Formylmethylene: The Triplet Ground State and the Lowest Singlet State

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• 作者：Jun Guan ; Katherine R. Randall ; Henry F. Schaefer ; III ; Huidong Li
• 刊名：The Journal of Physical Chemistry A
• 出版年：2013
• 出版时间：March 14, 2013
• 年：2013
• 卷：117
• 期：10
• 页码：2152-2159
• 全文大小：395K
• 年卷期：v.117,no.10(March 14, 2013)
• ISSN：1520-5215

文摘

The ground triplet state and lowest singlet state of formylmethylene have been proposed as important intermediates in the Wolff rearrangement of 伪-diazo ketones into ketenes. The ground triplet state of formylmethylene has been examined experimentally, but the lowest singlet state has yet to be observed. We predict equilibrium geometries, energies, bonding, dipole moments, and harmonic vibrational frequencies for these two lowest states of formylmethylene at the cc-pVQZ CCSD(T) level of theory. The singlet鈥搕riplet energy difference [螖E(S-T)] is quite sensitive to the level of theory. The highly accurate cc-pVQZ CCSD(T) level of theory yields the most reliable result of only 2.0 kcal mol^鈥?. An estimate based on the experimentally characterized CH₂ molecule yields 螖E(S-T) = 1.27 kcal mol^鈥?. In addition, accurate quartic force fields have been determined at the cc-pVTZ CCSD(T) level of theory. Fundamental vibrational frequencies, anharmonic constants, and vibration鈥搑otation coupling constants were determined using vibrational second-order perturbation theory (VPT2). Our results should aid in experimental detection and characterization of the lowest singlet state of formylmethylene, which is highly desirable for better understanding the mechanism of the Wolff rearrangement.