Jahn–Teller Effects in Molecules on Surfaces with Specific Application to C60

Abstract

A note on versions:The version presented here may differ from the published version or from the version of record. If you wish to cite this item you are advised to consult the publisher's version. Please see the repository url above for details on accessing the published version and note that access may require a subscription. Abstract Scanning tunnelling microscopy (STM) is capable of imaging molecules adsorbed onto surfaces with sufficient resolution as to permit intramolecular features to be discerned. Therefore, imaging molecules subject to the Jahn-Teller (JT) effect could, in principle, yield valuable information about the vibronic coupling responsible for the JT effect. However, such an application is not without its complications. For example, the JT effect causes subtle, dynamic distortions of the molecule; but how will this dynamic picture be affected by the host surface? And what will actually be imaged by the rather slow STM technique? Our aim here is to present a systematic investigation of the complications inherent in JT-related STM studies, to seek out possible JT signatures in such images and to guide further imaging towards identification and quantification of JT effects in molecules on surfaces. In particular, we consider the case of surface-adsorbed C 60 ions because of their propensity to exhibit JT effects, their STM-friendly size and because a better understanding of the vibronic effects within these ions may be important for realisation of their potential application as superconductors.

Calculation of images of orientedC60molecules using molecular orbital theory

“…However, some preliminary results, concerned with the dynamical aspect of the problem as applied to E e and T h coupling regimes, including a discussion relating to charge transfer, may be found in Ref. 36.…”

The effect of cooperative Jahn–Teller interactions on C60−anions

“…In general, the interaction of a C 60 anion with a surface will also lead to a distortion of a system. It has therefore been suggested that surface interactions could be written (again phenomenologically), at least to a first approximation, in terms of an expansion in the σ λ for an h mode, which would result in a similar symmetry-lowering distortion to that used to describe co-operative JT effects [30]. However, to do this, the relevant operators must have a symmetry appropriate to that of both the adsorbed molecule and of the surface.…”

Manifestation of dynamic Jahn–Teller distortions and surface interactions in scanning tunnelling microscopy images of the fullerene anion C−60

“…Our treatment has ignored the effect of these displacements on STM images, as these are expected to be negligibly small. Significant displacement of the nuclei during pseudorotation would 'blur' the images presented here, as in the case of an E ⊗ e system [2].…”

“…The results are also shown in table 1. As the timescale of an STM experiment is expected to be orders of magnitude larger than the time taken to tunnel between equivalent configurations [2], all equivalent (isoenergetic) distortions in a set will be imaged together in an STM experiment. In the table, groups on the same line separated by braces are related to each other by reflections in the x-z plane.…”

“…However, there will be a set of isoenergetic distortions, referred to as 'orientomers' in [1], which look identical to each other but have different relative orientations. For realistic coupling strengths, tunnelling between these orientomers is expected to take place on a timescale that is fast compared to the millisecond timescale of the STM technique, even at low temperatures [2]. This dynamic JT effect must be taken into account when simulating observed STM images.…”