Potential Energy Curves of the Low-Lying Five 1Σ+ and 1Π States of a CH+ Molecule Based on the Free Complement - Local Schrodinger Equation Theory and the Chemical Formula Theory

The potential energy curves (PECs) of the low-lying five (1)Sigma(+) and (1)Pi states (X-1 Sigma(+), C-1 Sigma(+), 3(1)Sigma(+), A(1)Pi, and D-1 Pi states) of a CH+ molecule, an important interstellar molecule, were calculated by the free complement (FC) local Schrodinger equation (LSE) theory with the direct local sampling scheme. The FC wave functions were constructed based on the chemical formula theory (CFT), whose local characters correspond to the covalent dissociations: C+(P-2 degrees(s(2)p))) + H(S-2) of the X-1 Sigma(+) and A(1)Pi states and the ionic dissociations: C(D-1(s(2)p(2))) + H+ of the C-1 Sigma(+) and D-1 Pi states. All the calculated PECs were obtained with satisfying the chemical accuracy, i.e., error less than 1 kcal/mol, as absolute total energy of the Schrodinger equation without any energy shift. The spectroscopic data calculated from the PECs agreed well with both experimental and other accurate theoretical references. We also analyzed the wave functions using the inverse overlap weights proposed by Gallup et al. with the CFT configurations. For the X-1 Sigma(+) and A(1)Pi states, the covalent C+(sp2) and C+(p3) configurations played important roles for bond formation. In the small internuclear distances of the C-1 Sigma(+), D-1 Pi, and 3(1)Sigma(+) states, the covalent character was also dominant as a result of the electron charge transfer from C to H+. Thus, the present FC-LSE results not only are accurate but also can provide chemical understanding according to the CFT.

Automated summary

This study used the free complement local Schrodinger equation theory with the direct local sampling scheme to calculate the potential energy curves (PECs) and spectroscopic data of the low-lying states of a CH+ molecule. The calculated PECs agreed well with experimental and theoretical references. The analysis of wave functions revealed the important roles of covalent configurations in bond formation and the dominant covalent character in ion dissociation.