Characterization of the Ground and Several Low-Lying Singlet Exicted States of HCP
Justin B. Ingels, Justin M. Turney, Yukio Yamaguchi, Henry F. Schaefer III
The ground (1Σ+) and excited states
(1Σ-, 1Δ, 1A’, 1A”) of HCP have been systematically
investigated using a variety of ab initio methods. For the ground state, two linear stationary points have
been optimized and physical properties determined utilizing restricted Hartree-Fock theory (RHF),
coupled cluster theory with single and double excitations (CCSD), perturbative triples corrections
[CCSD(T)], and iterative triples approaches (CCSDT-3, CC3). The only stable minimum found on the
ground state surface was linear HCP. Physical properties determined for this state include harmonic
vibrational frequencies at cc-pVQZ CCSD(T) of ω1 = 3345 cm-1,
ω2 = 687 cm-1, and ω3 = 1295 cm-1,
and a dipole moment of 0.454 Debye. Linear HPC, a second-order saddle point, is predicted to lie
74.9 kcal mol-1 above the global minimum HCP. The dissociation energy to H(2S)
and CP(2Σ+), D0, of HCP has been determined to be 118.6 kcal mol-1.
Six excited states were examined and their physical properties determined utilizing three equation-of-motion
coupled cluster methods (EOM-CCSD, EOM-CCSDT-3, EOM-CC3). For the lowest-lying excited surface,
1Σ+ → 1Σ-, three stationary points were
optimized with excitation energies, Te, of 101.2 kcal mol-1 (1A”),
104.5 kcal mol-1 (1A”), and 122.4 kcal mol-1 (1Σ-)
at cc-pVQZ EOM-CC3. The physical properties of the 1A” state with a bond angle of 129.4 degrees
compares well with the experimentally reported first singlet state . For the second lowest lying singlet excited
surface, 1Σ- → 1Δ, three stationary points were found with
Te values of 110.5 kcal mol-1 (1A’), 112.3 kcal mol-1
(1A’), and 125.5 kcal mol-1 (1Δ).
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