Isotopic effects in the ground state of the non-symmetrical isotopomers of CuCl2

The rovibrational structure of the ground state of the non-symmetrical isotopomers of CuCl2((ClCuCl)-Cl-35-Cu-63-Cl-37 and (ClCuCl)-Cl-35-Cu-65-Cl-37) has been investigated. Laser induced fluorescence spectra were recorded on a BOMEM DA03 Fourier transform spectrometer in the range 10000-16500 cm(-1) for nu(1)('') = 0-12 and nu(3)('') = 0-8. A non-linear least-squares cm minimization allows to obtain both rovibrational constants and isotopic factors by fitting data of one symmetrical isotopomer of CuCl2 with the corresponding non-symmetrical isotopomer having the same copper isotope. The RMS deviation is better than 0.029 cm(-1) for each case. We discuss the isotopic effects and show that breakdown of the Born-Oppenheimer approximation has to be considered.