thesis
Development of a sensitive mid-infrared spectrometer for the study of cooled molecular ions
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Abstract
The study of molecular ions is relevant to many areas of scientific interest.
Mid-infrared laser spectroscopy functions as a useful tool for understanding
the role of molecular ions in these areas. To this end, a broadly tunable
mid-infrared difference frequency generation noise-immune cavity-enhanced
optical heterodyne molecular spectroscopy (NICE-OHMS) system has been
developed and characterized through rovibrational spectroscopy of methane.
In addition, an attempt was made to use this spectrometer to probe molecular
ions focused into an ion beam. Challenges inherent to laboratory molecular
ion spectroscopy, such as quantum dilution at high internal temperatures and
low ion number density, have been addressed through the development of an
instrument that produces rotationally cooled molecular ions coupled to the
highly sensitive spectroscopic technique NICE-OHMS. The instrument was
first explored as an extension of an ion beam spectrometer by the integration of a continuous supersonic expansion discharge source for the production
of the cooled molecular ions. Issues with the implementation led to the re-
design of the instrument for spectroscopically probing a supersonic expansion
discharge directly with NICE-OHMS. After implementing discharge modulation of the supersonic expansion source, spectra of rotationally cooled H3+ and HN2+ were acquired. This instrumental development and preliminary
spectroscopy has paved the way for a new method for the sensitive spectroscopic study of cooled molecular ions that will aid further insight into these
chemical species in many fields