2000
- INTERNATIONAL MEETING
- ・XVIII IUPAC Symposium on Photochemistry (POSTER)
- "Hot Molecule as an Intermediate in Multiphoton
Reactions"
- Tomoyuki Yatsuhashi, Nobuaki Nakashima
- （Germany, Jul. 22-27）
- In this study, some examples of hot molecule
chemistry will be presented with respect to multiphoton reactions
of gaseous alkylarenes. All the experiments were performed at
high temperature (~ 520 K) to obtain sufficient vapor pressure
and photolyzed by an ArF excimer laser. In the transient absorption
spectra of alkylarenes, the triplet state and cation radical
as well as emission were not observed. The transient spectra
within the laser pulse width were well simulated by the theoretical
model for hot molecule spectra. The neutral radical formation
was proportional to the square or cubic of the laser fluence.
All the results show that the radicals were formed by the multiphoton
reaction of hot molecule in all alkylarenes examined. Although
alkylarenes were decomposed by multiphoton processes both in
the condensed and in the gas phase, the decomposition mechanisms
were very much different. The photolysis may be the most easiest
way of radical production, however, a neutral radical formation
by a strong laser light is not easy in the condensed phase because
the multiphoton absorption by the electronic excited state would
take place easily and cation radical will be formed. The formation
of neutral radicals were explained in terms of the deprotonation
of radical cation which was formed by the two-photon process
in the condensed phase. On the other hand, the radicals were
formed thermally after the second or third photon absorption
by hot molecule in the gas phase.
- Manuscript in preparation
- DOMESTIC MEETINGS
- ･Hikari Kagaku Touronkai (ORAL)
- (Hokkaido Univ. Sep16-18)
- "Two-Photon Reaction of Biphenylene via
Highly Vibrationally Excited State"
- Tomoyuki Yatsuhashi, Tsuyoshi Akiho, Nobuaki Nakashima
- The first photo-induced reaction of biphenylene
was found. Biphenylene (BP) have been deemed to be photoinert
molecule, because the internal conversion yield was estimated
to be almost unity. BP has attracted attentions of physical chemists
due to its anonymous physical properties, whereas the
so called ﾒdark moleculeﾓ was out of interest for photochemist.
However, the high internal conversion yield means that the efficient
formation of vibrationally hot molecule which has a large molar
extinction coefficient in VUV region. The multiphoton absorption
by a vibrationally hot molecule induced the dissociation reaction.
The multiphoton hot molecule mechanism sheds light on the molecules
which have been thought to be photoinert.
- See details: J. Am. Chem. Soc.
2001, 123 (41), 10137-10138.
- ･78th National Meeting of the Chemical Society
of Japan (ORAL)
- "First Three-photon process via vibrationally
hot molecule: dissociation of triphenylmethane"
- Tomoyuki Yatsuhashi, Nobuaki Nakashima
- (Nihon Univ. Mar 28-31)
- Laser flash photolysis of gaseous triphenylmethane
(TPM) by an ArF excimer laser resulted in the formation of TPM
radical. The triplet state and cation radical, and fluorescence
was not observed. TPM radical formation was suppressed by a foreign
gas and the yield was proportional to the cubic of laser fluence.
The dissociation rate constant was estimated on the basis of
RRKM theory, and it predicted that the dissociation reaction
requires at least three photon absorption. All the results suggest
that the TPM radical is derived from highly vibrationally excited
TPM.
- See details: J. Phys. Chem.
A 2000, 104(46), 10465-10467.