Honors Project On-Campus Access Only
In this work, the fundamental concepts from quantum mechanics relating to the study of diatomic molecules (molecules composed of two atoms) are developed at a level suitable for upper level chemistry or physics undergraduates who have had some previous exposure to quantum mechanics. The theory portion of this project gives a replication of a quantum treatment of molecular vibration and angular momentum, and then focuses on the small energy splittings in diatomics that are caused by the interactions of the various angular momenta in the molecules. Emphasis is also given to the theoretical origin of the famous Hund’s coupling cases, with a special focus given to Hund’s coupling case c. Selection rules for transitions are developed in the context of molecular symmetry and conservation laws, and several transition diagrams important for the molecule gold sulfide (AuS) are then discussed in detail. Later in the paper, experimental methods used by the Varberg lab at Macalester College for the generation and analysis of diatomic molecules such as AuS are explained. Spectra of the molecule at several different levels of resolution are presented and discussed. We report a vibrational spectrum of the whole visible region and a small portion of the near infrared region revealing four low lying excited electronic states, including a spin-forbidden state. Several vibrational bands were recorded at higher resolution, revealing rotational structure. Finally, smaller portions of these bands are analyzed at even higher resolution using more advanced techniques, revealing the presence of hyperfine structure, which splits each rotational line into four components, as expected for a molecule with a nuclear spin of 1/2.
Pearlman, Bradley, "High Resolution Electronic Spectroscopy of Gold Sulfide, AuS" (2016). Chemistry Honors Projects. 27.
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