Rg = He, Ne, Ar) complexes at CCSD(T) (coupled cluster using single and double excitations with a noniterative perturbation treatment of triple excitations) level of theory. Specific augmented correlation consistent basis sets are used for each noble atom (Rg), supplemented with an additional set of bond functions. Effective-core potentials (ECPs), augmented with diffusion (sp) and polarization (3df ) functions, have been employed for the bromine atoms. For all complexes, the CCSD(T) potential energy surfaces (PESs) show double-minimum topology, with wells at both linear and T-shaped configurations; the linear minimum is found to be deeper than the T-shaped one. Vibrational corrections are taken into account for all the complexes and their effects in the stability of the linear and T-shaped conformers are examined. For each complex and each configuration (linear and T-shaped), Re equilibrium intermolecular distances, De and D0 dissociation energies, are evaluated and compared with previous theoretical and/or experimental results.This work has been supported by DGICYT, Spain, Grant No. BCM 2001-2179 and by a European TMR network, Grant No. HPRN-CT-1999-00005. C.C. is indebted to CNPq, Brazil for supporting his postdoctoral at C.S.I.C, Proc. 200688/ 00-6 and R.P. acknowledges a postdoctoral fellowship by MEC, Spain, Ref. No. SB99 N0714831.Peer reviewe

Frequency domain description of Kohlrausch response through a pair of Havriliak-Negami-type functions: An analysis of functional proximity

An approximation to the Fourier transform (FT) of the Kohlrausch function (stretched exponential) with shape parameter 0<β≤1 is presented by using Havriliak-Negami-like functions. Mathematical expressions to fit their parameters α, γ, and τ, as functions of β (0<β≤1 and 1<β<2) are given, which allows a quick identification in the frequency domain of the corresponding shape factor β. Reconstruction via fast Fourier transform of frequency approximants to time domain are shown as good substitutes in short times though biased in long ones (increasing discrepancies as β→1). The method is proposed as a template to commute time and frequency domains when analyzing complex data. Such a strategy facilitates intensive algorithmic search of parameters while adjusting the data of one or several Kohlrausch-Williams-Watts relaxations. © 2011 American Physical Society.This work has been supported by DGICYT, Spain, Grant No. FIS2010-18132.Peer Reviewe

Ab initio vibrational predissociation dynamics of He-I2(B) complex

7 pages, 5 figures, 5 tables.-- PACS nrs.: 31.15.Ar; 31.15.Dv; 33.80.Gj; 33.20.Tp; 33.70.Ca.Three-dimensional quantum mechanical calculations on the vibrational predissociation dynamics of HeI2 B state complex are performed using a potential energy surface accurately fitted to unrestricted open-shell coupled cluster ab initio data, further enabling extrapolation for large I2 bond lengths. A Lanczos iterative method with an optimized complex absorbing potential is used to determine energies and lifetimes of the vibrationally predissociating He,I2(B,v') complex for v' ≤ 26 of I2 vibrational excitations. The calculated predissociating state energies agree with recent experimental results within 0.5 cm−1. This excellent agreement is remarkable since no adjustment was made with respect to the experiments. The present ab initio approach, however, shows its limitations in the fact that the computed lifetimes that are highly sensitive to subtle details of the potential energy surfaces such as anisotropy, are a factor of 1.5 larger than the available experimental data.The Centro de Cálculo (IMAFF), CTI (CSIC), CESGA, and MareNostrum (BSC) are acknowledged for allocation of computer time. One of the authors (A.V.) would like to thank CICYT, Spain for a grant to support his stay at the Laboratoire Collisions, Agrégats, Réactivité. One of the authors (R.P.) acknowledges support by Ramón y Cajal Programme Grant No. PDRYC-2006-001017. This work has been supported by DGICYT, Spain, Grant No. FIS2004-02461 and CSIC-CNRS, Grant No. 2005-FR0031.Peer reviewe