In this project supported by the Experimental Physical Chemistry Program of the Chemistry Division, Tomas Baer will use resonance enhanced multi-photon ionization spectroscopy (REMPI) of jet-cooled molecules to investigate the ultraviolet spectra and conformational equilibria of ring and open-chain molecules such as ketones, ethers, and hydrocarbons. Temperature-dependent spectral data will yield conformational enthalpy differences which can be compared with values from calculations. Gas-phase measurements will be related to solution studies via solvent effects. Vibrational relaxation-isomerization rates in the supersonic expansion will be modeled using the master equation. The accurate measurement of interaction energies will provide valuable information about the nature and strength of non-bonded interactions of alkyl groups in organic molecules. Many molecules have flexible structures, where the overall positions of atoms can vary significantly without breaking or making any of the strong chemical bonds that connect the atoms. The many forces exerted among different regions of a molecule that are much weaker than chemical bonds can strongly influence the overall arrangement of atoms in the molecule. For large molecular systems (such as biological molecules), the collective effect of these small forces can play a dominant role in determining the structure, and thus the functional behavior, of the molecule. These studies will explore the nature of some of these weak interaction energies. Results from this project could help to refine the data bases used for computational predictions of properties of large organic molecules.
