Vibronic Coupling in Spherically Encapsulated, Diatomic Molecules: Prediction of a Renner–Teller-like Effect for Endofullerenes

Abstract

In the year 1933, Herzberg and Teller realized that the potential energy surface of a triatomic, linear molecule splits into two as soon as the molecule is bent. The phenomenon, later dubbed the Renner–Teller effect due to the detailed follow-up work of Renner on the subject, describes the coupling of a symmetry-reducing molecular vibration with degenerate electronic states. In this article, we show that a very similar type of nonadiabatic coupling can occur for certain translational degrees of freedom of diatomic, electronically degenerate molecules when trapped in a nearly spherical or cylindrical quantum confinement, e.g., realized through electromagnetic fields or molecular encapsulation. We illustrate this on the example of fullerene-encapsulated nitric oxide, and provide a prediction of its interesting, perturbed vibronic spectrum.

Probing the Interaction of NO with C60: Comparison between Endohedral and Exohedral Complexes

“…A significant decrease in the hyperfine coupling constant of boron was reported in the cage compared to its free state. In a recent study, taking NO encapsulated fullerene NO@C 60 as the model system, Hauser and Pototschnig theoretically predicted Renner–Teller-like vibronic coupling in the electronically degenerate heteronuclear diatomic molecule under spherical confinement …”

“…Despite significant progress in the theoretical understanding of various nonmetal paramagnetic species based on fullerene, a systematic theoretical exposition of host–guest interaction between NO and fullerene C 60 has not been carried out. We also note that although several studies are reported about the adsorption of NO over different carbonaceous materials, − the adsorption of NO on fullerene-based materials is rarely addressed in the literature. ,− The present study focuses on the systematic theoretical investigations of the electronic structure, stability, and noncovalent interaction present in NO@C 60 and NO.C 60 complexes with the aid of the quantum theory of atoms in molecules (QTAIM), , noncovalent interactions (NCI), and molecular electrostatic potential (MESP) analyses . Furthermore, a detailed theoretical analysis of the interactions of two NO radicals with C 60 , their energetics, and structural properties at various locations of NO are discussed.…”

“…In a recent study, taking NO encapsulated fullerene NO@C 60 as the model system, Hauser and Pototschnig theoretically predicted Renner−Teller-like vibronic coupling in the electronically degenerate heteronuclear diatomic molecule under spherical confinement. 35 Despite significant progress in the theoretical understanding of various nonmetal paramagnetic species based on fullerene, a systematic theoretical exposition of host−guest interaction between NO and fullerene C 60 has not been carried out. We also note that although several studies are reported about the adsorption of NO over different carbonaceous materials, 36−42 the adsorption of NO on fullerene-based materials is rarely addressed in the literature.…”

Neglected Importance of Anharmonicity in Quantifying the Renner–Teller Effect

“…This definition of ε has been widely used in characterizing the RT effect, even till today. ,− For an extension, very recently, it was shown that the NO molecule encapsulated in a fullerene can also experience a vibronic coupling effect very similar to the RT effect regarding the NO translation . Thus, the RT parameter may not only characterize the distortion of linear molecules but also quantify energy splitting of more complex systems.…”

Quantum Criticality and Universal Behavior in Molecular Dipolar Lattices of Endofullerenes

“…Interesting electronic effects such as vibronic couplings will be explored in future work. 40 The results presented here show a rather small energy splitting of 1−2 K between the first two oppositely polarized states, which might suggest a comparably low Curie temperature of a few Kelvin. However, this temperature strongly depends on the density of states and the polarization of the excited states.…”