Experimental and theoretical investigations of highly-excited molecules are presented that advance the current state of knowledge of intramolecular interactions in highly-excited molecular states.

A quantitative analysis of intramolecular interactions in excited hydrogen fluoride is presented, in which the rotational levels of the B ¹Σ⁺, v = 29 vibronic level are shown to mix with the corresponding e-parity components of the C ¹Π, v = 0 level. Extrapolating the experimentally-derived mixing parameter to the unperturbed limit reveals an unperturbed value of the a_F hyperfine parameter of 4132(25) MHz.

Coupling energies between the ion-pair curve and long-range asymptotes of covalent states are calculated for a large number of alkali–alkali collision channels, revealing the dependence on the internuclear distance at which the crossing takes place and forming a foundational step for the calculation of cross-sections and rate coefficients for different charge-exchange and other processes.

To advance the experimental investigation of these systems, optical instrumentation and associated control systems have been designed and constructed for cooling and trapping lithium in preparation for experimental studies of cold-collisions that will be informed by, and ultimately a test of, some of these calculated ionic–covalent coupling energies. A novel scheme for systematic optimization of peak-locking has been developed and implemented, providing a rigorous assessment of the optimal experimental parameters. A side-of-filter offset-locking scheme was implemented, characterizing and correcting for a previously unexplained offset in the error-signal.