Date of Award
Doctor of Philosophy (PhD)
John B. Hopkins
A femtosecond time-resolved Raman spectrometer is developed to study the ultrafast dynamics of hemoprotein. The laser system consists of a dye laser synchronously pumped by the SHG of compressed ML Nd:YAG laser pulse, and a Ti:sapphire regenerative amplifier using chirped-pulse-amplification technique. The laser system provides 350 fs pulses output with 0.4 mJ/pulse energy at the repetition rate of 1 kHz. The tunability covers the whole Ti:sapphire lasing range with the use of different laser dye. Femtosecond time-resolved resonance Raman experiment shows that the ligand photodissociation quantum yield depends on the nature of ligand. With three ligands studied, CO has about 100% quantum yield while O$\sb2$ has about 40% and NO has about 20%. No significant amount of geminate recombination observed in less than 10 ps for CO and O$\sb2$. However, most of the photodissociated NO ligand geminate recombines within 30 ps. The electronic relaxation of photoexcited hemoprotein occurs in about 300 fs. While the ligand dissociated hemes are relatively vibrationally cool, the ligand bound hemes subsequent to electronic relaxation are vibrationally hot. The energy is deposited in high vibrational frequency modes with a 2 ps IVR process. The EVR process occurs in about 4-5 ps. These results are in agreement with other ultrafast hemoprotein experimental observations.
Chen, Junbo, "Development of a Femtosecond Time-Resolved Raman Spectrometer for Hemoglobin Studies." (1995). LSU Historical Dissertations and Theses. 5937.