Ultrafast dissociation of a core-ionized water molecule in liquid phase: density functional theory based simulations. C R Stia∗, 1 , M -P Gaigeot† , M -A Herv´ e du Penhoat§ , R Vuilleumier‡ , O A Foj´ on∗ , I k § Tavernelli , and M -F Politis ∗
†
IFIR, CONICET-Universidad Nacional Rosario, Av. Pellegrini 250, 2000 Rosario, Argentina. LAMBE, UMR-CNRS 8587, Universit´e d’Evry, Blvd F. Mitterrand, Bˆat. Maupertuis, 91025 Evry, France § IMPMC, Universit´e Pierre et Marie Curie, Campus Boucicaut, 140 rue de Lourmel, 75015 Paris, France ‡ LPTMC, UMR-CNRS 7600, Universit´e Pierre et Marie Curie, 4 place Jussieu, 75005 Paris, France. k EPFL, Institut des Sciences et Ing´enierie Chimiques, 1015 Lausanne, Switzerland. Synopsis We investigate the dynamics of a core-ionized molecule in liquid water by performing first-principles density functional theory (DFT)-based simulations. We observe that molecular dissociation is reached within the lifetime of the induced vacancy. Our findings show that at least one of the intramolecular hydrogens migrates from the core- ionized molecule to one molecule of the first solvation shell.
Core-hole states have a strongly dissociative character. In particular, they may induce ultrafast dissociation reactions in which the nuclear dynamics takes place on the same time scale of the lifetime of the core vacancies. In this work we study the fragmentation dynamics of a single core-ionized water molecule in liquid water within the framework of ab initio DFT-based MD simulations [1]. We investigate the molecular fragmentation subsequent to core-hole creation by explicitly averaging over several initial conditions (atomic positions and velocities). The computations are performed by using the norm-conserving Troullier-Martins pseudopotentials [2] and the BLYP functional [3] for a periodic box consisting of 32 water molecules in liquid phase [4]. Core-ionization of one of the 32 water molecules is generated with the following procedure. The norm-conserving pseudopotential of one of the oxygen atoms is replaced by a developed pseudopotential for the full-core-hole state, describing a 1s1 2s2 2p4 electron configuration [5]. In this way, the initial ionized-state evolution is simulated on a femtosecond time scale. Our results predict that the dissociation of the core-ionized molecule may be reached during the lifetime of inner-shell hole (about 5fs). Indeed, our calculations lead to neutral OH as primary outcomes. We observe also a second fragmentation channel in which total Coulomb explosion of the ionized molecule occurs. These results are compared with those obtained in the framework of the X-ray spectroscopy [6]. Preliminary time-dependent DFT simulations [7] are 1
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also presented in this work. (a)
t=0
t = 5 fs
t = 10 fs
t=0
t = 5 fs
t = 10 fs
(b)
Fig. 1. Centers of the localized Wannier functions [8] computed on the fly along especially chosen trajectories leading to either (a) OH/H3 O+ pairs or (b) Coulomb explosion.
References [1] Car R and Parrinello M 1985 Phys. Rev. Lett 55 2471. [2] Troullier N and Martins J L 1991 Phys. Rev. B 43 1993. [3] Becke A 1988 Phys. Rev. A 38 3098; Lee C et al. 1988 Phys. Rev. B 37 785. [4] Hunt P, et al. 2003 Chem. Phys. Lett 376 68. [5] Brena B, et al. 2004 Phys. Rev. Lett 93 148302. [6] Odelius M, et al. 2005 Phys. Rev. Lett 94 227401. [7] Tavernelli I, et al. 2006 Phys. Rev. B 73 094204. [8] Marzari N and Vanderbilt D 1997 Phys. Rev. B 56 12847.
