Physical Chemistry • Spectroscopy • Solid State • Biophysical • Theoretical Vibrational spectroscopy, together with laser excitation and temperature jump, elucidates the dynamics of molecules in condensed phases
Vibrational and related spectroscopies are remarkably sensitive to details of molecular motion and conformation. Laser "hole-burning" and temperature jump experiments lead to kinetic information on systems ranging from H2 moving in ice to the segregation of components in a model lipid bilayer.
Spectral hole-burning of the N-D stretching band of NH3D+ is used to rotate the ions into nonequilibrium positions and is followed by monitoring the infrared spectrum. After the hole-burning, the molecules relax to their original positions, often by tunneling. The Strauss group uses the changing spectra to assign vibrational bands and determine the kinetics. Simple salts such as ammonium show discrete vibrational bands, while disordered salts such as (NH4)xKy(SO4)2 show broad vibrational bands. Hole-burning results in narrow holes and these can be used to resolve the spectrum in the disordered sulfates and in the even more disordered amorphous polymers. The N-D bands of amino acid salts similarly doped with deuterium can also be burned. The hole-burning is used to determine the environment of the amine group in both the amino acids and in small polypeptides.
Alkane-chain systems from alkanes themselves to lipid bilayers show numerous phase changes with temperature. These phase changes are accompanied by conformational changes, which can be determined by infrared and Raman spectroscopies. Systems of mixed chain length segregate, and this too shows up in the spectra. The rate of segregation varies with chain length differences and with temperature. The Strauss group finds that even phosphatidyl cholines segregate into micro regions of different composition. Hole-burning of bands such as C-D stretches provide kinetics of the interior motions of the chains.
The hydrogen molecule, H2, is a unique probe of intermolecular interactions. The Strauss group uses Raman and neutron spectroscopies to show that hydrogen rotates and translates remarkably unhindered in both water and ice, but that hydrogen is considerably more hindered in the channels of zeolites. The spectra are interpreted in terms of time-dependent interactions between the hydrogen and the water molecules.
Professor, A.B. (1957), M.A. (1958), Ph.D. (1960), Columbia University; Postdoctoral Fellow, Oxford (1960-61); Visiting appointments at Indian Institute of Technology (1968-69); Fudan University, Shanghai (1982); University of Tokyo (1982); University of Paris (1986); Editor, Annual Review of Physical Chemistry (1985-2000); Associate Dean (Undergraduate Affairs), College of Chemistry 1995- 2008; Bomem-Michelson Prize for Spectroscopy (1994); Lippincott Award for Vibrational Spectroscopy (1994). The Berkeley Citation, 2003; Berkeley Academic Senate, Berkeley Faculty Service Award, 2008