Soo‐Chang Yu

Ultrafast transient Raman investigation of geminate recombination and vibrational energy relaxation in iodine: The role of energy relaxation pathways to solvent vibrations

Direct observation of geminate recombination and vibrational energy relaxation in the X state of iodine has been accomplished using picosecond Raman spectroscopy. The dynamics of energy relaxation from vibrational levels ranging from v=52 to v=1 have been observed. These levels correspond to absolute energies of 9300 to 210 cm−1 above the zero point in the X potential. The effect of relaxation to solvent vibrations in resonance with I2 vibrations has been studied. The efficiency of these vibrational–vibrational relaxation channels is found to be very solvent dependent. The results suggest that the vibrational coupling between the excited iodine oscillator and the solvent is drastically affected by the nature of the normal mode character of the solvent vibration.

Ultrafast investigation of condensed phase chemical reaction dynamics using transient vibrational spectroscopy: Geminate recombination, vibrational energy relaxation, and electronic decay of the iodine A’ excited state

The reaction dynamics of iodine geminate recombination on the excited A’ 3Π2u state are investigated using picosecond transient Raman spectroscopy. Vibrational energy relaxation and the dynamics of geminate recombination are directly observed in the transient Raman spectrum. Geminate recombination rates are significantly slower for the excited electronic state compared to the ground electronic state. This observation implies that a fundamentally different geminate recombination mechanism is responsible for the formation of the A’ 3Π2u state. Evidence is reported which suggests the possible role of iodine atom–solvent complexes in the reaction step leading from photodissociated atoms to formation of the excited state. The solvent dependence of vibrational energy relaxation suggests that the rate is dominated by V–T (and possibly V–R) energy relaxation which is also found to be significantly slower in the excited electronic state compared to the ground state. In n‐hexane the vibrational relaxation rate appe...

Picosecond Raman investigations of interligand electron transfer in transition metal complexes

Two color picosecond Raman spectroscopy has been utilized to measure interligand electron transfer in the excited MLCT states of mixed ligand Ru(II) complexes. No contribution to electron transfer was found from hot vibrational levels produced by photoexcitation. For thermally relaxed vibrational levels the first direct measurement of the upper limit to the rate of interligand electron hopping is reported. It was found that the rate from the thermally equilibrated vibrational states was ≤2×106 s−1. Low temperature Raman spectra indicate that the slow rate of electron transfer creates a nonstatistical energy distribution between dissimilar ligands. The implications of these results are discussed within the framework of electron transfer theory.

Direct measurement of solvent cage dynamics following photodissociation of iodine using picosecond Raman spectroscopy

Photodissociation of iodine in CCl4 at 532 nm deposits 6300 cm−1 of energy into the solvent cage immediately surrounding the solute. Picosecond Raman spectroscopy has been used to investigate the dissipation of this energy in the solvent coordinate by monitoring time‐dependent shifts in the Raman lineshapes of the local solvent cage.

Direct measurement of photodissociation, geminate recombination, and vibrational cooling in iodine using picosecond Raman spectroscopy

The photodissociation and geminate recombination of iodine in cyclohexane has been studied by directly monitoring the vibrational coordinates using transient Raman spectroscopy. Energy relaxation as a function of vibrational energy gap has been measured for vibrational spacings of 210 to 130 cm−1. These vibrational levels correspond approximately to v=3 to v=52 with energies 740 to 9300 cm−1 above the zero point level. The results support earlier experiments in that over 100 ps is required to completely relax the vibrational energy.

Direct measurement of vibrational energy relaxation in photoexcited deoxyhemoglobin using picosecond Raman spectroscopy

We have directly observed hot vibrations in photoexcited deoxyhemoglobin. The data quantitatively indicate a heme vibrational temperature of 20 K above room temperature within the time sampled by an 8ps laser pulse. The slow component of vibrational relaxation occurs with a rate constant of (2.5ps)1. Similar dynamics are observed in oxyhemoglobin. The initial stages of recombmation of 02 with the heme following photodissociation of oxyhemoglobin are observed in the transient vibrational spectrum. Contrary to previous work, we do not observe the influence of protein dynamics on 02 recombination.

The Observation of Vibrational Relaxation and Solvent Reorientation Following Ultrafast Photodissociation of Cr(CO)6

The photodissociation of Cr(CO)6 at 266nm has been studied in cyclohexane and n-propanol by using picosecond Raman spectroscopy. Vibrational relaxation on a time scale of 100ps has been observed in cyclohexane in both the Stokes and anti-Stokes spectra. Raman band shifts have been observed in n-propanol within 100ps which are assigned to solvent coordination and reorientation from the alkane coordinated intermediate to the more stable oxygen-metal coordinated complex.