Microwave and Terahertz Investigations of Radical Diatomic Molecules: New Avenues for Rotational Spectroscopy

Abstract

The pure rotational spectra of several molecules have been measured in the Ziurys laboratory across the novel range 200-1100 GHz via direct absorption methods. Involved in the measurements have been several instrumental upgrades in the Ziurys Group. One result of this work is the first measurement of CrBr in its electronic ground state, X6Σ+. This study contributes new insight into the theory of angular momentum coupling in high-spin electronic states, expansion of periodic trends for 3d-metal bromides, and the addition of previously undetermined spectroscopic constants, including equilibrium parameters. This thesis also includes an example of the rare measurement of MgCl in excited 2Σ+ states not normally accessible using pure rotational spectroscopic methods, as well as the first high-resolution direct measurement of the metal hydride FeH in its X4∆i state, which is the first measurement beyond 1 THz conducted in the Ziurys Group.These projects were carried out on three separate direct absorption spectrometers in the Ziurys group, and utilized several difficult means of synthesis, such as metal vapor production via Broida ovens or separation from organometallic precursors aided by applied electrical discharges. In addition, one spectrometer system was upgraded to operate up to and beyond 1.4 THz, including new software and chain multipliers which may be conveniently swapped into the experimental setup. Transitions recorded for FeH in this thesis will allow astronomers to confidently detect this highly sought-after molecule in interstellar space. The measured spectra were analyzed using several effective case (a) or case (b) Hamiltonians comprised of rotational and fine structure terms, often containing hyperfine terms, with spectroscopic parameters being determined from each. Equilibrium parameters were determined from the CrBr and excited state MgCl projects, providing comparison parameters for future investigation. These projects served as good tests for the existing theory of angular momentum coupling, particularly in higher order effects such as the fourth-order correction to the spin-orbit interaction, where only limited empirical testing has thus far been conducted. This work also contributes to further testing of the accuracy of ab-initio methods and the theory of the formation of electronic states within a molecule.