Wigner Near-Threshold Effects in the Photoelectron Angular Distribution of NO₂

Area of Science:

• Physical Chemistry
• Molecular Spectroscopy
• Quantum Chemistry

Background:

• The nitrite anion (NO2-) is a key molecule in atmospheric and combustion chemistry.
• Understanding its electronic structure is crucial for predicting its reactivity.
• Previous studies have lacked detailed information on its ground state properties.

Purpose of the Study:

• To investigate the electronic and vibrational structure of the nitrite anion (NO2-).
• To determine the spectroscopic constants of the NO2- anion and NO2 neutral molecule.
• To analyze the photoelectron angular distributions and their dependence on kinetic energy.

Main Methods:

• High-resolution velocity map imaged photoelectron spectroscopy.
• Photodetachment experiments using wavelengths from 355 to 550 nm.
• Construction of a rotational band model for spectral analysis.

Main Results:

• Resolved vibrational and rotational structure of the NO2- photodetachment transition.
• Measured photoelectron angular distribution parameter (β) ranging from 1.5 to 1.7.
• Observed a dramatic drop in β to 0 near the detachment threshold, explained by Wigner near-threshold laws.
• Developed a mixed spd orbital model for NO2- with 2% p, 44% s, and 54% d character.

Conclusions:

• The study provides a comprehensive understanding of the NO2- electronic and vibrational states.
• Wigner near-threshold laws significantly influence electron detachment dynamics.
• The determined molecular orbital composition offers insights into the anion's bonding and reactivity.