CALCULATION OF VIBRATIONAL (J=0) EXCITATION-ENERGIES AND BAND INTENSITIES OF FORMALDEHYDE USING THE RECURSIVE RESIDUE GENERATION METHOD

We use the recursive residue generation method (RRGM) with an exact ki netic energy operator to calculate vibrational excitation energies and band intensities for formaldehyde. The basis is a product of one-dime nsional potential optimized discrete variable representation (PO-DVR) functions for each coordinate. We exploit the symmetry by using symmet ry adapted basis functions obtained by taking linear combinations of P O-DVR functions. Our largest basis set consists of 798 600 functions ( per symmetry block). The Lanczos tridiagonal representation of the Ham iltonian is generated iteratively (without constructing matrix element s explicitly) by sequential transformation. We determine a six-dimensi onal dipole moment function from the ab initio dipole moment values co mputed at the QCISD level with a 6-311 ++ G(d,p) basis set. We converg ed all A(1), B-2 and B-1 vibrational states up to the combination band with two quanta in the C-O stretch and one quantum in a C-H stretch a t about 6 350 cm(-1) above zero point energy. We present a simulated ( J = 0) infrared spectrum of CH2O for transitions from the ground state . (C) 1996 American Institute of Physics.