CRASY: correlating rotational raman spectroscopy with mass & electron spectroscopy

Abstract

Correlated Rotational Alignment Spectroscopy (CRASY) is a powerful technique that correlates rotational spectra with ion mass detection, enabling for the detailed analysis of complex and heterogeneous molecular samples. We conducted high-resolution rotational Raman spectroscopy on furan, measuring rotational spectra for the first time, including those of the heavy isotopologues (13C and 18O) at natural abundance. This allowed us to precisely determine furan’s equilibrium structure, with results aligning closely with the semi-experimental values found in the literature. While analyzing the furan dimer spectrum, we encountered challenges hinting at multiple conformers. Nevertheless, our Pearson correlation analysis provided evidence for cluster fragmentation. The study of butadiene through CRASY marked another first in high-resolution rotational Raman spectroscopy by measuring rotational spectra for both butadiene and 13C-butadienes. The fitting of rotational constants revealed a discrepancy in previously published rotational constants, specifically a difference in the δk rotational constant. I conducted a full structural analysis, based on rotational spectra from all available literature sources. This analysis uncovered surprising variations in the CH bond lengths within the butadiene molecule. The thesis also describes the first rotational Raman spectrum measured for pyridine. A notable discovery was the identification of the protonated pyridine monomer, formed as a product of pyridine dimer or larger cluster fragmentation. I further expanded my analysis by exploring mass-correlated rotational Raman spectra, allowing us to identify and assign all fragments originating from furan, butadiene, and pyridine. Overall, this thesis illustrates the efficacy of CRASY in analyzing complex molecular systems. It excels at distinguishing sample components, assigning fragment signals to their parent molecules, and identifying sample impurities. The insights gained from our analyses of furan, butadiene, and pyridine contribute to our understanding of these molecules and highlight the potential of this innovative spectroscopic technique.