Monte Carlo simulation of acetonitrile clusters [CH3CN] N , N=2–256: Melting transitions and even/odd character of small clusters (N=2–9), heat capacities, density profiles, fractal dimension, intracluster dimerization, and dipole orientation

Authors

D. Wright, Virginia Commonwealth University
M. Samy El-Shall, Virginia Commonwealth UniversityFollow

Document Type

Article

Original Publication Date

1994

Journal/Book/Conference Title

The Journal of Chemical Physics

Volume

100

Issue

5

DOI of Original Publication

10.1063/1.466367

Comments

Originally published at http://dx.doi.org/10.1063/1.466367

Date of Submission

October 2015

Abstract

The thermodynamic and structural properties of acetonitrile clusters [CH₃CN] _N , N=2–15, 20, 30, 60, 128, and 256 have been investigated using Monte Carlo simulation. Interactions in the small clusters (N≤9) are dominated by antiparallel pairing of the molecular dipoles. The simulations reveal rigid ↔ fluid (melting) transitions with a remarkable even–odd alternation in the transition temperatures for the N=2–9 clusters. The higher melting temperatures of the even‐N clusters arise as consequences of the antiparallel paired dipoles which provide favorable electrostatic interactions. Even–odd alternation has also been observed in the configurational energies and heat capacities and the percentage of molecules possessing an antiparallel nearest neighbor. These observations are consistent with the fact that Coulomb potential terms dominate the interaction energies in clusters with NN≳60 is fairly well represented by the bulk liquid density. Order parameters characterizing dipole orientation indicate that the molecular dipoles tend to lie flat on the cluster surface for N≥30. Significant dimerization within the clusters suggests evaporation of molecules via dimers and an enhancement of evaporative loss over condensation and this may explain the slower nucleation rates observed for acetonitrile compared to the predictions of the classical nucleation theory.

Rights

Wright D., and El-Shall, M. S. Monte Carlo simulation of acetonitrile clusters [CH3CN] N , N=2–256: Melting transitions and even/odd character of small clusters (N=2–9), heat capacities, density profiles, fractal dimension, intracluster dimerization, and dipole orientation. The Journal of Chemical Physics, 100, 3791 (1994). Copyright © 1994 American Institute of Physics.

Is Part Of

VCU Chemistry Publications