High Resolution Millimeter-Wave Spectroscopy of Metal Hydrosulfides and Imides

Abstract

The aim of rotational spectroscopy is to investigate the structure and the bonding character in molecules. Using millimeter-submillimeter experimental techniques, molecules are typically investigated in the ground electronic state. Therefore, one of the advantages of employing rotational spectroscopy is to determine the ground electronic state of the species under investigation. There are three different classes of molecules that are presented in this thesis: diatomic species (BaS), linear triatomic species (BaNH) and asymmetric tops LiSH, BaSH, CuSH and AlSH, including their isotopomers. Although the initial data for the BaS has been published, new rotational transitions are included in the initial data set to optimize the rotational constants for this species and its six isotopomers. The BaNH molecule is the first alkaline earth imide investigated in the gas phase. The spectroscopic data of the main isotope and its lesser isotopomers indicate a linear structure. DFT calculations suggest that the linear structure is a result of the pi bond between barium and nitrogen. The metal hydrosulfides studied here are asymmetric tops. LiSH, BaSH, CuSH and AlSH were found to be bent with an angle oscillating around 90 deg.. Since the bond angle of 90 deg. is close to that of H2S, it is believed that the sulfur p orbitals bond to metal and hydrogen. The hydroxide counterparts of the hydrosulfides that have been studied experimentally are either linear or quasilinear. The one exception thus far is CuOH, which is bent with an angle of 110 deg.. The hydrosulfide species are believed to have covalent bonding, in contrast to the metal hydroxides, which primarily have ionic bond character. The only investigated radical is the asymmetric top molecule, BaSH. The additional spin rotational terms along three molecular axes epsilon(aa), epsilon(bb), epsilon(cc) give insight into the non-spherical distribution of the one unpaired electron of the metal atom in its ground state. The non-spherical distribution has been explained by the presence of p(pi) character, which was mixed into the ground state from the nearby excited electronic states: A' and A''.