Anharmonicity of weakly bound Li(+)-(H2)n (n = 1-3) complexes

Area of Science:

• Physical Chemistry
• Computational Chemistry
• Spectroscopy

Background:

• Anharmonicity in molecular vibrations is crucial for understanding chemical interactions.
• Lithium ion complexes with hydrogen molecules provide a model system for studying ion-molecule interactions.

Purpose of the Study:

• To investigate the anharmonicity of Li+-(H(2))(n) complexes for n = 1, 2, and 3.
• To calculate the H-H stretching frequency shifts in these complexes and compare them with experimental results.

Main Methods:

• Utilizing the vibrational self-consistent field (VSCF) approach to study anharmonicity.
• Employing the coupled-cluster method with all single and double excitations and perturbative triples (CCSD(T)) level of theory.
• Using the cc-pVTZ basis set for high-accuracy calculations.

Main Results:

• Calculated red shifts in the IR active H-H stretching frequency for Li+-H(2), Li+-(H(2))(2), and Li+-(H(2))(3) were 121 cm(-1), 109 cm(-1), and 96-99 cm(-1), respectively.
• The observed red shifts relative to isolated H(2) demonstrate the influence of the lithium ion.
• The calculated trends in frequency shifts align well with available experimental data.

Conclusions:

• The VSCF and CCSD(T) methods accurately predict the vibrational frequency shifts in Li+-(H(2))(n) complexes.
• The study confirms the significant impact of the lithium ion on the H-H bond vibration within these complexes.
• Computational findings support experimental observations, validating the theoretical approach for similar systems.