Application of equation-of-motion coupled-cluster methods to low-lying singlet and triplet electronic states of HBO and BOH

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The equilibrium structures and physical properties of the X̃ ∑+1 linear electronic states, linear excited singlet and triplet electronic states of hydroboron monoxide (HBO) (à ∑-1, B̃ Δ1, ã ∑+3, and b̃ Δ3) and boron hydroxide (BOH) (à ∑+1, B̃ Π1, and b̃ Π3), and their bent counterparts (HBO ã A′3, b̃ A″3, à A″1, B̃ A′1 and BOH X̃ A′1, b̃ A′3, c̃ A″3, à A′1, B̃ A′1, C̃ A″1) are investigated using excited electronic state ab initio equation-of-motion coupled-cluster (EOM-CC) methods. A new implementation of open-shell EOM-CC including iterative partial triple excitations (EOM-CC3) was tested. Coupled-cluster wave functions with single and double excitations (CCSD), single, double, and iterative partial triple excitations (CC3), and single, double, and full triple excitations (CCSDT) are employed with the correlation-consistent quadruple and quintuple zeta basis sets. The linear HBO X̃ ∑+1 state is predicted to lie 48.3 kcal mol-1 (2.09 eV) lower in energy than the BOH X̃ ∑+1 linear stationary point at the CCSDT level of theory. The CCSDT BOH barrier to linearity is predicted to lie 3.7 kcal mol-1 (0.16 eV). With a harmonic zero-point vibrational energy correction, the HBO X̃ ∑+1 -BOH X̃ A′1 energy difference is 45.2 kcal mol-1 (1.96 eV). The lowest triplet excited electronic state of HBO, ã A′3, has a predicted excitation energy (Te) of 115 kcal mol-1 (4.97 eV) from the HBO ground state minimum, while the lowest-bound BOH excited electronic state, b̃ A′3, has a Te of 70.2 kcal mol-1 (3.04 eV) with respect to BOH X̃ A′1. The Te values predicted for the lowest singlet excited states are à A″1 ← X̃ ∑+1 =139 kcal mol-1 (6.01 eV) for HBO and à A′1 ← X̃ A′1 =102 kcal mol-1 (4.42 eV) for BOH. Also for BOH, the triplet vertical transition energies are b̃ A′3 ← X̃ A′1 =71.4 kcal mol-1 (3.10 eV) and c̃ A″3 ← X̃ A′1 =87.2 kcal mol-1 (3.78 eV). © 2005 American Institute of Physics.



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Journal of Chemical Physics





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