Extracting picosecond time constants from steady-state spectroscopy: A physical chemistry experiment

摘要

Femtosecond spectroscopy is a key technique in modern physical chemistry research. Thus, femtosecond techniques, as well as molecular processes occurring on femto- to picosecond time scales, should be included in a physical chemistry curriculum. Usually, experiments covering the topic are challenging due to costly equipment and laser safety issues. A laboratory experiment is described that allows students to trace picosecond kinetics with safe and affordable equipment. The students record temperature-dependent IR spectra of an iron carbonyl complex, tricarbonyl(η~4-1,5-cyclooctadiene)iron. Due to "turnstile" motion of the ligands a coalescence of IR bands is observed. By simulating the spectra, the picosecond time constants of the motion and further spectroscopic parameters may be extracted. An Arrhenius analysis yields the barrier for the turnstile motion.