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Title: Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate

Abstract

Unimolecular and collision-induced dissociation of doubly charged lithium acetate clusters, (CH3COOLi)nLi22+, demonstrated that Coulomb fission via charge separation is the dominant dissociation process with no contribution from the neutral evaporation processes for all such ions from the critical limit to larger cluster ions, although latter process have normally been observed in all earlier studies. These results are clearly in disagreement with the Rayleigh’s liquid drop model that has been used successfully to predict the critical size and explain the fragmentation behavior of multiply charged clusters.

Authors:
 [1]
  1. Pacific Northwest National Laboratory, Richland WA 99354 USA
Publication Date:
Research Org.:
Pacific Northwest National Lab. (PNNL), Richland, WA (United States)
Sponsoring Org.:
USDOE
OSTI Identifier:
1342321
Report Number(s):
PNNL-SA-114548
Journal ID: ISSN 0951-4198; KP1704020
DOE Contract Number:
AC05-76RL01830
Resource Type:
Journal Article
Resource Relation:
Journal Name: Rapid Communications in Mass Spectrometry; Journal Volume: 30; Journal Issue: 13
Country of Publication:
United States
Language:
English
Subject:
Cluster Ions; Coulomb Fission; Liquid Drop Model

Citation Formats

Shukla, Anil. Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate. United States: N. p., 2016. Web. doi:10.1002/rcm.7597.
Shukla, Anil. Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate. United States. doi:10.1002/rcm.7597.
Shukla, Anil. Wed . "Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate". United States. doi:10.1002/rcm.7597.
@article{osti_1342321,
title = {Dissociation of doubly charged clusters of lithium acetate: Asymmetric fission and breakdown of the liquid drop model: Dissociation of doubly charged clusters of lithium acetate},
author = {Shukla, Anil},
abstractNote = {Unimolecular and collision-induced dissociation of doubly charged lithium acetate clusters, (CH3COOLi)nLi22+, demonstrated that Coulomb fission via charge separation is the dominant dissociation process with no contribution from the neutral evaporation processes for all such ions from the critical limit to larger cluster ions, although latter process have normally been observed in all earlier studies. These results are clearly in disagreement with the Rayleigh’s liquid drop model that has been used successfully to predict the critical size and explain the fragmentation behavior of multiply charged clusters.},
doi = {10.1002/rcm.7597},
journal = {Rapid Communications in Mass Spectrometry},
number = 13,
volume = 30,
place = {United States},
year = {Wed Jun 08 00:00:00 EDT 2016},
month = {Wed Jun 08 00:00:00 EDT 2016}
}
  • We have used the finite-range, rotating-liquid-drop model to calculate the conditional saddle-point shapes, fission barriers, and moments of inertia of the nucleus {sup 149}Tb as functions of mass asymmetry (or fragment charge {ital Z}) and angular momentum. A strong motivation in the present work is the potentiality for predicting total kinetic energies (TKE) in asymmetric fission, which may be compared with measurements of intermediate-mass fragments (IMF's) produced in heavy-ion reactions. From the conditional saddle points, we estimate the TKE in the limit of no post-saddle dissipation, yielding, in effect, upper limits for the TKE's. Clearly the nuclear shapes at scissionmore » will produce lower limits for the TKE's, and we propose two methods for determining the characteristics of such scission configurations. The first involves a linear extrapolation along the fission normal mode at the conditional saddle point, and the second employs Swiatecki's scaling rule to determine the effect of dissipation on the nuclear elongation at scission. In comparison to experimental TKE results for IMF's, corrected for light particle evaporation, we find that the predictions from saddle-point shapes are in rather good agreement with the data over a wide range of mass asymmetry. The calculated estimates from nondissipative scission-point configurations also agree fairly well with the data, but tend to underpredict the TKE's significantly for the heavier IMF's. This is not a serious concern, as the calculations have not included any prescission damping. The estimates from fully dissipative scission-point shapes are systematically low, falling appreciably below the data over the whole range studied.« less
  • The average ground-state energy of a charged spherical metal cluster with {ital N} atoms and {ital z} excessive valence electrons, i.e., with net charge {ital Q}={minus}{ital ez} and radius {ital R}={ital r}{sub {ital sN}}{sup 1/3}, is presented in the liquid drop model (LDM) expansion {ital E}({ital N},{ital z})={ital a}{sub v}{ital N}+{ital a}{sub s}{ital N}{sup 2/3}+{ital a}{sub c}{ital N}{sup 1/3}+{ital a}{sub 0}({ital z})+{ital a}{sub {minus}1}({ital z}){ital N}{sup {minus}1/3}+{ital O}({ital N}{sup {minus}2/3}). We derive analytical expressions for the leading LDM coefficients {ital a}{sub v}, {ital a}{sub s}, {ital a}{sub c}, and, in particular, for the charge dependence of the further LDM coefficientsmore » {ital a}{sub 0} and {ital a}{sub {minus}1}, using the jellium model and density functional theory in the local density approximation. We obtain for the ionization energy {ital I}({ital R})={ital W}+{alpha}({ital e}{sup 2}/{ital R})+{ital O}({ital R}{sup {minus}2}), with the bulk work function {ital W}=[{Phi}(+{infinity}){minus}{Phi}(0)]{minus}{ital e}{sub b}, given first by Mahan and Schaich in terms of the electrostatic potential {Phi} and the bulk energy per electron {ital e}{sub b}, and a new analytical expression for the dimensionless coefficient {alpha}. We demonstrate that within classical theory {alpha}=1/2 but, in agreement with experimental information, {alpha} tends to {approximately}0.4 if quantum-mechanical contributions are included. In order to test and confirm our analytical expressions, we discuss the numerical results of semiclassical density variational calculations in the extended Thomas{endash}Fermi model. Copyright {copyright} 1996 Academic Press, Inc.« less