Local versus hyperspherical modes of formaldehyde

Near-degenerate local versus hyperspherical modes of H₂CO are evaluated as vibrationally highly excited H₂C-stretches coupled to cold CO-bonds, for the electronic ground state (S ₀). Similar to isolated CH₂ fragments, the wavefunctions of local modes have frontier lobes pointing towards the two equivalent H·+·HCO radical product configurations. In contrast, the wavefunctions of hyperspherical modes extend approximately along arcs on spheres around the four-atom-coincidence. The wavefunctions are represented by reduced linear combinations of symmetry-adapted products of Morse times harmonic oscillator wavefunctions (LCSPM-HO). The dominant basis functions constituting the molecular vibrational states are selected by an efficient reduction technique.