The Experimental Physical Chemistry Program will support Charles S. Parmenter of Indiana University in Bloomington to continue his studies of state-resolved energy transfer in various molecules. The gist of his experiment is to use a supersonic molecular beam technique to generate molecules in a few, very specific rotational states. Laser pumping is then used to excite the molecule to the first singlet electronic excited state, and dispersed fluorescence detection of states populated by inelastic scattering yields relative cross sections for single collision energy transfer channels. Past efforts involved scattering of glyoxal (12 vibrational modes) from rare gases or diatomic molecules. During this funding period, the investigator will extend his studies on glyoxal to collisions with helium or diatomic hydrogen. He will also study relative cross sections as a function of center-of-mass energy between collision partners. Finally, the crossed beam experiments will be extended to deuterated formaldehyde, a molecular system far different from glyoxal due to its nonplanar excited electronic state, presence of a dipole moment and extreme anharmonicity in an active vibrational mode. The research is directed at the problem of vibrational and rotational energy flow within polyatomic molecules. This is central to the problem of how molecules acquire the activation energy needed for reactions. The collision-free vibrational energy flow is a fundamental aspect of dissociation or isomerization of molecules with high vibrational excitation.
