High accuracy ab initio methods applied to phosphaethyne and perchlorosilylcarbene

High-accuracy ab initio methods have been applied to two chemical systems: phosphaethyne (HCP) and perchlorosilylcarbene (Cl-C-SiCl3). HCP and its isomerization species linear HPC (found to be a second-order saddle point) have been characterized at couple cluster levels with triple contributions [CCSD(T), CCSDT-3, CC3] and a large correlation consistent basis set, cc-pV5Z. Eight singlet excited states were examined and characterized using the equation-of-motion coupled cluster method. For perchlorosilylcarbene, the potential energy surface was determined by optimizing three stationary points on both the singlet and triplet surfaces, including a focal-point analysis to nail down the relative energy differences. The infrared spectrum was predicted for each minima to help in determining the nature of the species trapped by Schreiner, et. al. The global minimum and the best fit for the infrared spectrum was the triplet carbene species, in line with previous experimental and theoretical work on analogous systems.