# Bridging Vibrations and Spins: Mode-Resolved Spin–Phonon Coupling Revealed through THz EPR/Magnetic IR Simulation

## TL;DR

This paper introduces a new simulation method to study how electron spins interact with vibrations in molecules, using THz EPR/Magnetic IR spectroscopy for quantum information applications.

## Contribution

The first comprehensive simulation protocol to extract spin–phonon coupling parameters from THz EPR/Magnetic IR spectra.

## Key findings

- The method was validated using a tetrahedral high-spin Co(II) complex.
- The dominant coupling is attributed to a twisting mode of the first coordination sphere.
- Good agreement was found between experiment, simulation, and quantum-chemical calculations.

## Abstract

Molecular electron spin qubits show great potential for
quantum
information storage and processing but require paramagnetic systems
with slow relaxation, where coherence is limited by spin–phonon
coupling. Understanding this coupling remains challenging due to scarce
observables and conflicting models, making direct experimental insights
crucial. Vibrational spectroscopy (IR and Raman) under magnetic fields
provides a promising approach. Here, we present the first comprehensive
simulation protocol to extract spin–phonon coupling parameters
from THz EPR/Magnetic IR spectra. Different spectral features are
illustrated using a one-phonon model, emphasizing cases where the
coupling is weaker than the line width. Using a tetrahedral high-spin
Co­(II) complex, we validate the method and benchmark it against quantum-chemical
calculations. The dominant coupling is attributed to a twisting mode
of the first coordination sphere. Excellent agreement among experiment,
simulation, and computation demonstrates the power of THz EPR/Magnetic
IR spectroscopy as a direct probe of spin–phonon coupling.