| This thesis is a summary of my achievements in the study of three different types of molecular systems using Fourier Transform Microwave (FTMW) spectroscopy and ab initio computational methods in Novick's laboratory of the Southern New England Microwave Consortium. The three different types of molecular systems include: molecules with multiple tops undergoing hindered internal rotation, highly unsaturated carbon chain molecules, and unstable free radicals. For ease of understanding, this thesis is divided into four sections.;Section I is a brief introduction to rotational spectroscopy, including chapters 1 and 2. Chapter 1 explores the electronic and nuclear motions in a molecule, particularly, the internal nuclear motions including rotation and vibration, which can be studied by high resolution spectroscopy. Chapter 2 introduces fine and hyperfine structures of the rotational spectrum which are due to electronic spin-molecular overall rotation interaction, ( S•N), nuclear quadrupole coupling interaction, (I•I ), nuclear magnetic dipole-molecular overall rotation interaction, (I•N), and electronic spin-nuclear spin interaction, ( I•S).;Section II, which includes chapters 3 and 4, involves the microwave spectroscopy of molecules with multiple tops undergoing hindered internal rotation. Chapter 3, with the title "Rotational Spectra of Argon Acetone: A Two-Top internally Rotating Complex", is a draft form of a paper which appeared in the Journal of Molecular Spectroscopy 213, 122--129, (2002). The rotational constants, centrifugal distortion constants, and torsional constants, as well as molecular structure were reported. Chapter 4 is a manuscript in preparation for rotational spectroscopy of molecules with three-tops undergoing hindered internal rotation. These molecules are: Trimethylsilane, (CH3)3SiH, Trimethylsilylethyne, (CH3)3SiCCH, and Trimethylsilylbutadiyne, (CH3 )3SiCCCCH, as well as some of their silicon isotopic species. A clearly distinguished, fully resolved spectrum with three-top torsional hyperfine splittings is presented in chapter 4.;Section III, which includes chapters 5 and 6, is about the spectroscopic and quantum computational studies of highly unsaturated transient molecules.;Section IV is about the microwave spectroscopy and computational studies of unstable free radicals (open shell systems) and includes chapters 7 and 8. (Abstract shortened by UMI.). |
