Real space atomic decomposition of fundamental properties of carbon monoxide in the ground and the two lowest lying excited electronic states ¹

¹This paper is dedicated to Professor André D. Bandrauk, PhD, Officer of the Order of Canada, FRSC, FAAAS, FAPS, FCIC, FSIAM, of the Université de Sherbrooke, on the occasion of his 75th birthday.

ABSTRACT

The properties of carbon monoxide in its ground and two lowest lying excited states are investigated by conventional and time-dependent (TD) density functional theory (DFT). The dipole moment is decomposed into atomic polarisation (AP) and inter-atomic charge transfer (CT) contributions according to the quantum theory of atoms in molecules (QTAIM). Considerable AP and CT contributions cancel in the ground state (S ₀) resulting in its known negligible dipole moment. This balance is disturbed in the lowest triplet (T ₁) and singlet (S ₁) excited states, resulting in dipole moments of 1.57 D for T ₁ and 0.49 D for S ₁ . The AP decreases by 2.5 D on excitation to either state but the opposing CT is reduced by 0.8 D for T ₁ and by 1.8 D for S ₁, insufficient for cancellation. These excitations induce charge transfer from O to C which drives dipole changes accompanied by a weakening of the C–O bond, more pronounced in the S ₁ state, as trends in bond lengths, vibrational frequencies, and QTAIM properties suggest. The charge–charge flux–dipole flux (CCFDF) model in terms of QTAIM parameters reveals that the vibrational stretching band weakening on excitation is predominantly due to changes in atomic charges.

KEYWORDS:

• Excited electronic states
• quantum theory of atoms in molecules (QTAIM)
• charge–charge flux–dipole flux (CCFDF) model
• time-dependent density functional theory (TD-DFT)
• excited state dipole moment

Acknowledgments

Luiz Alberto Terrabuio thanks CAPES for a doctoral fellowship and CNPq (Science without Borders Scholarship Program – 205445/2014-4) and for a visiting graduate studentship at Mount Saint Vincent University. Natieli Alves da Silva acknowledges CAPES for a doctoral fellowship. Roberto Luiz Andrade Haiduke thanks FAPESP for financial support (grants 2014/23714-1 and 2010/18743-1, São Paulo Research Foundation) and CNPq for a research grant (305366/2015-7). Chérif F. Matta acknowledges the funding of the Natural Sciences and Engineering Research Council of Canada (NSERC), Canada Foundation for Innovation (CFI), and Mount Saint Vincent University for financial support.

Disclosure statement

No potential conflict of interest was reported by the authors.

Additional information

Funding

Roberto Luiz Andrade Haiduke thanks FAPESP for financial support [grant number 2014/23714-1]; [grant number 2010/18743-1] (São Paulo Research Foundation) and CNPq for a research grant [number 305366/2015-7]. Chérif F. Matta acknowledges the funding of the Natural Sciences and Engineering Research Council of Canada (NSERC) [grant number RDPIN-2015-03731]; Canada Foundation for Innovation (CFI) [Project No. 18538]; Mount Saint Vincent University for financial support.