ACCURATE FUNDAMENTAL FREQUENCIES AND SPECTROSCOPIC CONSTANTS FOR $CCH^{-}, NH^{-}_{2}$ AND THEIR ISOTOPOMERS
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Date
2003
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Ohio State University
Abstract
Accurate quartic force fields have been determined for the $CCH^{-}$ and $NH^{-}_{2}$ molecular anions using the singles and doubles coupled-cluster method that includes a perturbational estimate of the effects of connected triple excitations, CCSD(T). Very large one-particle basis sets have been used including diffuse functions and up through g-type functions. Correlation of the nitrogen and carbon core electrons has also been included. The fundamental vibrational frequencies have been computed using second-order perturbation theory and exact variational methods. Results for $NH^{-}_{2}$ are in excellent agreement with previous experiments, but for $CCH^{-}$ our results support low-resolution photoelectron experiments by Ervin and Lineberger that indicated the high-resolution studies by Gruebele, Polak, and Saykally error in their assignment for the CC stretch. The implications of our research for the astronomical observation of molecular anions will be discussed.
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Author Institution: MST27B-1, NASA Ames Research Center