Abstract
Nuclear magneto-optic (NMO) effects are recently described phenomena originating from the interaction of light with local magnetic fields produced by nuclear spins. The phenomena border nuclear magnetic resonance and optical spectroscopy and are expected to provide rather unique spectroscopic features, borrowing from both localized response of the atomic nuclei as well as more global excitation properties of the whole molecule or its chromophore moieties. A number of quantum-chemical computational studies have been carried out, offering a reasonable agreement with nuclear magneto-optics experiments performed so far. However, the detailed structure-spectra relation is still poorly understood. In this report we address the question of locality of one of the NMO effects, namely nuclear spin-induced circular dichroism (NSCD). We implement an alternative computational approach for calculation of the NSCD intensities, based on residues of quadratic response functions, and use it to investigate the NSCD response of different nuclei in a model molecular system with well-defined separate chromophores. The results show that significant NSCD at a given energy only occurs at the nuclei which are located in the chromophore that is excited. We rationalize these findings using analysis via difference densities, and approximate sum-over-states calculations. This behaviour of NSCD opens a way to experimental studies of localization of excited states in molecules, potentially with resolution down to the order of bond-length.
Highlights
Nuclear magneto-optic spectroscopy (NMOS) is an umbrella term for a group of spectroscopic effects that have been experimentally and theoretically investigated in recent years
The purpose of this study is twofold: First, we present an alternative method to complex polarization propagator (CPP) for calculating nuclear spin-induced circular dichroism (NSCD), based on residues of quadratic response functions,[24,25,26] to tackle the issue of obtaining analytical NSCD intensities for individual excited states
As anticipated in the Methods section, the new implementation was tested for consistency via comparison of NSCD computed via eqn (7) and (8) with that obtained using the CPP protocol
Summary
Nuclear magneto-optic spectroscopy (NMOS) is an umbrella term for a group of spectroscopic effects that have been experimentally and theoretically investigated in recent years. NMOS effects manifest themselves as changes in polarization state of the light upon interaction with a sample possessing a macroscopic nuclear magnetization. In addition to NSOR, several other NMOS effects have been theoretically predicted. These include three Cotton–Mouton-like effects: nuclear spin-induced Cotton–Mouton effect (NSCM),[11,12] nuclear spin-induced Cotton–Mouton effect in external magnetic field (NSCM-B),[13,14] and nuclear quadrupole-induced Cotton– Mouton effect (NQCM).[15,16] Most recently, nuclear spin-induced circular dichroism (NSCD) has been theoretically investigated.[17,18,19,20]
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