Infrared spectroscopy of cold molecules

A long path collisional cooling cell has been installed at the Far-Infrared beamline at the Australian Synchrotron to study the infrared spectrum of molecules at cryogenic temperatures. New transfer optics and vacuum chambers were designed in order to allow study in the far infrared region where the synchrotron source provides the most advantage. Experiments using this cooling cell can be divided into two themes: rotationally resolved high resolution spectroscopy and low resolution spectroscopy of aerosols (solid or liquid particles suspended in a gas). Chapter 1 contains the background information and theory important to high resolution spectroscopy. This chapter also contains details of the instrumentation used and the modifications to the optics of the cooling cell. Chapter 2.1 is the first publication, a report on the performance of the Far-IR beamline and the optical modifications to the cooling cell. This paper also contains examples of the data obtained with the new arrangement. The far-IR spectrum of carbon dioxide aerosols and the high resolution spectrum of 1,1-difluoroethane recorded at room temperature and at 154 K, showing the advantages of cooling for high resolution FTIR spectroscopy. Prior to the completion of the optical modifications the mid-IR spectrum of carbon-13 enriched C2F4 was measured in the cooling cell at 150 K. Chapter 2.2 contains the structural, vibrational and rovibrational analysis of this molecule. The ground state rotational constants for 12C13CF4 and 13C2F4 were determined and used to compute a semi-experimental equilibrium geometry. Upper state rotational constants were also determined. Chapter 2.3 contains a publication where the pure rotational spectrum of the important interstellar molecule oxirane (cyclic-C2H4O) was measured between 15 and 73 cm-1 (0.4-2.2 THz).