Multireference configuration interaction and quantum defect calculations on the Rydberg states of the BH molecule

The low-lying electronic states and optical schemes for the laser cooling of the BH+ and BH- ions

The potential energy curves and transition dipole moments for the 1²Σ⁺, 2²Σ⁺, 1²Π and 2²Π electronic states of the two molecules are calculated using multi-reference configuration interaction and the large basis sets aug-cc-pwCV5Z. Based on the obtained potential energy curves, the rotational and vibrational energy levels of the states are obtained by solving the Schrödinger equation of nuclear motion, and the spectroscopic parameters are then obtained by fitting the energy levels to Dunham series expansions. The spin-orbit coupling effect of the ²Π states for both the BH⁺ cation and BH^- anion are calculated. Highly diagonally distributed Franck-Condon factors are determined for the 1²Σ⁺ (v″=0)↔1²Π (v'=0) transition, ƒ₀₀ (BH⁺)=0.943, while the Franck-Condon factors for the 1²Π (v″=0)↔1²Σ⁺ (v'=0) transition is ƒ₀₀ (BH^-)=0.942. Moreover, the radiative lifetime of 38.2ns for the excited 1²Π state of the BH⁺ and 91.8ns for the 1²Σ⁺ state of the BH^- are obtained, which are short enough for rapid laser cooling. A three-step optical scheme of the laser cooling is constructed for either the BH⁺ cation or the BH^- anion.

Electronically Excited States of Borylenes

Borylenes, RB, are elusive reactive intermediates. Still not much is known about their excited states from spectroscopic experiments, and existing knowledge is limited to diatomic borylenes only. The electronic structure and geometry of borylenes with diverse substituents on boron (where R = H, F, Cl, CH3, CF3, tBu, NH2, Ph, and SiMe3) were studied by means of computational chemistry. For this purpose, geometries of borylenes in their lowest singlet and triplet states were optimized at the B3LYP/def2-TZVP level of theory. Additionally, the influence of substitution on the energies of frontier molecular orbitals, HOMO-LUMO energy gaps, singlet-triplet energy splittings, and excitation energies was investigated. Two lowest vertical singlet-singlet excitations were computed using EOM-CCSD and TD-DFT (using hybrid B3LYP, and long-range separated CAM-B3LYP and ωB97X functionals) in combination with the aug-cc-pVTZ basis set. The electronic transitions involve excitations from nonbonding sp boron orbital (HOMO) mainly to empty p(B) orbitals and partially to the orbitals of the substituent, and are of n → π* type. The results can facilitate prospective identification of borylenes, e.g., in UV-vis matrix isolation or time-resolved spectroscopy experiments.