1999
- INTERNATIONAL MEETING
・XIXth International Conference on Photochemisty (ORAL PRESENTATION)
- "SINGLE AND MULTI-PHOTON REACTIONS OF
HOT MOLECULES"
- Tomoyuki YATSUHASHI, Nobuaki NAKASHMA
- (Duke Univ. NC USA, Aug01-06)
- Hot molecule, which is in a highly vibrationally
excited state, plays an important role in VUV-UV photochemistry.
Hot molecules have a very high equivalent vibrational temperature
of around 2000-4000K, and a narrow initial energy distribution
which are suitable for examining the dynamics of high temperature
chemistry. We have investigated several photochemical reactions
of hot molecules in the gas phase with VUV lasers. Some examples
of hot molecule reactions will be presented with respect to single
and multi-photon reactions. 1) Benzyne has been known as a very
important intermediate in organic synthesis processes. VUV laser
irradiation of phthalic anhydride resulted in the formation of
benzyne via hot phthalic anhydride. 2) Coumarin derivatives are
known as useful laser dyes, however, unsubstituted coumarin emits
little fluorescence. The two-photon decarbonylation reaction
of coumarin was observed with a VUV laser. The triplet state
of coumarin did not participate in the decomposition reaction.
The hot coumarin acted as an intermediate in the multiphoton
reaction. The subsequent second photon absorption by hot coumarin
would be necessary to overcome the activation energy of the decomposition
reaction. New photochemical reactions are expected for the hot
molecule as an intermediate in multiphoton reactions.
- A summary of recent hot molecule
chemistry in our laboratory.
- DOMESTIC MEETINGS
- ･Bunsikouzou Sougou Touronkai (Poster)
- "Multiphoton dissociation of 2,2,2-paracyclophane
by hot molecule mechanism"
- Tomoyuki Yatsuhashi, Ken Ohtakeyama, Yuriko Hosoi, Seiji Shimizu, Nobuaki
Nakashima
- (Osaka Univ. Sep27-30)
- Photodissociation of gaseous 2,2,2-paracyclophane
(3PCP) was observed by an ArF laser excitation. The formation
of p-quinodimethane was clearly observed as in the case of 2,2-paracyclophane
(2PCP). The difference in the photolysis of those compound was
found in the transient absorption spectra. The precursor radical
may be observed in the case of 3PCP due to the relatively low
vibrational temperature than 2PCP. The RRKM calculation and foreign
gas pressure effect revealed that the dissociation of 3PCP was
taken place with three photon process. The hot molecule mechanism
was found valid even in the case of 3PCP which is the largest
molecule ever examined.
- Manuscript was submitted to
J. Phys. Chem. A
- ･Hikari Kagaku Touronkai (Poster)
- "ArF laser flash photolysis of gaseous
diphenyl alkanes"
- Tomoyuki Yatsuhashi, Nobuaki Nakashima
- (Okayama Univ. Sep16-18)
- The photodecomposition of the gaseous diphenyl
alkanes, such as biphenyl, diphenyl methane, and diphenyl ethane
were studied by the ArF excimer laser photolysis. Both the triplet
state and radical cation were not observed in the transient absorption
spectra, while the formation of the related radicals were clearly
observed. The formation of the radicals were proportional to
the square of the laser fluence except biphenyl. The addition
of foreign gas effectively suppressed the formation of radicals.
All the results indicated that the hot molecule was an intermediate
in the two-photon decomposition reaction of diphenyl alkanes.
- Manuscript in preparation.
- ･76th National Meeting of the Chemical Society
of Japan (ORAL)
- "Two-photon reaction via hot coumarin
by ArF excimer laser"
- Tomoyuki Yatsuhashi, Nobuaki Nakashima
- (Kanagawa Univ. Mar 28-31)
- Laser flash photolysis of gaseous coumarin
by ArF excimer laser was carried out. The observed transient
does not correspond to the triplet absorption of coumarin, and
fluorescence was not observed. The product yield was significantly
suppressed in the presence of a foreign gas. The product yield
was proportional to the square of laser fluence. All the results
suggest that the product is derived from highly vibrationally
excited states of coumarin (hot coumarin). The absorption of
second photon by hot coumarin may result in the decomposition
of coumarin. The vibrational temperature of coumarin was calculated
as 2500K (1 photon absorption) and 4200K (two photon absorption).
- See more details: J. Phys.
Chem. A 2000, 10 (6), 1095-1099.