RESUMO
Thermal CO desorption from photoexcited free metal-carbonyl clusters has been resolved in real time using two-color pump-probe photoelectron spectroscopy. Sequential energy dissipation steps between the initial photoexcitation and the final desorption event, e.g., electron relaxation and thermalization, have been resolved for Au2(CO)(-) and Pt2(CO)5-. The desorption rates for the two clusters differ considerably due to the different numbers of vibrational degrees of freedom. The unimolecular CO-desorption thresholds of Au2(CO)(-) and Pt2(CO)5- have been approximated by means of a statistical Rice-Ramsperger-Kassel calculation using the experimentally derived desorption rate constants.
RESUMO
The photoacoustic spectra of light- and dark-adapted bacteriorhodopsin in aqueous and mixed water-glyc-erol (1:2) suspensions are studied in the 90-300 K temperature range. Photochemical transients are observed and interpreted in terms of the known photocycles of trans- and 13-cis-bacteriorhodopsin. The spectra differ from those obtained by low temperature optical absorption spectroscopy of glassy glycerol-water suspensions.