THE VIBRATIONAL-SPECTRA OF KRYPTON AND XENON DIFLUORIDE - HIGH-RESOLUTION INFRARED STUDIES AND AB-INITIO CALCULATIONS

Fourier transform infrared spectra of KrF2, XeF2, and monoisotopic (Xe F2)-Xe-136 have been recorded in the nu(3), and nu(1)+nu(3) ranges wit h an effective resolution of 0.003-0.007 cm(-1). About 10 000 rovibrat ional lines belonging to cold bands and to hot bands with nu(1), nu(2) , 2 nu(2), and nu(3) as lower levels have been assigned and fitted. Th e high-resolution results from this work and from two previous studies provide a rather complete set of precise spectroscopic constants and accurate ground-state and equilibrium geometries for both molecules. I n the case of (KrF2)-Kr-84, r(0)=188.2821(9) pm supersedes previous in correct r(0) values, and r(e)=187.6930(23) pm represents the first det ermination of the Kr-F equilibrium distance. Ab initio calculations em ploying effective core potentials and polarized double-zeta basis sets have been carried out at the following levels: self-consistent-field (SCF) theory, the Moller-Plesset second order perturbation theory (MP2 ), and coupled cluster theory with single and double excitations (CCSD ) and a perturbational treatment of triple excitations (CCSD(T)). Pron ounced correlation effects are found, especially for KrF2. The agreeme nt between the correlated theoretical and the experimental results is generally quite good. A theoretical analysis clarifies the origin of t he positive alpha(2) vibration-rotation coupling constants which have been observed for the bending vibrations in both molecules. Reliable h armonic and anharmonic force fields are presented for KrF2 and XeF2.