Equilibrium structure and spectroscopic constants of difluorovinylidene: An ab initio study

Highly correlated ab initio calculations with large basis sets are reported for difluorovinylidene, F2CC. Based on CCSD(T)/aug-cc-pVQZ results and tak ing core correlation effects properly into account, a reliable theoretical equilibrium geometry is derived: r(e)(CC) = 134.74(10) pm, r(e)(CF) = 131.0 0(10) pm, and angle (e)(FCC) = 123.23(10)degrees. The error bars are estima ted from analogous comparative calculations on the equilibrium structures o f the CF2, C-2, and C-3 species. Correlated harmonic [CCSD(T)/aug-cc-pVQZ] and anharmonic [CCSD(T)/TZ2Pf] force fields provide theoretical values for the fundamental vibrational wavenumbers which are in excellent agreement wi th those measured previously in an argon matrix. Many spectroscopic constan ts of F2CC are predicted. In addition, the energy of F2CC relative to diflu oroethyne (FCCF) and the barrier to isomerization from F2CC to FCCF have be en reinvestigated by means of the present high-level ab initio calculations . (C) 2001 Academic Press.