Ab initio anharmonic force field and ab initio and experimental equilibrium structures of formyl chloride

The quadratic, cubic, and semi-diagonal quartic force field of O=CHCl has been calculated at the MP2 level of theory employing a basis set of triple-zeta quality. The spectroscopic constants derived from the force field are in excellent agreement with the experimental ones. The equilibrium structure has been derived from experimental ground state rotational constants and ab initio rovibrational interaction parameters. This semi-experimental structure is in excellent agreement with the ab initio structure calculated at the CCSD(T) level of theory using a basis set of quintuple-zeta quality and a core correlation correction. The experimental mass-dependent r(m) structures are also determined and their accuracy is discussed. The recommended equilibrium geometry is: r(c)(C=O) : 1.182(1) Angstrom; r(e)(C-H) = 1.092(1) Angstrom; r(e)(C-Cl) = 1.762(1) Angstrom; angle(e)(OCH) = 126.3(1)degrees; and angle(e)(OCCl) = 123.3(1)degrees. (C) 2003 Elsevier B.V. All rights reserved.