Ab initio excitation spectrum of the weak H···CO interaction

摘要

The adiabatic interaction energy (IE) in the van der Waals region of the ground $ {text{H}}left( {{}^{2}{text{S}}} right) cdots {text{CO}}left( {{text{X}}^{1} Upsigma^{ + } } right) $ and excited $ {text{H}}left( {{}^{2}{text{S}}} right) cdots {text{CO}}left( {{text{a}}^{3} Uppi } right) $ electronic states of the $ {text{H}} cdots {text{CO}} $ complex is studied in the framework of the supermolecule approach at the RHF-CCSD(T) level of theory. Calculations predict a minimum with β e = 72°, R e = 6.89a o and D e = 34.10 cm?1 for the ground X2A′state. For the excited 4A′ state the minimum occurs at β e = 104° and R e = 5.90a o with D e = 75.42 cm?1. The resulting IE of the excited 4A′′ state reveals two minima separated by a saddle point. The most stable configuration occurs at β e = 132°, R e = 6.71a o and D e = 40.03 cm?1. The corresponding vertical excitation energies and corresponding shifts with respect to the isolated CO molecule are calculated as a guideline for future theoretical and experimental work. In order to investigate the use of less demanding correlation methods, test density functional theory calculations using the mPW1PW exchange–correlation functional are also presented for comparison.