ISOTOPIC DEPENDENCE OF BORN-OPPENHEIMER BREAKDOWN EFFECTS IN DIATOMIC HYDRIDES - THE X1-SIGMA+ STATES OF HI DI AND HBR DBR

Line positions available from literature data for HI DI and HBr DBr have been employed to determine corrections to the Born-Oppenheimer approximation. For the ground X1Σ+ states of HI and DI, an analytical effective nonadiabatic Hamiltonian with 13 fitted parameters describes experimental observables within the precision of the measurements. The analytical operator for the X1Σ+ states of HBr and DBr is defined by 12 fitted parameters and achieves similar success. Rotational and centrifugal distortion constants are determined a posteriori through perturbation theory; along with the rotationless eigenvalues, they represent the spectroscopic line positions to within the precision of the measurements. Quantum-mechanical molecular constants are also calculated for TI, T79Br, and T81Br. A detailed study of the isotopic variation of Re values in hydrogen halide ground states is made using the existing theory. © 1991.