Observation of Resonant Tunneling from Molecular Shape into Vibronic Feshbach Resonances Followed by Mode-Specific Fragmentation

TL;DR

This study investigates how electrons resonantly attach to and cause dissociation in OCS molecules, revealing mode-specific vibronic Feshbach resonances and non-adiabatic tunneling effects through combined experimental and advanced theoretical methods.

Contribution

It provides the first detailed analysis of mode-specific vibronic Feshbach resonances and non-adiabatic tunneling in electron-induced dissociation of OCS, supported by high-level quantum calculations.

Findings

Resonant electron attachment leads to mode-specific vibronic Feshbach resonances.

Non-adiabatic resonant tunneling governs avoided crossings during dissociation.

Experimental data aligns well with advanced theoretical predictions.

Abstract

We present a kinematically complete study of dissociative electron attachment (DEA) in linear OCS molecules, focusing on how electrons resonantly attach and trigger dissociation. Near the Franck-Condon regime, DEA is dominated by molecular shape resonances, where transient OCS$^-$ states form with high vibrational amplitudes, spectroscopically evident as broad features in DEA cross-sections. As the electron beam energy increases from 5.5 to 6.0 eV, S$^-$ population shifts from lower to higher-energy highly dense bending vibrational states, reinforcing our findings on dipole-forbidden vibronic intensity borrowing. Our advanced potential energy curve calculations, employing the Equation-of-motion coupled cluster singles and doubles for electron attachment (EA-EOMCCSD) method, reveal that beyond the shape resonance, non-adiabatic resonant tunneling governs the avoided crossings, dynamically generating three mode-specific vibronic Feshbach resonances before complete dissociation into three distinct kinetic energy bands of S$^-$. Our theoretical results probe most of the experimental observations quantitatively and qualitatively. These insights deepen our fundamental understanding of resonance-mediated dissociation in electron-molecule resonant scattering, with broader implications for quantum mechanics, plasma physics, vibrational revival, astrochemistry, and radiation damage research.