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 C2P and CNP molecular systems an d their cations are studied. Geometries, harmonic frequencies, and dip ole moments have been obtained at the density functional (using the Be cke three-parameter Lee-Yang-Parr B3LYP functional) and coupled cluste r theoretical levels in conjunction with correlation consistent basis sets. Single-point coupled cluster calculations for B3LYP geometries h ave been used to compute energy differences for the different states. For the C2P radical, the global minimum is linear CCP((2) Pi) followed by cyclic C2P(B-2(2)) at 5.5 kcal/mol, linear CCP((4) Sigma(-)) (21.2 kcal/mol), cyclic C2P((4)A(2)) (38.4 kcal/mol), and linear CPC((2) Pi (g)) (88.0 kcal/mol). For the C2P+ cation the following sequence of st ates has been established: linear CCP+(1 Sigma(+)), cyclic C2P((1)A(1) ) (8.7 kcal/mol), cyclic C2P+(B-3(2)) (24.1 kcal/mol), linear CCP+((3) Pi) (29.1 kcal/mol), and linear CPC+((1) Sigma(g)(+)) (104.3 kcal/mol ). For neutral PCN and PNC, the following sequence of states has been computed: linear PCN((3) Sigma(-)); linear PNC((3) Sigma(-)) (14.2 kca l/mol), linear PCN(1 Delta) (25.2 kcal/mol), cyclic CPN((3)A'') (36.2 kcal/mol), cyclic CPN((1)A'') (37.7 kcal/mol), and linear PNC(1 Delta) (38.8 kcal/mol). The ground state of the single ionized species is li near PNC+((2) Pi) followed by linear PCN+((2) Pi); the energy differen ce is very small: 0.8-1.4 kcal/mol. Cyclic CPN+((2)A') lies much highe r 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/m ol for CCP((2) Pi) and 276.0 +/- 1 kcal/mol for PCN((3) Sigma(-)). Adi abatic ionization potentials (eV) areas follows: linear CCP((2) Pi) 9. 05, cyclic C2P(B-2(2)) 9.18, linear PCN((3) Sigma(-)) 10.39, and linea r PNC((3) Sigma(-)) 9.73.