Instrument Development for Laser Spectroscopy of Gas-Phase Molecules

Sammanfattning

In this thesis, a laser-based spectroscopic instrument combining resonance-enhanced multiphoton ionisation (REMPI) with time-of-flight mass spectrometry (TOF-MS) is developed, optimised, and applied to the study of gas-phase molecules. The system enables the generation of cold molecular beams under high-vacuum conditions, provides tunable ultraviolet (UV) radiation for resonant excitation, and allows massresolveddetection of photoions with high sensitivity and selectivity. The performance of the REMPI–TOF setup is first tested using toluene as a benchmark molecule. TOF and mass spectra are used to verify mass calibration and resolution, while wavelength-resolved REMPI measurements demonstrate selective excitation of electronic and vibronic transitions under conditions of strong rotational and vibrational cooling, corresponding to molecular temperatures of only a few kelvin.The study is subsequently extended to the chiral aromatic alcohol (R)-1-phenylethanol. Due to its low vapour pressure at room temperature, an internally heated oven is employed to ensure stable sample introduction into the molecular beam. Mass-selected REMPI spectra recorded with different carrier gases reveal how the expansion conditions influence signal intensity, stability, and clustering behaviour. Finally, REMPI spectroscopy is applied to weakly bound molecular complexes, including toluene dimers and chiral complexes formed between (R)-1-phenylethanol and chiral alcohols. In addition, a high-vacuum source chamber was designed, constructed, and characterised at the University of Gothenburg, and subsequently integrated into an experimental setup at the University of Hamburg, where it enables flexible molecular-beam generation for future spectroscopic studies. Overall, this work demonstrates that the developed REMPI–TOF mass spectrometer provides a versatile and sensitive instrument for high-resolution, mass-resolved ectroscopy of isolated molecules and weakly bound molecular complexes in the gas phase.