The equilibrium structure of propadienylidene

A coupled-cluster study of the equilibrium geometry of propadienylidene (C(3)H(2)) is presented. Deviations between a recently reported experimental r(e) structure and those computed at the CCSD(T)/cc-pVQZ and CCSD(T)/cc-pCVQZ levels are larger than expected. A closer analysis reveals that this discrepancy is due to inaccuracies in the cubic force field that was used to correct the measured rotational constants for vibrational effects. A satisfactory agreement between theory and experiment is obtained if the vibrational effects on the rotational constants are computed from harmonic and cubic force fields determined at either the CCSD(T)/cc-pVTZ and CCSD(T)/cc-pCVTZ levels. Revised values for the "experimental" r(e) structure of propadienylidene are also given. (C) 1999 Elsevier Science B.V. All rights reserved.