X-Ray Absorption Spectrum of the N_{2}^{+} Molecular Ion.

Area of Science:

• Atomic and Molecular Physics
• Quantum Chemistry
• Spectroscopy

Background:

• Understanding core-excited states of small molecules is crucial for chemical dynamics.
• Nitrogen molecular ion (N₂⁺) is a fundamental system for studying electronic structure.

Purpose of the Study:

• To measure and interpret the K-edge X-ray absorption spectrum of N₂⁺.
• To determine spectroscopic constants of specific core-excited states.
• To investigate electronic configuration mixing and double excitations.

Main Methods:

• Ion storage in a cryogenic radio frequency ion trap.
• Irradiation with synchrotron radiation for X-ray absorption spectroscopy.
• Restricted active space multiconfiguration self-consistent field (RAS-MCSCF) calculations.

Main Results:

• Experimental K-edge X-ray absorption spectrum of N₂⁺ was obtained.
• Spectroscopic constants for the 1σu⁻¹ ²Σu⁺ and two 1σu⁻¹3σg⁻¹1πg ²Πu states were determined.
• Evidence of significant configuration mixing and double excitations in higher-lying states.

Conclusions:

• The study provides detailed insights into the electronic structure of core-excited N₂⁺.
• RAS-MCSCF theory accurately reproduces experimental spectral features.
• Complex electronic interactions challenge simple orbital descriptions for these states.