BeCH2: The Simplest Metal Carbene. High Levels of Theory

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• 作者：Yudong Qiu ; Alexander Yu. Sokolov ; Yukio Yamaguchi ; Henry F. Schaefer ; III
• 刊名：Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：September 26, 2013
• 年：2013
• 卷：117
• 期：38
• 页码：9266-9273
• 全文大小：311K
• 年卷期：v.117,no.38(September 26, 2013)
• ISSN：1520-5215

文摘

The simplest metal carbene, BeCH₂, is experimentally unknown. Its isomer, HBeCH, lies higher in energy, but has been detected by the infrared matrix isolation [J. Am. Chem. Soc. 1998, 120, 6097]. In the present study the ground and low-lying excited states of the BeCH₂ and HBeCH isomers were investigated using state-of-the-art ab initio methods, including coupled-cluster theory with up to full quadruple excitations (CCSDTQ), and complete active space self-consistent field (CASSCF) with multireference configuration interaction with single and double excitations (MRCISD). The relative energies were obtained using the focal point analysis combined with large correlation-consistent cc-pCVXZ basis sets (X = D, T, Q, 5) and were extrapolated to the complete basis set (CBS) limit. The ³B₁ state of BeCH₂ (C_2v symmetry) is the global minimum on the ground triplet potential energy surface (PES). The ³危^{鈥?/sup> state of the linear isomer HBeCH is located 4.9 kcal mol鈥? above the global minimum, at the CCSDTQ/CBS level of theory. The BeCH₂ and HBeCH isomers are connected through the 3A鈥?transition state lying 46.1 kcal mol鈥? above the global minimum. The higher-lying energy HBeCH structure has much larger Be鈥揅 bond dissociation energy (126.6 kcal mol鈥?, cf. BDE(BeCH₂) = 62.1 kcal mol鈥?). The lowest excited state of BeCH₂ is the open-shell 1B₁ state, with a relative energy of only 4.9 kcal mol鈥? above the global minimum, followed by 1A₁ state (16.8 kcal mol鈥?) at the MRCISD/cc-pCVQZ level of theory. For the HBeCH isomer the lowest-energy excited states are 1螖 and 1危+, lying about 30 kcal mol鈥? above the global minimum. For the ground state of BeCH₂ the fundamental vibrational frequencies computed using second-order vibrational perturbation theory (VPT2) at the CCSD(T)/cc-pCVQZ level are reported. We hope that our highly accurate theoretical results will assist in the experimental identification of BeCH₂.}