arXiv subjects

Michael Roemelt

Publications and source records attributed to Michael Roemelt.

3 recordsLinked to original sources

arXiv2026

Spin-cavity interactions in relativistic Jahn-Teller systems under strong light-matter coupling

We extend our recent work on the cavity-modified spin Zeeman effect of an effective spin-1/2-system[J. Chem. Phys. 163, 174307 (2025)] to a relativistic Jahn-Teller scenario under strong light-matter coupling. Here, the effective spin-1/2-system is realized via a single electron or a single hole in a doubly-degenerate molecular orbital system of trigonal symmetric transition metal complexes. Both single-particle and single-hole systems are subject to both vibronic and spin-orbit coupling (SOC) augmented by interactions with a quantized cavity field via the cavity Zeeman interaction. Methodologically, we combine the relativistic $E\times e$-Jahn-Teller model with a recently introduced effective Hamiltonian formalism based on quasi-degenerate perturbation theory, which treats the cavity-spin interaction in leading order beyond the dipole approximation. We derive analytic expressions for Kramers pair energies in weak and strong SOC regimes as well as related cavity-modified effective electronic g-factors. We find cavity-induced modifications of the electronic g-factor to become relevant in the weak SOC regime for both single-particle and single-hole systems while being effectively quenched under strong SOC. Alternating signs of the cavity-Zeeman correction render single-particle and single-hole scenarios distinct in their response to the cavity field from a g-factor perspective.

physics.chem-ph↗

arXiv2026

Nucleophilic substitution at silicon under vibrational strong coupling: Refined insights from a high-level ab initio perspective

We study the bimolecular nucleophilic substitution (S$_\mathrm{N}$2) reaction of 1-phenyl-2-trimethylsilylacetylene (PTA) under vibrational strong coupling (VSC) from the perspective of high-level ab initio quantum and polaritonic chemistry. Specifically, we address conflicting mechanistic proposals, cavity-induced electronic corrections under VSC and the relevance of a previously debated Si-C-stretching motion of PTA for vibrational polariton formation. We first provide computational evidence for a two-step mechanism based on density functional theory and high-level coupled cluster results, identify new encounter and products complexes and illustrate the relevance of diffuse basis functions for a qualitatively correct description of anionic reactive systems. We subsequently show that cavity-induced dipole fluctuation corrections of electronic energies can be significant on the level of cavity Born-Oppenheimer coupled cluster theory and discuss their qualitative impact on the proposed two-step mechanism taking into account cavity-induced molecular reorientation. We finally show that the Si-C-stretching contribution to the experimentally relevant double-peak feature of PTA exhibits a dominant dipole character, which renders it central for linear IR response and vibrational polariton formation despite the presence of CH$_3$-rocking contributions. The dipole character along the cleaving Si-C-bond is eventually shown to rationalize Rabi splittings throughout the proposed two-step mechanism. Our work refines the microscopic perspective on the S$_\mathrm{N}$2 reaction of PTA under VSC and highlights recent developments in ab initio polaritonic chemistry for the VSC regime.

physics.chem-ph↗

arXiv2025

Cavity-Modified Zeeman Effect via Spin-Polariton Formation

We study the electronic spin Zeeman effect for an effective spin-$1/2$-system subject to both strong coupling to a low-frequency optical cavity and an external static magnetic field. Specifically, we address the interplay between the cavity magnetic field component in a cavity Zeeman interaction and the canonical spin Zeeman interaction from the perspective of an effective spin-polariton Hamiltonian. The latter is derived from the minimal coupling Pauli-Fierz Hamiltonian beyond the common dipole approximation via first-order quasi-degenerate perturbation theory. We find the spin Zeeman effect to be modified in the presence of the cavity field due to the formation of spin-polariton states, which result from an intricate interplay of cavity and external magnetic fields in our model. Spin-polariton signatures are discussed in the context of electron paramagnetic resonance (EPR) spectroscopy along with cavity-induced modifications of the electronic g-factor.

physics.chem-ph↗