Microscopic theory of Raman scattering for the rotational organic cation in metal halide perovskites

TL;DR

This paper develops a microscopic theory of Raman scattering for the rotational organic cation in metal halide perovskites, revealing how phonon angular momentum and molecular orientation can be deduced from Raman spectra.

Contribution

It introduces a novel microscopic framework for understanding Raman scattering involving rotational organic cations in perovskites, including selection rules and angular momentum transfer.

Findings

Phonon angular momentum manifests as Raman shifts.

Initial orientation and rotational directions of ROC can be inferred from spectra.

The theory provides a foundation for high-precision molecular rotation analysis.

Abstract

A gap exists in microscopic understanding the dynamic properties of the rotational organic cation (ROC) in the inorganic framework of the metal halide perovskites (MHP) to date. Herein, we develop a microscopic theory of Raman scattering for the ROC in MHP based on the angular momentum of a ROC exchanging with that of the photon and phonon. We systematically present the selection rules for the angular momentum transfer among three lowest rotational levels. We find that the phonon angular momentum that arising from the inorganic framework and its specific values could be directly manifested by Stokes (or anti-Stokes) shift. Moreover, the initial orientation of the ROC and its preferentially rotational directions could be judged in Raman spectra. This study lays the theoretical foundation for the high-precision resolution and manipulation of molecular rotation immersed in many-body environment by Raman technique.