Ab initio calculation on the low-lying excited states of cation including spin–orbit coupling

The Electronic Spectrum of Si2+

“…A complete list of observed peaks and their assignments is given in Table S1 in the Supporting Information (SI). The observed peaks allow a determination of the harmonic frequencies and anharmonicity constants of the ground and excited electronic states via a fit to the Dunham expression to ω″ = 472(2) cm –1 , ω′ = 366(3) cm –1 , ω″χ″ = 2.4(4) cm –1 , and ω′χ′ = 7.6(4) cm –1 , which show an astonishing agreement with the calculated values obtained at previous ab initio all-electron relativistic calculations at the MRCI+Q/AVQZ level (Table ) and thus confirm the assignment of the excited state and shape of the PECs. Our time-dependent density functional theory (TD-DFT) calculations at the CAM-B3LYP/cc-PVQZ level of theory cannot reproduce the properties of the 4 Σ u – (I) state, probably due to interaction with other close lying states.…”

“…PDC measurements of the larger silicon cluster cations (Si n + , n ≥ 6) also show similarly unstructured spectra . Theoretically, it is predicted that Si 2 + has a 4 Σ g – ground state with a ...4σ g αβ 4σ u αβ 2π u αα 5σ g α electron configuration. ,, Several excited states have been predicted to understand Si 2 + , or to assist in the determination of the ionization energy of Si 2 . Several molecular constants were predicted that can now be compared for the first time to experimental results, which allow confirmation of previous theoretical electronic configuration assignments of the complex electronic structure of Si 2 + (shown in Figure S1).…”

“…Successively, more and more band systems were identified and assigned by ab initio calculations − (and references therein). Here, we present the first description of two band systems of Si 2 + , providing valuable insight into the geometric and electronic structure of this simple diatomic cation of fundamental interest in molecular physics, which still provides a challenge for its theoretical description. , Apart from its fundamental importance, the optical spectrum of Si 2 + may also enable astrophysical searches for this potential building block of interstellar silicate dust, and detailed knowledge about the excited-state potential energy curves (PEC) may assist in understanding possible multistate reactivity of Si 2 + . , …”

“…Several molecular constants were predicted that can now be compared for the first time to experimental results, which allow confirmation of previous theoretical electronic configuration assignments of the complex electronic structure of Si 2 + (shown in Figure S1). , …”

“…The 4 Σ u – (I) ← X 4 Σ g – band system observed near 430 nm is shown in Figure . Due to the high dissociation energy of Si 2 + of 3.628 eV (29 278 cm –1 ), the whole band is observed after resonant multiphoton absorption. The given cross section is calculated, without claiming correctness, assuming a two-photon absorption process with the second photon having an absorption probability of 1.…”