Confirmation of pentavalent carbon in Protonated Methane (CH5+ ): Insights from Molecular Handycam Technique

The existence of pentavalent carbon has intrigued scientists since the discovery of CH5+ in 1952 but remains elusive due to the lack of definitive evidence. The present study unveils the mystery through a comprehensive investigation of the structural and bonding nature of CH5+ employing the newly developed Molecular Handycam technique (MHT) by Bag and co-workers, focusing on its formation pathways and energetic favorability. Computational analysis at the level of coupled-cluster theory (CCSD), we examine the formation of CH5+ through the association of CH3+ and H2 compared to the protonation of methane. Our findings reveal a preference for the former pathway, highlighting distinct structural configurations, including a global minimum and two alternative geometries. We demonstrate the participation of higher orbitals of carbon (3dz^2 ) and its interaction with the bond pair of the approaching H_2 molecule in forming and stabilizing the fifth C-H bond. This analytical approach provides critical insights into the expanded valency of carbon, which could lead to a new class of carbon compounds.