A computational study of the HCCO and HCCS radicals

Abstract

The equilibrium geometries of the lowest electronic states of the HCCO and HCCS radicals have been determined by ab initio SCF and Møller-Plesset perturbation theory calculations using split-valence plus polarization basis sets. When optimized at a correlated level the ground state, 2A″, of HCCO is bent with a linear 2Π( 2A′) excited state forming the other half of a Renner-Teller pair. In contrast, ground state HCCS is predicted to be linear at all levels of calculation considered. The UMP3/6-31 G* predictions for the geometries of HCCO are: 2A″, r e(CH) = 1.074 Å, r e(CC) = 1.301 Å, r e(CO) = 1.170 Å, α e(CCH) = 133.23°, α e(CCO) = 169.96°; and 2Π( 2A′), r e(CH) = 1.064 Å, r e(CC) = 1.264 Å and r e(CO) = 1.181 Å. The UMP3/6-3 IG* geometry optimization for HCCS predicted: 2Π, r e(CH) = 1.066 Å, r e(CC) = 1.212 Å, and r e(CS) = 1.634 Å.