Extension of a regularizing algorithm for the determination of equilibriumgeometry and force field of free molecules from joint use of electron diffraction, molecular spectroscopy and ab initio data on systems with large-amplitude oscillatory motion

The previously developed integrated algorithm for the joint treatment of ga s-phase electron diffraction and vibrational spectroscopic data is extended to include systems with large-amplitude oscillatory motion. In addition, t he treatment is augmented by the inclusion of microwave rotational constant s. As in the previous work, the analysis of data from experimental sources is guided by quantum mechanical molecular geometry and force field optimiza tion results. The computed force field matrix can be corrected empirically with the aid of suitable scale factors. Centrifugal distortion corrections to interatomic distances are included. The standard deviations of the param eters determined and the correlation coefficients can now be estimated. The principal design of the developed computer program is outlined, and some m ethodological problems associated with diffraction analysis of molecules wi th large-amplitude motion are discussed. To provide an example of a problem susceptible to attack by the present method an account is made of the re-a nalysis of diffraction data for 4-fluorobenzaldehyde collected earlier on t he Balzers apparatus in Oslo. (C) 1999 Elsevier Science B.V. All rights res erved.