An empirical potential-energy surface for the He–I2(BII3u) van der Waals complex including three-body effects

9 pages, 6 figures, 4 tables.-- PACS: 31.50.-xAn empirical intermolecular potential surface is proposed for the He–I2(B3IIu) 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–I2(B,v') in the range v'=10–67 of I2 vibrational excitations. In particular, the accuracy achieved in the description of the experimental data for high v' 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.This work was supported by C.I.C.Y.T. (Ministerio de Educación y Ciencia ), Spain, Grant No. FIS-2004-02461.Peer reviewe

Weak-field laser phase modulation coherent control of asymptotic photofragment distributions

9 págs.; 5 figs.Coherent control of the asymptotic photofragment state-resolved distributions by means of laser phase modulation in the weak-field limit is demonstrated computationally for a polyatomic molecule. The control scheme proposed applies a pump laser field consisting of two pulses delayed in time. Phase modulation of the spectral bandwidth profile of the laser field is achieved by varying the time delay between the pulses. The underlying equations show that such a phase modulation is effective in order to produce control effects on the asymptotic, long-time limit photofragment distributions only when the bandwidths of the two pulses overlap in a frequency range. The frequency overlap of the pulses gives rise to an interference term which is responsible for the modulation of the spectral profile shape. The magnitude of the range of spectral overlap between the pulses becomes an additional control parameter. The control scheme is illustrated computationally for the asymptotic photofragment state distributions produced from different scenarios of the Ne-Br predissociation. An experimental application of the control scheme is found to be straightforward. © the Owner Societies 2016This work was funded by the Ministerio de Economía y Competitividad (Spain), Grant No. CTQ2015-65033-P, and COST Action program, Grant No. CM1401 and CM1405. The Centro de Supercomputación de Galicia (CESGA, Spain) is acknowledged for the use of its resources.Peer Reviewe

Active control of the lifetime of excited resonance states by means of laser pulses

Quantum control of the lifetime of a system in an excited resonance state is investigated theoretically by creating coherent superpositions of overlapping resonances. This control scheme exploits the quantum interference occurring between the overlapping resonances, which can be controlled by varying the width of the laser pulse that creates the superposition state. The scheme is applied to a realistic model of the Br 2(B)-Ne predissociation decay dynamics through a three-dimensional wave packet method. It is shown that extensive control of the system lifetime is achievable, both enhancing and damping it remarkably. An experimental realization of the control scheme is suggested. © 2012 American Institute of Physics.This work was funded by Ministerio de Ciencia e Innovación, Spain, Grant No. FIS2010-18132, Consolider Ingenio program, Grant No. CSD2007-00013, and COST Action program, Grant No. CM1002.Peer Reviewe

Control of the fragment state distributions produced upon decay of an isolated resonance state

4 págs.; 3 figs.Control of the fragment state distributions produced upon decay of a resonance state is achieved by using a weak laser field consisting of two pulses with a varying time delay between them. It is shown that specific product fragment states can be significantly favored or quenched. The efficiency and flexibility of the control method are found to increase with increasing resonance width. The control scheme is completely independent of the specific system to which it is applied, which makes its applicability universal. AIP Publishing.This work was funded by the Ministerio de Economía y Competitividad, MINECO (Spain), Grant No. CTQ2015- 65033-P, and COST Action program, Grant Nos. CM1401 and CM1405. The Centro de Supercomputación de Galicia (CESGA, Spain) is acknowledged for the use of its resources.Peer Reviewe

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

Unravelling the role of quantum interference in the weak-field laser phase modulation control of photofragment distributions

The postpulse transient phase modulation effects observed on fragment populations are explained in terms of the mechanism of interference between overlapping resonances.</p

A remedy for zero-point energy problems in classical trajectories. A combined semiclassical/clasical molecular dynamics algorithm

