Stark effect in the benzene dimer

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Journal titleJournal of Physical Chemistry A
Pages1377513778; # of pages: 4
SubjectAb initio calculations; Asymmetric top; Dynamics calculations; Equilibrium structures; Fourier transform microwave spectroscopy; Intermolecular potentials; Internal rotations; Torsional motion; Benzene; Dimers; Microwave spectroscopy; Molecules; Stark effect
AbstractAb initio calculations of the six-dimensional intermolecular potential have shown the benzene dimer to be an asymmetric top molecule at equilibrium with one benzene moiety forming the "stem" and the other a "tilted cap" in a T-shaped structure. Internal rotation of the cap about its C 6 axis is essentially free; the barriers for cap tilting and for internal rotation of the stem about its C6 axis are hindered by successively higher barriers. In previous work we have validated these theoretical results using Fourier transform microwave spectroscopy in conjunction with dynamics calculations. We have also measured the Stark effect, and despite the fact that the equilibrium structure is that of an asymmetric top, the assigned transitions involving K = 0 exhibit a second-order Stark effect whereas those involving K = 1 exhibit a first-order Stark effect. This is typical for a symmetric-top molecule, but anomalous for an asymmetric-top molecule. We use symmetry arguments to explain how this asymmetric-top molecule can have a first-order Stark effect in certain states that have excitation of cap internal rotation. Cap internal rotation is essentially the twisting of the monomers relative to each other about the intermolecular axis, and such torsional motion occurs in other asymmetric top dimers such as benzene-CO and benzene-H2O. These latter dimers will also have levels that exhibit a first-order Stark effect, which we can explain using our symmetry arguments. © 2013 American Chemical Society.
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AffiliationNational Research Council Canada (NRC-CNRC)
Peer reviewedYes
NPARC number21270903
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Record identifiere08fc927-7701-49f4-afc8-aa42bf27d28a
Record created2014-02-18
Record modified2016-05-09
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