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Title: A test of the significance of intermolecular vibrational coupling in isotopic fractionation

Intermolecular coupling of dipole moments is studied for a model system consisting of two diatomic molecules (AB monomers) arranged co-linearly and which can form non-covalently bound dimers. The dipolar coupling is a function of the bond length in each molecule as well as of the distance between the centers-of-mass of the two molecules. The calculations show that intermolecular coupling of the vibrations results in an isotope-dependent modification of the AB-AB intermolecular potential. This in turn alters the energies of the low-lying bound states of the dimers, producing isotope-dependent changes in the AB-AB dimer partition function. Explicit inclusion of intermolecular vibrational coupling then changes the predicted gas-dimer isotopic fractionation. In addition, a mass dependence in the intermolecular potential can also result in changes in the number of bound dimer states in an equilibrium mixture. This in turn leads to a significant dimer population shift in the model monomer-dimer equilibrium system considered here. Finally, the results suggest that intermolecular coupling terms should be considered when probing the origins of isotopic fractionation.
Authors:
 [1] ; ORCiD logo [2] ; ORCiD logo [2] ; ORCiD logo [2]
  1. Tulane Univ., New Orleans, LA (United States)
  2. Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Publication Date:
Report Number(s):
LA-UR-16-23718
Journal ID: ISSN 0301-0104
Grant/Contract Number:
AC52-06NA25396
Type:
Accepted Manuscript
Journal Name:
Chemical Physics
Additional Journal Information:
Journal Volume: 494; Journal ID: ISSN 0301-0104
Publisher:
Elsevier
Research Org:
Los Alamos National Lab. (LANL), Los Alamos, NM (United States)
Sponsoring Org:
USDOE National Nuclear Security Administration (NNSA), Office of Defense Nuclear Nonproliferation (NA-20)
Country of Publication:
United States
Language:
English
Subject:
37 INORGANIC, ORGANIC, PHYSICAL, AND ANALYTICAL CHEMISTRY; isotopic fractionation; intermolecular vibrational coupling
OSTI Identifier:
1372793