ハロゲン化エチレンの光化学

1P-033（横浜国大院・工）上門 瞳 ， 横 手 祐 一，關 金 一

Photochemistry of haroethylenes(Yokohama National Univ.) Hitomi KAMIKADO, Yuichi YOKOTE, Kanekazu SEKI
【Introduction】The photochemistry of haroethylenes(HEs) in gas phase was extensively studied.
C2H2, HC2X, HX, X （X；halogen atoms）are principally observed as products. Behavior ofphotoproducts was substantially studied in terms of kinetics, but the photodissociation pathways were
not explicitly understood. It requires observation of intermediates to clarify the pathways.
A study of the photochemistry in solid phase is also useful for elucidation of the photodissociation ingas phase. Previously we reported that no C2H2 from photolysis of dichroloethylenes (DCEs) in solid
phase was observed. Although the report provided some information of a Cl dissociation channel, weanalyzed the photoproducts using indirect methods. A further research of in-situ spectroscopic data isnecessary to reveal the mechanism for the dissociation channel.
In this work we try to explain the photodissociation pathways and the photochemistry of
haroethylenes in solid phase using FTIR in-situ observation.
【Experimental】 Gaseous mixtures of HEs/Ar (1/2000) were deposited onto a CsI substrate held at
18K before photolysis. For irradiation, a 193nm ArF excimer laser was employed. After irradiation of
matrix samples, the substrate was raised the temperature annealing samples. IR absorption spectra wererecorded at various stages of experiments with FT-IR spectrometer. Spectra were collected between
4000 and 400 cm-1 with a resolution of 0.25cm-1.
【Results and Discussion】
Fig.1 shows typical IR absorption spectra (730-770cm-1) after the photolysis of HEs.
Absorbance

0.05

trans-DCE

HC2Cl-HCl [1]BA

HC2Cl-HCl [2]AbsorbanceAbsorbanceAbsorbance
/ [－]

0.00
0.05

cis-DCEHC2Cl-HCl [1]C2H2

1,1-DCEHC2Cl-HCl [1]

C2H2

0.00
0.05

0.00
770

760

750
Wavenumbers (cm-1)
Wavenumbers/ cm-1

740

Figure 1. IR absorption spectra (730-770cm-1) after the photolysis of DCEs/Ar (1/2000) at 18K.

C2H2 and HC2Cl were observed as photoproducts from cis- and 1,1-DCE. Photoproducts fromtrans-DCE included intermediates or unknown species. C2H2 and HC2Cl were assigned by comparison
with IR spectra of those in Ar matrix.
But there was a slight difference
between IR spectrum of HC2Cl as thephotoproducts and of HC2Cl in Ar
matrix. We calculated the energies,
equilibrium

structures,vibrationalwavenumbers and IR intensities ofHC2Cl-HCl

complexes

usingGaussian03. The calculations showthat the IR spectra of HC2Cl wereHC2Cl-HCl [2]HC2Cl-HCl [1]Figure 2. Geometry of HC2Cl-HCl [1] and HC2Cl-HCl [2]sifted by forming complexes (Fig.2). HC2Cl-HCl [1] from photolysis of all of the DCEs formedhydrogen-bonded π complexes, and HC2Cl-HCl [2] from only photolysis of trans-DCE formed
chlorine-bonded π complexes. Therefore we proposed that HCl elimination process in the trans-DCE
may be different from the process in the cis- and 1,1-DCE.
IR peaks A and B in Fig.1 observed as unassigned ones. In order to identify these peaks we
calculated vibrational wavenumbers of carbene as is the case in the assignments of HC2Cl peaks. The
calculations show that the carbene intermediates have the IR peaks in regions 700-800 cm-1. A further
research is necessary for assignments ofpath to the carbene between trans-DCE
and other DCEs reported in a previouswork.
IR intensity of C2H2 decreased after
raising the temperature of the CsI

Absorbanceunreliably correlates with a different

Absorbance / [－]from only photolysis of the trans-DCE

Absorbancepeaks A and B. The detection of carbene

(a)

T≒18K
HC2Cl-HCl [1]

(b)

T≒40K

0.02

C2H20.00
0.02

HC2Cl-HCl [1]

0.00
760

740
Wavenumbers / cm-1
Figure 3. (a) IR spectrum of cis-DCE/Ar
Wavenumbers (cm-1)

substrate up to 40K following thephotolysis (Fig. 3). The decreasing of IR
intensity may be due to reaction between
C2H2 and chlorine atom which is
produced from the photolysis of DCEs.

(1/2000) at 18K after the photolysis, and (b) thespectrum after raising the temperature of thesubstrate up to 40K following photolysis at 18K【Conclusion】
FTIR in-situ observation for Ar matrix photoproducts shows that the photodissociation paths ofDCEs in Ar matrix is different between trans-DCE and other DCEs.