Microwave and high resolution infrared spectra of vinyl chloride, ab initio anharmonic force field and equilibrium structure

The quadratic, cubic, and semi-diagonal quartic force field of vinyl chloride has been calculated at the MP2 level of theory employing a basis set of triple-ζ quality. The spectroscopic constants derived from this force field are compared with the experimental values. To make this comparison more complete, the rotational constants of the lowest excited state, v9 = 1 at 395 cm−1 have been determined by microwave spectroscopy and the ν12 band (around 618 cm−1) has been investigated by high-resolution infrared Fourier transform spectroscopy. 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-ζ quality and a core correlation correction. The experimental mass-dependent rm structures are also determined and their accuracy is discussed. The recommended equilibrium geometry is: r (CC) = 1.3262(10), r (CCl) = 1.7263(10), r (CHg) = 1.0784(10), r (CHc) = 1.0795(10), r (CHt) = 1.0797(10), ∠(CCCl) = 122.77(10)°, ∠(CCHg) = 123.86(10)°, ∠(CCHc) = 121.80(10)°, ∠(CCHt) = 119.29(10)°.