Computed bond energies and vibrational frequencies for ClHCl, BrHBr, and IHI, including isotope effects and anharmonicity

The bond-energy-bond-order (BEBO) method of Johnston and Parr predicts ClHCl, BrHBr, and IHI are all bound and symmetric. When corrected for anharmonicity of the asymmetric stretch normal mode, it predicts the following vibrational frequencies in cm^-1 (experimental results are in parentheses; s is the symmetric stretch and a is the asymmetric stretch) : ClHCl, s: 371 (259) ; ClDCl, s: 370 (265), a: 318 (463); BrHBr, s: 222 (165), a: 533 (727); BrDBr, s: 222 (170), 442 (496); IHI, s: 165 (121), a: 862 (686); IDI, s: 165 (124), a: 677 (470). The predictions of the London-Eyring-Polanyi- Sato (LEPS) method for vibration frequencies are presented but are in much worse agreement with experiment. The BEBO method predicts the following depths of the potential energy minima (in kcal/mole) and equilibrium bond distances (in 10^-8 cm), respectively: ClHCl, 1.56, 1.45; BrHBr, 3.02, 1.60; IHI, 6.77, 1.79.