Electron and nuclear dynamics of molecular clusters in ultraintense laser fields. IV. Coulomb explosion of molecular heteroclusters

Abstract

In this paper we present a theoretical and computational study of the temporal dynamics and energetics of Coulomb explosion of (CD4)(n) and (CH4)(n) (n=55-4213) molecular heteroclusters in ultraintense (I=10(16)-10(19) W cm(-2)) laser fields, addressing the manifestation of electron dynamics, together with nuclear energetic and kinematic effects on the heterocluster Coulomb instability. The manifestations of the coupling between electron and nuclear dynamics were explored by molecular dynamics simulations for these heteroclusters coupled to Gaussian laser fields (pulse width tau=25 fs), elucidating outer ionization dynamics, nanoplasma screening effects (being significant for I< or =10(17) W cm(-2)), and the attainment of cluster vertical ionization (CVI) (at I=10(17) W cm(-2) for cluster radius R(0)< or =31 A). Nuclear kinematic effects on heterocluster Coulomb explosion are governed by the kinematic parameter eta=q(C)m(A)/q(A)m(C) for (CA(4))(n) clusters (A=H,D), where q(j) and m(j) (j=A,C) are the ionic charges and masses. Nonuniform heterocluster Coulomb explosion (eta >1) manifests an overrun effect of the light ions relative to the heavy ions, exhibiting the expansion of two spatially separated subclusters, with the light ions forming the outer subcluster at the outer edge of the spatial distribution. Important features of the energetics of heterocluster Coulomb explosion originate from energetic triggering effects of the driving of the light ions by the heavy ions (C(4+) for I=10(17)-10(18) W cm(-2) and C(6+) for I=10(19) W cm(-2)), as well as for kinematic effects. Based on the CVI assumption, scaling laws for the cluster size (radius R(0)) dependence of the energetics of uniform Coulomb explosion of heteroclusters (eta=1) were derived, with the size dependence of the average (E(j,av)) and maximal (E(j,M)) ion energies being E(j,av)=aR(0) (2) and E(j,M)=(5a/3)R(0) (2), as well as for the ion energy distributions P(E(j)) proportional to E(j) (1/2); E(j)< or =E(j,M). These results for uniform Coulomb explosion serve as benchmark reference data for the assessment of the effects of nonuniform explosion, where the CVI scaling law for the energetics still holds, with deviations of the a coefficient, which increase with increasing eta. Kinematic effects (for eta>1) result in an isotope effect, predicting the enhancement (by 9%-11%) of E(H,av) for Coulomb explosion of (C(4+)H(4) (+))(eta) (eta=3) relative to E(D,av) for Coulomb explosion of (C(4+)D(4) (+))(eta) (eta=1.5), with the isotope effect being determined by the ratio of the kinematic parameters for the pair of Coulomb exploding clusters. Kinematic effects for nonuniform explosion also result in a narrow isotope dependent energy distribution (of width DeltaE) of the light ions (with DeltaE/E(H,av) approximately 0.3 and DeltaE/E(D,av) approximately 0.4), with the distribution peaking at the high energy edge, in marked contrast with the uniform explosion case. Features of laser-heterocluster interactions were inferred from the analyses of the intensity depen...

Regular multicharged transient soft matter in Coulomb explosion of heteroclusters

“…These transient spherical shells provide a case of soft matter expanding on the femtosecond time scale. The features of such a Coulomb exploding multicharged monolayer of soft matter are qualitatively distinct from the uniform Coulomb explosion of homonuclear multicharged clusters (10,11), e.g., (A ϩ ) n . Information emerges on transient structures, i.e., the mapping of all nuclear ionic coordinates involved in the dynamic process, unveiling facets of ultrafast structural dynamics that are of considerable interest in chemistry, physics, and biology (12,13).…”

“…These analytical results were supplemented by molecular dynamics simulations performed under cluster vertical ionization (CVI) initial conditions (8)(9)(10)(11)15) and by complete molecular dynamics simulations for energetic electrons and ions (8,9) in these heteroclusters, which are subjected to a Gaussian laser field with a peak intensity of I ϭ 10 17 to 10 20 W⅐cm Ϫ2 and a pulse duration of ϭ 25 fs.…”

“…AB Ͼ 1 results in the run-over process (11,15,16) of the light A qAϩ ions relative to the heavy B qBϩ ions. The expansion dynamics manifests a marked contraction of the spatial distribution of the light ions, resulting in a nearly monoionic expanding spherical shell.…”

“…For (AI) n (A ϭ H, D, or T) heteroclusters extremely charged (A ϩ I 25ϩ ) n clusters are generated at I ϭ 10 19 W⅐cm Ϫ2 (Fig. 1), with HI ϭ 5.1 for (H ϩ I 25ϩ ) n , DI ϭ 2.5 for (D ϩ I 25ϩ ) n and TI ϭ 1.7 for (T ϩ I 25ϩ ) n .AB Ͼ 1 results in the run-over process (11,15,16) of the light A qAϩ ions relative to the heavy B qBϩ ions. The expansion dynamics manifests a marked contraction of the spatial distribution of the light ions, resulting in a nearly monoionic expanding spherical shell.…”

“…Information emerges on transient structures, i.e., the mapping of all nuclear ionic coordinates involved in the dynamic process, unveiling facets of ultrafast structural dynamics that are of considerable interest in chemistry, physics, and biology (12, 13). Regarding energetics, interesting applications of Coulomb explosion of an assembly of deuterium containing heteroclusters involve dd nuclear fusion driven by Coulomb explosion (14-16) of heteroclusters (11,(15)(16)(17). For exploding light-heavy atom heteroclusters, e.g., (DI) n , in ultraintense laser fields, the extremely charged I qϩ (q ϭ 7-35) ions act as most effective energetic triggers for driving the expanding D ϩ ions, resulting in a dramatic enhancement of the nuclear fusion driven by Coulomb explosion yields.…”