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Chemistry and Physics


College of Arts and Sciences

Faculty Mentor #1

Giancarlo, Leanna


The bond length along which two atoms vibrate can be altered in order to construct a potential energy surface used to determine the bond dissociation energy of a diatomic molecule. Carbon monoxide was initially used as the diatomic molecule of choice in this ChemCompute lab experiment. The bond length of carbon monoxide was altered in the range of .086 to .177 nm, and the electronic energy produced was recorded. A potential energy curve was constructed at these bond lengths until the molecule dissociated; a relative potential energy curve was then constructed. The equilibrium bond length, 0.113 nm, and the well depth (De”) were found, 692.539 kJ/mol. Using the force constant of 1902 N/m for carbon monoxide, the vibrational frequency (ve) was found to be 2169 cm-1 . The zero-point energy, which is the difference between the bottom of the well and the lowest possible vibrational level, was determined to be 1084 cm-1. The bond dissociation energy (Do”) for carbon monoxide was then found to be 669.6 kJ/mol with a 37.5% error. Using another set of molecules, sulfur monoxide (SO) and hydrochloric acid (HCl), equilibrium bond lengths of 0.135 and 0.128 nm, vibrational frequencies of 1685 and 3147 cm-1, and zero-point energies of 842.7 and 1574 cm-1 were found, respectively. To assess the accuracy of the calculations from ChemCompute further, the bond dissociation energy was also found for SO and HCl with a value of 242.9 kJ/mol and 53.4% error for SO and 24.60 kJ/mol with 94.5% error for HCl. As the number of bonds decreases between a diatomic molecule, the accuracy of the bond dissociation energy decreases. While being a useful tool in visualizing bond length and the potential energy surface for a diatomic molecule, due to these computational methods relying on experimentally determined values and the Gaussian basis set, the data produced is sometimes inaccurate in the determination of dissociation energies.

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