Application of broadband Fourier transform microwave techniques to dynamic rotational spectroscopy.

摘要

Rotational spectroscopy has long been a valuable tool used to understand molecular structure at low energies. Because the rotational spectrum is linked to the moments of inertia of a molecule, and the moments of inertia are linked to the geometry of a molecule, rotational spectroscopy is able to uncover precise structures of polar molecules in the gas phase. Our laboratory has developed the field of dynamic rotational spectroscopy (DRS) where the rotational spectra of vibrationally excited molecules are measured and analyzed to uncover dynamic information. In the presence of intramolecular vibrational energy redistribution (IVR), the moments of inertia of a molecule are no longer static properties, but become time-dependent properties. When vibrational motion causes the geometry of a molecule to change on the timescale of molecular rotation, dynamic information can be accessed through the rotational spectrum.;We have developed a chirped-pulse Fourier transform microwave (CP-FTMW) spectrometer capable of measuring a broadband 11 GHz rotational spectrum using a single valve pulse and a single microwave polarizing pulse. This spectrometer is ideally suited to measure the dynamic rotational spectra of excited state molecules. It measures the molecular rotational spectrum much more quickly than the previous narrow band FTMW spectrometer, and it measures the relative intensities accurately, which is important for the overall lineshape analysis in DRS. This thesis will briefly describe the design and operation of the CP-FTMW spectrometer. It will also present the dynamic rotational spectroscopy of phenylacetylene, cyclopropane carboxaldehyde, and 4-fluorobut-1-yne.