THEORETICAL-STUDIES ON POTENTIAL-ENERGY F UNCTION AND THE ISOTOPIC EFFECTS OF VIBRATIONAL-SPECTRA FOR HYPOFLUOROUS ACID

Various isotopic species of hypofluorous acid, HOF, have been a subjec t of many vibrational spectroscopic studies, The object of these detai led analyses is to obtain accurate spectroscopic data of the various i sotopic species of this molecule and to provide information about the structures and the potential energy surface. In this paper, some force constants of hypofluorous acid have been optimized from the compariso n between the experimental and the calculated vibrational energy level s, the others have been fixed to the values of the empirical farce con stants given by Halenon and Ha(J. Chem. Phys., 1988, 89: 4885). A new potential energy function is obtained by using the transformation betw een the force constants and the potential energy parameters of the MOR BID form suggested by Jensen(J. Mel. Spectrosc, 1989, 133: 468). The s pectra of the vibrational excited states of the molecules (HOF)-O-16, (HOF)-O-18, (DOF)-O-16, and (DOF)-O-18 have been calculated by using t he TRIATOM program, which uses the basis set expansion and is thus str ictly variational. In molecules (HOF)-O-18, (DOF)-O-16, (DOF)-O-18, th e vibrational frequency shifts relative to HOF specie have been calcul ated. These calculated shifts are in agreement with the experimental v alues. In addition, for the vibrational excited states of the (HOF)-O- 16, (HOF)-O-18, (DOF)-O-16 and (DOF)-O-18, some unobserved vibrational energy levels and their isotopic effects have been predicted based on the new potential energy function of the hypofluorous acid(HOF). For molecules (HOF)-O-18, (DOF)-O-16, and (DOF)-O-18, the vibrational freq uency shifts relative to HOF species hold up appromately the combinati on rule: Delta v((HOF)-O-18) + Delta v((DOF)-O-16) approximate to Delt a v((DOF)-O-18). In particular, for DOF molecule, it is shown that the stretching vibrational fundamental frequency blue shifts relative to HOF specie is -2.13 cm(-1), which is close to the experimental values( -2.10 cm(-1)). For the stretching vibrational excited states of the mo lecule DOF, the excited vibrational frequency blue shifts have been pr edicted, for example, the blue shift is -4.2 cm(-1), -5.6 cm(-1) and - 5.3 cm(-1) for the vibrational states(002), (003) and (004) of the DOF , respectively.