Explicitly Correlated Coupled Cluster Calculations for Propadienylidene (H2CCC)

Propadienylidene (H2CCC), 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 H2CCC, D,CCC, and HDCCC. The symmetric CH stretching vibration of H2CCC is predicted to occur at v(1) = 2984 cm(-1). Absorptions observed by argon matrix infrared spectroscopy at 3049.5 and 3059.6 cm(-1) are reassigned to the combination tone v(2) + v(4), which interacts with vi and is predicted to have a higher intensity than the latter. Furthermore, IR bands detected at 865.4 and 868.8 cm(-1) are assigned to v(6)(HDCCC), and those observed at 904.0 and 909.8 cm(-1) are assigned to the out-of-plane bending vibration vs(HDCCC). An accurate value of 79.8 +/- 0.2 kJ mol(-1) is recommended for the zero-point vibrational energy of H2CCC.