AB-INITIO CALIBRATION STUDY OF THE HEAT OF FORMATION, GEOMETRY, AND ANHARMONIC-FORCE FIELD OF FLUOROACETYLENE

The heat of formation, geometry, harmonic frequencies, and quartic for ce field of the fluoroacetylene (FCCH) molecule have been computed usi ng coupled cluster methods and large basis sets. Inner-shell correlati on was included explicitly, as were both cubic and quartic resonances, Our final force field, which does not involve any empirical adjustmen t, reproduces 36 vibrational band origins with a mean absolute error o f 1.6 cm(-1). The bending anharmonicities exhibit a marked basis set s ensitivity, due almost entirely to the CCF bend. Evidence was found fo r the existence of an additional quartic resonance, v(2) approximate t o v(3) 2v(4). OUT best estimates, with conservative uncertainties, for the heat of formation and the geometry are 25.3 +/- 0.3 kcal/mol and r(e)(CF) = 1.2768 +/- 0.0005, r(e)(CC) = 1.1964 +/- 0.0005, and r(e)(C H) = 1.0601 +/- 0.0005 Angstrom.