Resonances and Dissociative Electron Attachment in HNCO

Area of Science:

• Physical Chemistry
• Quantum Chemistry
• Molecular Physics

Background:

• Dissociative electron attachment (DEA) is a fundamental process in molecular physics.
• Understanding DEA in polyatomic molecules like isocyanic acid (HNCO) is crucial for various chemical and physical phenomena.
• Previous studies on HNCO DEA have lacked detailed theoretical and experimental correlation.

Purpose of the Study:

• To experimentally and theoretically investigate the dissociative electron attachment process in isocyanic acid (HNCO).
• To identify and characterize the autoionizing state responsible for the formation of the NCO⁻ fragment.
• To develop a theoretical model for the nuclear dynamics governing this process.

Main Methods:

• Combined experimental and theoretical approach.
• Measurement of absolute cross sections for NCO⁻ fragment production.
• R-matrix calculations and analytic continuation in the coupling constant (ACC) for theoretical analysis.
• Development of a one-dimensional nonlocal model for nuclear dynamics.

Main Results:

• Experimental observation of a sharp onset and fine structures in the NCO⁻ cross section near the threshold.
• Identification of the A' resonance with mixed π*/σ* character as the responsible autoionizing state.
• Theoretical model accurately reproduced experimental results quantitatively and qualitatively.
• Unusual behavior of the resonance width due to mixed electronic character and geometry.

Conclusions:

• The study successfully elucidates the mechanism of dissociative electron attachment in HNCO.
• The identified A' resonance and the developed one-dimensional model provide a comprehensive understanding of the process.
• Isocyanic acid serves as a potential prototype for understanding DEA in other polyatomic systems.