Solid Parahydrogen Infrared Matrix Isolation and Computational Studies of Li_n-(C₂H₄)_m Complexes

Area of Science:

• Physical Chemistry
• Materials Science
• Quantum Chemistry

Background:

• Lithium-ethylene complexes are investigated for hydrogen storage applications.
• Two electronic states, 2A1 (van der Waals) and 2B2 (charge-transfer), exist for Li-(C2H4).
• The 2B2 state's strong dipole is key for binding hydrogen via electrostatic interactions.

Purpose of the Study:

• To resolve conflicting theoretical and experimental data on the ground electronic state of Li-(C2H4).
• To investigate the stability of Li-(C2H4) complexes under cryogenic conditions relevant to hydrogen storage.
• To characterize Li-ethylene complexes synthesized in solid parahydrogen.

Main Methods:

• Low-temperature synthesis of Li-n-(C2H4)-m complexes (n=1, m=1, 2).
• Infrared (IR) spectroscopy for characterization.
• Observation via the characteristic C=C stretching vibration of ethylene.

Main Results:

• The 2B2 electronic state of the Li-(C2H4) complex is found to be more stable under cryogenic conditions.
• Experimental evidence supports the 2B2 state's prevalence in solid parahydrogen.
• Successful synthesis and IR characterization of Li-(C2H4) and Li-(C2H4)2 complexes.

Conclusions:

• The Li-(C2H4) complex is stable in the advantageous 2B2 electronic state under cryogenic hydrogen storage conditions.
• This confirms its potential as an effective hydrogen storage material.
• The findings reconcile discrepancies between theoretical predictions and experimental observations.