High-spin multiplicity

ON THE ROLE OF ELECTRONIC MOLECULAR STATES OF HIGH SPIN MULTIPLICITY... 

Abstract Several examples are presented in order to illustrate the crucial role of high spin multiplicity electronic states on the formation and decomposition of the corresponding molecular systems. For instance, these states are good candidates where electronically excited, metastable negative ions can be found. Moreover, they are needed in order to explain fully unimolecular and bimolecular reaction pathways. During these reactions, the importance of the couplings between these states, such as vibronic and Renner-Teller, and with the states of lower spin multiplicity, such as spin-orbit, are pointed out. 

S. Ben Yaghlane, A. Ben Houria, and M. Hochlaf, On The Role of Electronic Molecular States of High Spin Multiplicity, this volume, 2006. 

In this section, we purpose to introduce the concept of regularity and irregularity in the spin state structure. This concept already led to the synthesis of polymetallic systems in which the ground state has a very high spin multiplicity. It might be a key for the design of molecular ferromagnets, as we shall see it in Sect. 12. 

The SAC-CI analytical energy gradient was extended to the general-f method [33,40] and the high-spin multiplicities [37,42]. Formulations and implementations were recently... 

Figure 5 Frontier orbitals of [Cr(fj-CI)(/x-OH)]4. Orbital energies (eV) are determined at DFT level of theory for the high-spin multiplicity = 17 state.

It is of interest to describe spin systems that are completely different from nitrox-ide-labeled dendrimers, but that also bear in their organic structure a high-spin multiplicity (with S > V) High-spin polycarbenes with ji-conjugation, which are the first and second generations of the spin-mediated dendrimers based on pheny-lacetylenes, were studied by a two-dimensional electron-spin transient nutation (2D-ESTN) method based on pulsed-ESR to determine the spin mulliphcity. The contour plots of the 2D-ESTN spectra of the dendrimer at 3.5 K allowed to identify the nutation frequencies, which were attributed to 4, 4> 4, 3>, 4, 3> <-> 4, 2>, 4, 2> 4, 1>, and 4, 1> 4, 0>. The ESR allowed the detec-... 

Consider a free atom or molecule in which several electrons occupy but do not fill a set of orbitals, which need not all be degenerate. There will usually be many ways in which the electrons can be distributed, some of which will be of lower energy than others. The differences in energy will be determined by electron repulsion and the more stable arrangements will be those with the least electron repulsion destabilization. So, electron-electron repulsion will be relatively small if the electrons occupy orbitals which are spatially well separated it will be reduced yet more if the electrons have a high spin multiplicity, i.e. have parallel spins, because two electrons with parallel spins can never be in the same orbital. 

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