Structure and Vibrations of the C2P and CNP Radicals and Their Cations Using Density Functional and Coupled Cluster Theories

Energetically low-lying states of the C 2 P and CNP molecular systems and their cations are studied. Geometries, harmonic frequencies, and dipole moments have been obtained at the density functional (using the Becke three-parameter Lee−Yang−Parr B3LYP functional) and coupled cluster theoretical levels in conjunction with correlation consistent basis sets. Single-point coupled cluster calculations for B3LYP geometries have been used to compute energy differences for the different states. For the C 2 P radical, the global minimum is linear CCP( 2 Π) followed by cyclic C 2 P( 2 B 2 ) at 5.5 kcal/mol, linear CCP( 4 Σ - ) (21.2 kcal/mol), cyclic C 2 P( 4 A 2 ) (38.4 kcal/mol), and linear CPC( 2 Π g ) (88.0 kcal/mol). For the C 2 P + cation the following sequence of states has been established: linear CCP + ( 1 Σ + ), cyclic C 2 P( 1 A 1 ) (8.7 kcal/mol), cyclic C 2 P + ( 3 B 2 ) (24.1 kcal/mol), linear CCP + ( 3 Π) (29.1 kcal/mol), and linear CPC + ( 1 Σ + g ) (104.3 kcal/mol). For neutral PCN and PNC, the following sequence of states has been computed: linear PCN( 3 Σ - ); linear PNC( 3 Σ - ) (14.2 kcal/mol), linear PCN( 1 Δ) (25.2 kcal/mol), cyclic CPN( 3 A‘‘) (36.2 kcal/mol), cyclic CPN( 1 A‘‘) (37.7 kcal/mol), and linear PNC( 1 Δ) (38.8 kcal/mol). The ground state of the single ionized species is linear PNC + ( 2 Π) followed by linear PCN + ( 2 Π); the energy difference is very small: 0.8−1.4 kcal/mol. Cyclic CPN + ( 2 A‘) lies much higher in energy (13.9 kcal/mol) and was found to be a local energy minimum at the doublet surface. Predictions for IR spectra of the species are given. The computed total atomization energies are 261.7 ± 1 kcal/mol for CCP( 2 Π) and 276.0 ± 1 kcal/mol for PCN( 3 Σ - ). Adiabatic ionization potentials (eV) are as follows: linear CCP( 2 Π) 9.05, cyclic C 2 P( 2 B 2 ) 9.18, linear PCN( 3 Σ - ) 10.39, and linear PNC( 3 Σ - ) 9.73.