Spectroscopy of Molecules and Molecular Complexes Inside Helium Nanodroplets

The contents of this thesis is concentrated on probing molecules and molecular clusters in helium nanodroplets (HeDs) via infrared depletion laser spectroscopy. Absorption of the incident IR radiation by molecules and molecular clusters inside HeDs results in evaporative loss of helium atoms from the droplet. This loss reduces the ionization cross-section of the droplet and causes a depletion in the ion signal, which is reflected in the mass spectra. This mass selectivity was used to aid with the assignment of individual IR bands to specific sizes of molecular clusters. This method was taken to record IR spectra of CsI(CH3OH)n for n = 1-3. The collected data in conjunction with computational calculations provides evidence for n = 1-3 the formation of the global minimum geometry possessing an increasing number of ionic hydrogen bonds as the cluster size increases. These hydrogen bonds are between the hydroxyl group and the iodine atom, with the CsI salt existing in the contact ion-pair state for all cluster sizes. In addition, the IR depletion spectra of propargyl alcohol clusters in HeDs has been presented. It was discovered that the spectra of propargyl alcohol dimers in HeDs confirms a previously unseen, high energy -C≡C-H---O hydrogen bond interaction between the two monomer units. This finding is completely different from previous gas phase studies that observed a cyclic structure that possessed O-H---O and O-H---π bond contacts. Finally, the first study of propargylamine clusters is reported. Similar to the propargyl alcohol data, the conformers assigned as the spectral carrier of the dimer and trimer spectra collected in HeDs was deemed to possess -C≡C-H---N interactions. Dimers with this binding motif are generally higher in energy and differ from the predicted global minimum, which is cyclic in nature.