A theoretical study of the intermolecular interactions of H₂-CuF complex: Intermolecular vibrations, isotope effects,...

In this paper, a theoretical study has been made on the intermolecular interactions of the H₂-CuF complex, including binding energy, intermolecular vibrations, isotope effects, and rotational structure. Based on different bond lengths of H₂ and CuF monomers, three intermolecular potential energy surfaces (PESs) were constructed at the level of single and double excitation coupled-cluster method with a non-iterative perturbation treatment of triple excitations [CCSD(T)] with aug-cc-pVTZ basis set supplemented with bond functions. A global minimum on the PESs show that H₂-CuF complex belongs to C_2ν point group with a T-shaped structure. The obtained binding energy ranges from 8890 to 10050 cm^-1, which increases as the increment of H-H bond length, but opposite case has been determined as the increment of Cu-F bond length. The accuracy of PESs was examined by the available data of 1₀₁-0₀₀ transition. The predicted rotational transition frequency obtained from bound state calculations can reproduce the experimental observation very well, and the predicted error is 0.1% based on the PES1 constructed with r_H2 and r_CuF fixed at 0.838 and 1.7409 Å. By analyzing the wave function of the bound state, the intermolecular vibrational modes were assigned unambiguously. Isotope effects were also studied and the largest error is also 0.1% compared with the available 1₀₁-0₀₀ transition data. A set of spectroscopic parameters were obtained for six isotopologues to determine rotational structure of H₂-CuF complex. Upon the complex formation, the obtained structure parameters show that H-H bond length is elongated by 0.081 Å, while Cu-F value is shortened by 0.008 Å from the respective average bond lengths of free monomer.