A new method is proposed for dealing with difficulties in molecular dynamics (MD) simulations caused by nonpreservation of zero-point energies (ZPE) in classical dynamics. Specifically addressed is a difficulty, for molecules held in weakly bound clusters, of energy flow from the initial ZPE of stiff molecular vibrations into soft cluster modes, causing unphysical dissociation or melting of the cluster. The remedy proposed is a classicallike MD algorithm, which treats the stiff modes by semiclassical Gaussian wave packets and the soft modes by classical dynamics, using the time-dependent self-consistent field (TDSCF) approach to couple the classical and the semiclassical modes. The resulting algorithm is very similar in form to classical MD, is computationally simple, stable, and appears free of unphysical effects. The method is illustrated by test applications to models of the clusters I2He and (HBr)2 in the ground states, which dissociate at the expense of their ZPE classically, but remain stable in the new method. @ 1992 American Institute of PhysicsThis research was supported by the Petroleum Research Fund, administered by the American Chemical Society (Grant No. 2966-AC6 to R.B.G.) and by the Institute for Surface and Interface Science at the University of California, Irvine.Peer Reviewe

Semiclassical Wigner Theory of Photodissociation in Three Dimensions: Shedding Light on Its Basis

14 págs.; 10 figs.; 5 apps.The semiclassical Wigner theory (SCWT) of photodissociation dynamics, initially proposed by Brown and Heller [J. Chem. Phys. 75, 186 (1981)] in order to describe state distributions in the products of direct collinear photodissociations, was recently extended to realistic three-dimensional triatomic processes of the same type [Arbelo-González et al., Phys. Chem. Chem. Phys. 15, 9994 (2013)]. The resulting approach, which takes into account rotational motions in addition to vibrational and translational ones, was applied to a triatomic-like model of methyl iodide photodissociation and its predictions were found to be in nearly quantitative agreement with rigorous quantum results, but at a much lower computational cost, making thereby SCWT a potential tool for the study of polyatomic reaction dynamics. Here, we analyse the main reasons for this agreement by means of an elementary model of fragmentation explicitly dealing with the rotational motion only. We show that our formulation of SCWT makes it a semiclassical approximation to an approximate planar quantum treatment of the dynamics, both of sufficient quality for the whole treatment to be satisfying. C 2015 AIP Publishing LLCA.G.-V. acknowledges support from the Spanish Ministerio de Ciencia e Innovación, Grant No. FIS2011-29596-C02-01, and the COST Action, Grant No. CM1002. The Centro de Supercomputación de Galicia (CESGA) is acknowledged for the use of its resources.Peer Reviewe

Trajectory Reconstruction Techniques for Evaluation of ATC Systems

This paper is focused on trajectory reconstruction techniques for evaluating ATC systems, using real data of recorded opportunity traffic. We analyze different alternatives for this problem, from traditional interpolation approaches based on curve fitting to our proposed schemes based on modeling regular motion patterns with optimal smoothers. The extraction of trajectory features such as motion type (or mode of flight), maneuvers profile, geometric parameters, etc., allows a more accurate computation of the curve and the detailed evaluation of the data processors used in the ATC centre. Different alternatives will be compared with some performance results obtained with simulated and real data sets

A hybrid classical/quantum approach to cluster fragmentation dynamics: Application to the vibrational predissociation of He2Cl2

A new hybrid classical/quantum method is proposed and applied to investigate the vibrational predissociation (VP) dynamics of the He2Cl2 complex. The full dimensionality of the system (assuming zero total angular momentum) is included in the method. The VP process He2Cl2 is dominated by a sequential mechanism of dissociation of the two van der Waals bonds. The hybrid approach describes the first weak bond fragmentation classically, and the second one quantum mechanically. The rotational distribution of the Cl2 fragment is calculated both with the hybrid method and with a fully classical trajectory simulation, and compared with the experimental distribution. The hybrid distribution is found to agree very well with the experimental one, and to involve a substantial improvement with respect to the classical result. © 1998 American Institute of Physics.This work has been supported by the D.G.I.C.Y.T. Grant No. PB95-0071 ~Spain! and the Spanish-French cooperation program PICASSO No. HF1996-0232.Peer Reviewe