Ab initio potential energy surface for vibrational state calculations of H2CO

A highly accurate potential energy function for H2CO has been developed at the CCSD(T)/cc-pVTZ level. The potential energy function is generated by the modified Shepard interpolation of the local fourth-order Taylor expansions defined at three reference points, i.e., the equilibrium structure plus two symmetrically equivalent structures located in the strongly coupled region of CH symmetric (Q(1)) and antisymmetric (Q(5)) stretching vibrational coordinates. The vibrational self-consistent field and the following vibrational configuration interaction methods have been applied to determine the fundamentals, overtones, and combination bands of H2CO. It is shown that our proposed potential energy function and a conventional quartic force field provide the different result related to the assignment of the 1(1)5(1) and 1(1)3(1)6(1) bands. The calculated vibrational energies are in good agreement with the corresponding experimental values, showing the mean absolute deviation of 7.7 cm(-1). (C) 2003 American Institute of Physics.