| 概 要 |
(1) 15:00-16:00
Dr. Chien-Ming Tseng 曾建銘 (IMS Fellow, Hishikawa group, IMS)
"Molecular Beam Studies on the Photodissociation Dynamics of Aromatics and Biomolecules"
Recent developments of multi-mass ion imaging on the photodissociation dynamics studies will be presented. This technique is suitable to apply on the aromatic and biomolecules which have multiple dissociation channels and slow dissociation rates. A six-membered to seven-membered ring isomerization was observed for photodissociation processes involving toluene, aniline and 4-methylpyridine, indicating a general isomerization mechanism for all such aromatic molecules. The significance is that during the isomerization, atoms (i.e., carbon, nitrogen and hydrogen)belonging to respective alkyl or amino groups are involved in an exchange with atoms within the aromatic ring. The suggestion of the deactivation from the optical bright state (π π* state) to the dark state ( repulsive πσ* state) through conical intersection has been made to explain the ultrafast decay pathway to dissipate the absorbed UV photon energy of aromatic and biomolecules. The results are the H-atom transfer on the excited state or internalconversion to the ground state. For small tyrosine chromophores, such as phenol, 4- methylphenol, and 4-ethylphenol, H-atom elimination from a repulsive excited state plays a key role. However, dissociation is quenched in large chromophores like 4-(2-aminoethyl)-phenol. Likewise, the studies of indole, 3-methyl-indole, tryptoamine and tryptophan are also the way to go deep into the photochemistry issue of amino acid gradually. The photodissociation of N-methyl-pyrrole, anisole and N-methylindole is the another illustration of the non-hydride heteroaromatic molecules with N-CH3/O-CH3 πσ* state. Furthermore, 7-azaindole, 2-aminopyridine and 8-Hydroxyquinoline were studied to clarify the repulsive N-H/O-H πσ* state which opens up a new aspect to describe the excited-state photophysics of DNA model compounds.
(2) 16:00-17:00
Dr. Masato Hayashi 林雅人 (Postdoc, Ohshima Group, IMS)
"Millimeter-wave spectroscopy of the vinyl radical"
Millimeter-wave spectroscopy combined with a pulsed-jet expansion technique was applied to detect the vinyl radical produced in the supersonic jet with the UV laser photolysis. The proton tunneling- rotation transitions, as well as the pure rotational transitions, have been observed for the H2CCH [1] and H2CCD isotopic species to determine tunneling splitting and the potential barrier height for the alpha proton (H/D) tunneling motion. Although the H2CCH and H2CCD isotopic species have very different values for the tunneling splitting, 16.185, 1.187 GHz, they have almost the same barrier heights of 1580 and 1520 cm-1. As for the HDCCH species, the pure rotational transitions (both a- and b-types) of only one isomer (cis- HDCCH) were observed in the jet, but no cis-trans tunneling transitions were detected, meaning that HDCCH has two stable cis- and trans-isomers. The zero point energy difference in the ground state between the cis- and trans-HDCCH isomers is calculated to be 38 cm-1 with the CCSD(T)/aug-cc-pVTZ level ab initio calculation to support the present result. We also observed the larger off-diagonal (delta I = ±1) hyperfine interaction for H2CCD which causes the nuclear spin conversion between the ortho (I=1) and para (I=0) H2CCD vinyl.
[1] J. Chem. Phys. 120, 3604 (2004).
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