Explicitly Correlated Coupled Cluster Calculations for Propadienylidene (H<sub>2</sub>CCC)

2010-09-16T00:00:00Z (GMT) by Peter Botschwina Rainer Oswald
Propadienylidene (H<sub>2</sub>CCC), a reactive carbene of interest to combustion processes and astrochemistry, has been studied by explicitly correlated coupled cluster theory at the CCSD(T)-F12x (x = a, b) level. Vibrational configuration interaction (VCI) has been employed to calculate accurate wavenumbers for the fundamental vibrations of H<sub>2</sub>CCC, D<sub>2</sub>CCC, and HDCCC. The symmetric CH stretching vibration of H<sub>2</sub>CCC is predicted to occur at ν<sub>1</sub> = 2984 cm<sup>−1</sup>. Absorptions observed by argon matrix infrared spectroscopy at 3049.5 and 3059.6 cm<sup>−1</sup> are reassigned to the combination tone ν<sub>2</sub> + ν<sub>4</sub>, which interacts with ν<sub>1</sub> and is predicted to have a higher intensity than the latter. Furthermore, IR bands detected at 865.4 and 868.8 cm<sup>−1</sup> are assigned to ν<sub>6</sub>(HDCCC), and those observed at 904.0 and 909.8 cm<sup>−1</sup> are assigned to the out-of-plane bending vibration ν<sub>8</sub>(HDCCC). An accurate value of 79.8 ± 0.2 kJ mol<sup>−1</sup> is recommended for the zero-point vibrational energy of H<sub>2</sub>CCC.