An ab initio study of the electronic structure of BF and BF+

Photoelectron spectroscopy of boron-containing reactive intermediates using synchrotron radiation: BH2, BH, and BF

Mass selected slow photoelectron spectra (SPES) of three boron-containing reactive species, BH₂, BH, and BF were recorded by double imaging photoion-photoelectron coincidence spectroscopy (i²PEPICO) using synchrotron radiation. All species were generated in a flow reactor from the H-abstraction of B₂H₆ by F atoms created in a F₂ microwave discharge. The spectrum of BH₂⁺ exhibits a long bending mode progression with a 970 cm^-1 spacing due to the large geometry change from bent to linear upon ionization. Its ionization energy was determined as 8.12 ± 0.02 eV. For BH, photoionisation from both X¹Σ⁺ singlet and a³Π triplet state was observed, permitting the experimental determination of the singlet/triplet gap (ΔE_ST) from the observed IE's of 9.82 eV and 8.48 eV. In addition, a threshold photoelectron spectrum of BF was recorded, which leads to an IE of 11.11 eV and an improved value for ν_BF⁺ of 1690 cm^-1. All spectra were simulated by calculating Franck-Condon factors from optimised structures based on quantum chemical calculations.

Bond Order Densities in Real Space

In this contribution we introduce the concept of bond order density (BOD) on the basis of a previous work on natural adaptive orbitals. We show that BODs may be used to visualize both the global spatial distribution of the covalent bond order and its eigencomponents, which we call bond(ing) channels. BODs can be equally computed at correlated and noncorrelated levels of theory and in ground or excited states, thus offering an appealing description of bond-forming, bond-breaking, and bond-evolution processes. We show the power of the approach by examining a number of homo- and heterodiatomics, including the controversial existence of a fourth bonding component in dicarbon, by analyzing a few interesting bonding situations in polyatomics and chemical transformations, and by exemplifying exotic bonding behaviors in simple excited electronic states.

Accurate spectroscopic calculations of the 14Λ-S and 30Ω states of BF+ cation including the spin-orbit coupling effect

This paper studied the potential energy curves of 30Ω states yielded from the 14Λ-S states (X²Σ⁺, 1²Π, 2²Π, 3²Π, 1²Σ^-, 2²Σ⁺, 3²Σ⁺, 1²Δ, 1⁴Σ^-, 1⁴Σ⁺, 2⁴Σ⁺, 1⁴Π, 2⁴Π, and 1⁴Δ) of the BF⁺ cation. The potential energy curves were calculated for internuclear separations from approximately 0.08 to 1.1nm using the CASSCF method, which was followed by the icMRCI approach with the aug-cc-pV6Z basis set. Of these 14Λ-S states, the 2⁴Σ⁺ and 2⁴Π states were repulsive. The 2²Π and 3²Π states had double wells. The avoided crossings were found between the 1²Π and the 2²Π state, and between the 3²Π and the 4²Π state. The 1²Π, 2²Π, 3²Π, and 1⁴Π states were inverted with the spin-orbit coupling effect taken into account. The 1⁴Π state and the second wells of 2²Π and 3²Π states were weakly bound. Each of the 1²Π, 2²Π, and 3²Π states had one barrier. The potential energy curves of all the Λ-S and Ω states were extrapolated to the complete basis set limit. Core-valence correlation and scalar relativistic corrections were included at the level of an aug-cc-pV5Z basis set. The spin-orbit coupling effect was included by the state interaction approach with the Breit-Pauli Hamiltonian and the all-electron cc-pCV5Z set. The spectroscopic parameters were determined and compared with available experimental and other theoretical ones. The spin-orbit coupling effect on the spectroscopic parameters was evaluated in detail. Comparison with available experimental data show that the methodology used in this paper is highly accurate for this system.

Term rules for simple metal clusters

Hund’s term rules are only valid for isolated atoms, but have no generalization for molecules or clusters of several atoms. We present a benchmark calculation of Al₂ and Al₃, for which we find the high and low-spin ground states ³Π_u and , respectively. We show that the relative stabilities of all the molecular terms of Al₂ and Al₃ can be described by simple rules pertaining to bonding structures and symmetries, which serve as guiding principles to determine ground state terms of arbitrary multi-atom clusters.

Nature of the chemical bond and origin of the inverted dipole moment in boron fluoride: a generalized valence bond approach

The generalized product function energy partitioning (GPF-EP) method has been applied to investigate the nature of the chemical bond and the origin of the inverted dipole moment of the BF molecule. The calculations were carried out with GPF wave functions treating all of the core electrons as a single Hartree-Fock group and the valence electrons at the generalized valence bond perfect-pairing (GVB-PP) or full GVB levels, with the cc-pVTZ basis set. The results show that the chemical structure of both X (1)Σ(+) and a (3)Π states is composed of a single bond. The lower dissociation energy of the excited state is attributed to a stabilizing intraatomic singlet coupling involving the B 2sp-like lobe orbitals after bond dissociation. An increase of electron density on the B atom caused by the reorientation of the boron 2sp-like lobe orbitals is identified as the main responsible effect for the electric dipole inversion in the ground state of BF. Finally, it is shown that π back-bonding from fluorine to boron plays a minor role in the electron density displacement to the bonding region in both states. Moreover, this effect is associated with changes in the quasi-classical component of the electron density only and does not contribute to covalency in either of the states. Therefore, at least for the case of the BF molecule, the term back-bonding is misleading, since it does not contribute to the bond formation.