Silylidene (SiCH2) and its isomers: Anharmonic rovibrational analyses for silylidene, silaacetylene, and silavinylidene

Three equilibrium structures and two associated isomerization transition states for the SiCH2–HSiCH–CSiH2 system have been theoretically investigated using highly correlated ab initio methods combined with the correlation-consistent polarized core-valence basis sets. Vibrational second-order perturbation theory (VPT2) has been employed to obtain the zero-point vibration corrected rotational constants, centrifugal distortion constants, and fundamental vibrational frequencies for each equilibrium structure. The comparison of the theoretically predicted rotational constants and fundamental frequencies for silylidene (SiCH2) with existing experimental observations shows excellent agreement. The CH2 (CD2) rocking modes (ν6) are the most anharmonic among the six vibrational modes, consistent with limited experimental observations. The five stationary point structures and their relative energies on the ground state potential energy surface (PES) are accurately determined using the focal point extrapolation technique. Silylidene (SiCH2) has been confirmed to be the global minimum. Silaacetylene (HSiCH) with a trans-bent structure is located 34.8 ± 0.3 kcal mol−1 (with zero-point vibrational energy, scalar relativistic effects, and DBOC corrections) above the global minimum. The barrier height for the critical reverse isomerization process [HSiCH → SiCH2] is predicted to be 4.1 ± 0.3 kcal mol−1. The third isomer silavinylidene (CSiH2) is predicted to lie 84.6 ± 0.3 kcal mol−1 above the global minimum, with the barrier height for the reverse isomerization process [CSiH2 → HSiCH] being only 2.6 ± 0.3 kcal mol−1. The present research should assist the future experimental characterization of silylidene (SiCH2) isomers.

► The potential energy surface for SiCH2 system has been accurately established.
► The B0 rotational constants for SiCH2 and its isotopologues have been evaluated.
► The fundamental vibrational frequencies for SiCH2 system have been predicted.
► The theoretical predictions of frequencies are in accord with experimental results.