Barrier To Linearity and Anharmonic Force Field of the Ketenyl Radical
Andrew C. Simmonett
Nathan J. Stibrich
Brian N. Papas
Henry F. Schaefer
Wesley D. Allen
10.1021/jp9024365.s001
https://acs.figshare.com/articles/journal_contribution/Barrier_To_Linearity_and_Anharmonic_Force_Field_of_the_Ketenyl_Radical/2817559
The troublesome barrier to linearity of the ketenyl radical (HCCO) is precisely determined using state-of-the-art computations within the focal point approach, by combining complete basis set extrapolation, utilizing the aug-cc-pV<i>X</i>Z (<i>X</i> = D, T, Q, 5, 6) family of basis sets, with electron correlation treatments as extensive as coupled cluster theory with single, double, triple, and perturbative quadruple excitations [CCSDT(Q)]. Auxiliary terms such as diagonal Born−Oppenheimer corrections (DBOCs) and relativistic contributions are included. To gain a definitive theoretical treatment and to assess the effect of higher-order correlation on the structure of HCCO, we employ a composite approximation (c∼) to all-electron (AE) CCSDT(Q) theory at the complete basis set (CBS) limit for geometry optimizations. A final classical barrier to linearity of 630 ± 30 cm<sup>−1</sup> is obtained for reaching the <sup>2</sup>Π Renner−Teller configuration of HCCO from the <sup>2</sup>A′′ ground state. Additionally, we compute fundamental vibrational frequencies and other spectroscopic constants by application of second-order vibrational perturbation theory (VPT2) to the full quartic force field at the AE-CCSD(T)/aug-cc-pCVQZ level. The resulting (ν<sub>1</sub>, ν<sub>2</sub>, ν<sub>5</sub>) fundamental frequencies of (3212, 2025, 483) cm<sup>−1</sup> agree satisfactorily with the experimental values (3232, 2023, 494) cm<sup>−1</sup>.
2009-10-29 00:00:00
cm
DBOC
CCSDT
electron correlation treatments
frequency
HCCO
barrier
point approach
Anharmonic Force Field
CBS
vibrational frequencies
cluster theory
Ketenyl RadicalThe
geometry optimizations
vibrational perturbation theory
basis sets
linearity
VPT
2Π
quartic force field
AE
spectroscopic constants