Theoretical Investigations on CaO Ions: Vibronic States and Photoelectron Spectroscopy

Abstract

The low-lying electronic states, X(2)Π and A(2)Σ(+) of CaO(+) and X(2)Σ(+) and A(2)Π of CaO(-), have been determined at the MRCI+Q level of theory with the aug-cc-pV5Z(O) and cc-pCV5Z(Ca) basis sets. The two states of CaO(+) are close within <0.1 eV and coupled via spin-orbit effect. The X(2)Σ(+) and A(2)Π states of CaO(-) are energetically separated by <1 eV such that the first excited state is close to the electronic ground state of neutral CaO and unstable with respect to electron detachment. Using the potential energy curves and the spin-orbit coupling terms, the vibronic energy levels of these ions have been determined. The ionization energy and the electron affinity of CaO are calculated at 6.79 and 0.79 eV, respectively. The photoelectron spectra of CaO(-) and CaO have also been simulated.

Near UV bands of jet-cooled CaO

“…As an example, the first excited singlet state is A' 1 , which arises from the X -1 configuration. There have been several high-level theoretical studies of the electronic states of CaO [15][16][17][18][19][20][21], mostly focused on the ground and low-lying excited states. Overall, the electronic structure calculations support the atomic-ions-in-molecules model of Field and co-workers [12].…”