Anharmonicity of Weakly Bound Li+–(H2)n (n = 1–3) Complexes

The anharmonicity of Li(+)-(H(2))(n) (n = 1, 2, and 3) complexes is studied using the vibrational self-consistent field (VSCF) approach. The H-H stretching frequency shifts of Li(+)-(H(2))(n) complexes are calculated with the coupled-cluster method including all single and double excitations with perturbative triples (CCSD(T)) level of theory with the cc-pVTZ basis set. The calculated IR active H-H stretching frequency in Li(+)-H(2), Li(+)-(H(2))(2) and Li(+)-(H(2))(3) is red-shifted by 121, 109, and 96-99 cm(-1), respectively, relative to that of isolated H(2). The calculated red shifts and their trends are in good agreement with the available experimental data.