JOSEPH W. NIBLER
B.S. Oregon State University, 1963
PhD. University of California, Berkeley, 1966
Dr. Nibler's research involves the use of various spectroscopic methods in the study of structures and dynamic properties of simple reactive molecules, radicals, ions, and weak complexes formed in cold molecular beams. Examples include CH3, N2H2, (CO2)2, C4N2,and high temperature molecules such as MgF2, AlO, etc. Laser photolysis and other methods are used in generating such species, and pulsed laser techniques are employed to probe their properties on a short time scale.
Part of the research involves efforts to improve new nonlinear optical techniques (such as CARS-Coherent Anti-Stokes Raman Spectroscopy and high-resolution stimulated Raman spectroscopy) for service as probing methods with high analytical sensitivity. Recent work uses a double resonance approach in which molecules are selectively pumped to upper vibrational levels via stimulated Raman excitation, followed by u.v. laser photo-ionization. This method offers sensitivity improvements of about 1000 and also permits time-of-flight mass spectral sorting of molecules in complex mixtures. From the high resolution vibrational-rotational spectra, one obtains structural parameters and detailed kinetic information about concentration changes with time.
Other research involves the study of the growth and properties of small molecular clusters formed in cold free jet expansions. The objective is to learn more about the ways in which small nucleation centers form and grow under super-saturated conditions. Coherent Raman vibrational spectra of the clusters allow one to measure local temperatures and phase properties of nm scale aggregates and to measure freezing rates as small liquid clusters convert to crystalline form during the jet expansion. In some cases, molecules on the surface can be distinguished from those in the interior of the cluster. Experimental measurement of the properties of such small clusters is of considerable interest for comparison with theoretical models and is of practical interest in designing new nano-scale materials.
Last Updated by Richard Nafshun on Tuesday, September 10, 2002