Test Study on the Excitation Spectrum of the CO ⃛Ar van der Waals Molecule

Abstract

In the present contribution, we performed ab initio Møller-Plesset perturbation theory second-order (MP2) calculations in the framework of the supermolecule approach on the vertical excitation spectra of the weakly bound van der Waals CO-Ar molecule in its "near T-shaped" most stable ground state structure, as a guideline for future theoretical and experimental work. These test calculations indicate a ground CO ( X 1 D )- Ar ( 1 S ) interaction with R e =3.72 Å, D e =109 cm -1 and D o =92 cm -1 . They also indicate an excited CO ( A 1 @ )- Ar ( 1 S ) interaction with R e =3.55 Å, D e =141 cm -1 and D o =121 cm -1 . A red shift of 29 cm -1 for the CO ( X 1 D )- Ar ( 1 S ) M CO ( A 1 @ )- Ar ( 1 S ) vertical excitation energy, with respect to the corresponding CO ( X 1 D ) M CO ( A 1 @ ) excitation in the absence of Ar, can be obtained by comparing the corresponding D o values.