PHYSICAL REVIEW A 89, 023403 (2014) Electron-nuclear dynamics of the one-electron nonlinear polyatomic molecule H 2+ 3 in ultrashort intense laser pulses C. Lefebvre, * H. Z. Lu, S. Chelkowski, and A. D. Bandrauk † Laboratoire de Chimie Th´ eorique, D´ epartement de Chimie, Universit´ e de Sherbrooke, Sherbrooke, Qu´ ebec, J1K 2R1 Canada (Received 27 November 2013; published 6 February 2014) A quantum description of the one-electron triangular H 2+ 3 molecular ion, beyond the Born-Oppenheimer approximation, is used to study the full influence of the nuclear motion on the high-intensity photoionization and harmonic generation processes. A detailed analysis of electron and proton motions and their time-dependent acceleration allows for identification of the main electron recollision events as a function of time-dependent configuration of the protons. High-order-harmonic generation photons are shown to be produced by single- electron recollision in the second half of the pulse envelope, which also induces a redshift in the harmonics, due to the rapid few-femtosecond motions of protons. Perpendicular harmonics are produced, in general, with a linearly polarized laser pulse parallel to a bond of the triangular molecule, and, in particular, the harmonics in the cutoff region are elliptically polarized. When the laser-pulse polarization is parallel to a symmetry axis of the triangular molecular ion, creation and destruction of the chemical bond perpendicular to the polarization is predicted on a near-femtosecond time scale. DOI: 10.1103/PhysRevA.89.023403 PACS number(s): 33.80.Wz, 42.50.Ct, 42.50.Hz, 42.65.Ky I. INTRODUCTION Ultrafast quantum dynamic imaging of molecules is cur- rently developing as a new science with the help of the most recent advances in laser technology [1]. To perform dynamic imaging of molecules, one has to take into account the different time scales in the motion of the particles within a molecule. Nuclei evolve on the time scale of the femtosecond (1fs = 10 −15 s). For instance, by applying a femtosecond laser pulse of a few optical cycles, in the near-infrared spectral region, the ultrafast vibrational wave-packet dynamics in the dissociative ionization of the H 2 molecule has been probed successfully [2]. On the other hand, electrons evolve on the time scale of the attosecond (1 as = 10 −18 s). Only recently have ultrashort laser pulses with such comparable durations been produced from the nonlinear and nonperturbative interaction of matter with light through the process of high-order-harmonic generation (HHG) in atoms [3] and molecules (MHOHG) [4]. In this process, an atom or a molecule is ionized by an intense femtosecond infrared laser pulse. The photoelectron is subsequently accelerated by the laser field. As the electric field changes phase within an optical cycle, the ionized electron changes its direction and recollides with the parent ion [3]. Alternatively, the electron may recollide with the neighboring ions at higher energies than recollision with the parent ion [4]. High-energy photons of the order N are emitted in the form of high-order harmonics of the carrier-wave frequency ω, with a maximum energy N ω = I p + 3.17U p , where I p is the ionization potential and U p is the ponderomotive energy in atoms [3] and beyond for molecules [4]. The high order of generated harmonics is the current source of ultrashort pulses of duration of few as’s, which can be used to image the electron dynamics in atoms and molecules [1,5]. * Present address: INRS-EMT, 1650 Boulevard Lionel-Boulet, Varennes, Qu´ ebec, J3X 1S2, Canada; catherine.lefebvre@emt.inrs.ca † andre.bandrauk@usherbrooke.ca Numerical simulations are playing an important role in the understanding of laser-matter interaction, in particular in quantum molecular dynamic imaging [1]. The exact description of molecular dynamics should include the cor- related electron-nuclear motion. So far, large-scale numerical solutions of the multidimensional time-dependent Schr ¨ odinger equation (TDSE) have been used to simulate the nonlinear nonperturbative interaction of a one-electron linear polyatomic molecule with ultrashort laser pulses on time scales of both nuclear and electron motion. In particular, the linear H 2+ 3 one-electron ion has been studied in a one-dimensional (1D), static nuclei simulation [6], to establish in polyatomics the existence of a nonlinear phenomenon unique to molecules, i.e., charge resonance enhanced ionization (CREI) [7]. Using an exterior complex scaling transformed B-spline basis-set expansion, Bian et al. confirmed this phenomenon in the three-dimensional (3D) linear H 2+ 3 in [8]. The same prob- lem was addressed numerically for the linear two-electron 1D H 3 + system where enhanced ionization was shown to involve charge-transfer (CT) states [9]. The effect of nu- clear motion was shown to substantially reduce electron- rescattering effects from H 2+ 3 to H 3 + in the energy range up to 10U p [10]. In the present work, we examine electron ionization and rescattering of the 2D nonlinear (triangular) one-electron H 2+ 3 . Coulomb explosion imaging of H 2+ 3 has been studied previously to monitor two- and three-body kinematical cor- relations in dissociative recombination of H 3 + [11] due to the importance of this phenomena in low-energy plasmas [12] and in the chemistry of interstellar medium [13]. Laser-induced electron localization in H 2+ 3 in the equilateral configuration has recently been reported with Born-Oppenheimer simulations [14]. The H 3 + ion has been recently shown to be formed by unusual proton-transfer mechanisms in organic molecules exposed to femtosecond intense laser pulses [15,16]. H 3 + and H 2+ 3 , due to their unique equilateral triangular geometry, thus provide a fundamentally original system for the theoretical development of the nonperturbative response of nonlinear molecules to intense laser pulses, as recently pointed out in 1050-2947/2014/89(2)/023403(12) 023403-1 ©2014 American Physical Society