Photodissociation and Infrared Spectroscopy of Uranium-Nitrogen Cation Complexes

Area of Science:

• Physical Chemistry
• Inorganic Chemistry
• Spectroscopy

Background:

• Uranium complexes with nitrogen are not well understood.
• Investigating the bonding and structure of uranium-nitrogen complexes is crucial for fundamental chemical knowledge.

Purpose of the Study:

• To synthesize and characterize uranium-nitrogen (U⁺(N₂)_n) complexes.
• To determine the bonding characteristics and dissociation energies of these complexes.
• To compare experimental findings with theoretical predictions.

Main Methods:

• Laser vaporization of uranium in a nitrogen supersonic expansion.
• Mass selection using a reflectron time-of-flight spectrometer.
• Photodissociation spectroscopy (visible, UV, and tunable IR lasers).
• Density functional theory (DFT) calculations.

Main Results:

• U⁺(N₂)_n complexes (n=1-8) were successfully produced.
• Nitrogen ligands remain intact molecules, with no evidence of insertion chemistry.
• Average U⁺-N₂ bond dissociation energy was estimated at 12 kcal/mol.
• Infrared spectroscopy showed red-shifted N-N vibrations, indicating interaction with U⁺.
• DFT predicted a stable sextet state for U⁺ and end-on binding of N₂, with a cubic structure for U⁺(N₂)₈.

Conclusions:

• The U⁺-N₂ bond is relatively weak and consistent across different coordination numbers.
• Experimental and theoretical results for bond dissociation energy show good agreement.
• DFT calculations provide insights into the structure and electronic state of the complexes, despite discrepancies in vibrational frequencies.