Dynamics of Coulomb explosion and kinetic energy release in clusters of heterocyclic compounds

Abstract

The studies presented herein elucidate details of the Coulomb explosion event initiated through the interaction of heterocyclic clusters with an intense femtosecond laser beam (⩾1 PW/cm2). Clusters studied include 7-azaindole and pyridine. Covariance analysis verifies that the fragmentation channels are competitive. Kinetic-energy analyses, from experiment and simulation, suggest that Coulomb exploded fragments are created with varying amounts of energy and have a strong mass-to-charge relationship. Backward-ejected protons are found to impact the repeller and eject adsorbed protons from the surface. Moreover, delayed fragmentation is suggested by fast-Fourier transformation of a proton time-of-flight mass spectrum and confirmed by deconvoluting the aforementioned signal through intensity decrements. Voltage gradient, laser power, and microchannel plate detector studies yield insight into the solvation effect of clusters in the Coulomb explosion event. Conceptually, the dynamic charge resonance enhanced ionization (Dynamic CREI) model best explains these results of heterocyclic Coulomb explosion.

Beyond the Rayleigh instability limit for multicharged finite systems: From fission to Coulomb explosion

“…This can be accomplished either by a marked enhancement of the repulsive Coulomb energy or by the dramatic reduction of the cohesive surface energy. The increase of E(Coulomb) was experimentally attained for cluster Coulomb explosion induced by ultrashort (1-10 fs) multielectron ionization and nuclear dynamics (10-100 fs) of molecular clusters, e.g., ) (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29)(37)(38)(39)(40). Femtosecond electron dynamics, involving inner and outer cluster ionization (29), strips the cluster atoms͞molecules of their outer shell valence electrons, producing highly charged clusters on a time scale shorter than nuclear motion.…”

“…What are the fragmentation channels and under what conditions are they realized? What is the interplay between fission, i.e., instability toward dissociation, of the finite system into two (or a small number of) fragments and Coulomb explosion (17)(18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29) into a large number ϳn (where n is the number of constituents) of ionic species? On the basis of molecular dynamics simulations of the fragmentation patterns of heavily charged Morse clusters we established that the Rayleigh instability limit (30) separates between nearly binary (or tertiary) spatially unisotropic fission and spatially isotropic Coulomb explosion into a large number of ionic fragments.…”

“…Beyond the fissibility limit (X Ͼ 1), barrierless fission and other dissociative channels can open up, but this barrierless domain was not yet explored. In this context, Coulomb explosion of highly charged clusters and large molecules induced by multielectron ionization in ultraintense, ultrashort laser fields (18)(19)(20)(21)(22)(23)(24)(25)(26)(27)(28)(29), as well as the expansion of ultracold optical molasses (34), constitute new dissociative phenomena induced by Coulomb instability of multicharged finite systems or their analogy for finite ultracold gases (34), which…”

Gas-phase dissociation pathways of multiply charged peptide clusters

“…The competing processes of evaporation and fission have been described by various liquid-drop models for clusters as diverse as atomic nuclei [42], multiply charged metal clusters [5,6], and highly charged solvent droplets [2,3]. The recent development of femtosecond lasers capable of rapidly ionizing many molecules in atomic or molecular clusters has permitted access to another dissociation process whereby a cluster undergoes a coulombic explosion, resulting in the isotropic ejection of many charged fragments [12][13][14][15].General characteristics of cluster dissociation are well illustrated by multiply charged metal clusters. Evidence for their dissociation was first observed by Sattler et al who, by measuring the mass and charge of Pb, Xe, and NaI clusters, observed half-integer cluster numbers that were interpreted to be doubly charged clusters [4].…”

“…One motivation behind cluster research is that the transitional characteristics between bulk and molecular properties can be discovered by studying intermediate states of matter. Investigators have explored a wide variety of materials, including charged droplets of various liquids [2,3], clusters of noble metals [4][5][6][7][8], metal-ligand clusters [1,[9][10][11], highly charged clusters of noble gasses [12,13], small molecules [14,15], and ultracold clusters of transition metals [16]. Recently, investigators have formed noncovalently bound clusters of biologically important molecules, including clusters of amino acids and small peptides [17][18][19][20][21][22][23][24][25][26][27][28], and have studied their dissociation processes [18,20,[26][27][28].…”