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Far infrared spectrum of crystalline carbon disulphide
CHEMICAL PHYSICS LETTERS
Volume 45, number 3
FAR
INFRARED
SPECTRUM
OF CRYSTALLINE
CARBON
1 February
1977
DISULPHIDE
Kimihiro ISHI and Shin-i&i TAKAHASHI Research Institute for Scientific Measurements, Received 28 September
Tohoku University, Sendai, Japan
1976
The far infrared spectrum of crystalline carbon disulphide has been measured at about 1.8 K. Two absorption bands are observed, with maxima at 66.5 and 68.2 cm-‘, respectively, and with nearly equal intensities. They are considered to be due to ?he two infrared active translational modes expected by lattice dynamics.
The crystal structure of CS2 was determined by Baenziger and Dua.. in 1968 [I] _The crystal is orthorhombic and belongs to the space group Di! (Cmca) with two molecc!es in the primitive unit cell. The symmetry of the lattice sites is C&_ The structure is shown in fig. l_ From this orthorhombic structure, two infrared active translational modes are expected by lattice dynamics. Far infrared spectra of crystalline CS2 were already measured by Chantry et al. [2] at 130 K in 1967, and by Anderson et al. [3j at 79 and 18 K in 1973. In both cases, however, the absorption band observed at 66 cm-l was only one of the two expected translational modes. The aims of this work are to obtain a more detai!ed far infrared spectrum and to extend these measureC
Q
Q D +
a a -9
dBa Q
D + Fig. 1. Structure of CS2 ; open circles indicate molecules ai y = 0, full circles at y = b/2.
460
ments to lower temperatures in order to clarify the two expected infrared modes. The CS, used in this experiment was obtained from the Wako Pure Chemical Industries Company. The purity was 99%. The sample was crystallized on the inner wall of the light pipe of a cooled bolometer. Firstly, suitable amount of CS2 vapour was enclosed in the light pipe at room temperature, and then liquid nitrogen was poured into the liquid nitrogen tank of the bolometer. The light pipe hanging into the liquid helium tank was gradually cooled through the air in the tank and then the sample was crystallized on the inner wall of the light pipe. After crystallization, liquid helium was poured into the helium tank of the bolometer. As the bolometer is able to work only at temperatures less than 1.8 K, it was kept in the working state by pumping out helium gas. Therefore, the temperature of the sample is considered to be about 1.8 K. The spectrum was obtained using a far infrared spectrophotometer (Hitachi Company, Fis-3). The cooled Ce bolometer was used as an infrared detector.
Theobservedspectrumis reproducedin fig.IThere are two absorption bands at 66.5 and 68.2 cm-r, respectively. When the sample was absent, no structure was recorded. The two absorption intensities are comparable as seen in fig. 2. Similar measurements have also been tried for some other samples, Merck’s chemicals of high purity and Wako’s of lower purity, in order to check the effects of impurities, but nearly the same spectra have been observed for all samples. Fig. 3
Volume 45, number 3
CHEMICALPHYSICSLETTERS
/k l.ocll+i’ -it-
r-
iYi
a ::
-I__ O-LINE
75
70
65
6C
shows the spectrum observed at 148 K as an example of the temperature dependence of the absorption. In this case, the CS2 crystal was obtained from liquid in the liquid sample cell with silicon windows by cooling gradually with liquid nitrogen, and the spectrum was recorded by the double beam method. The absorption band shown in fig. 3 looks to be slightly asymmetric. The half-intensity width of the absorption band varies considerably with temperature. For instance, it is about 2.0 cm-l for the double bands observed at 1.8 K, and about 6.5 and 11.5 cm-l for the single bands observed at 100 and 160 K, respectiveiy. The spread in the band width must have made it difficult to separate the two modes. Ahhough no structural data of CS3 at very
0.9cllr’
d--
Ii 30 70 50 ‘AVMWBERkrt
WAVENUMEERkd)
Fig. 2. Typical spectrum of crystalline CS2 at 1.8 K.
1 February 1977
Fig. 3. Unresolved spectrum of crystalline CS2 at L48 K.
low temperature have been reported, these two absorption bands seem to be due to the two infrared active translational modes which have been only expected until now.
References [l] N.C. Baenziger and W-L. DUZK,I. Chem. Phys. 48 (L968) 2974. [2] G.W. Chantry, H.A. Gebbie, B. Lassier and G. Wylie, Nature 214 (1967) 163. [3] A. Anderson, PJ. Grout, J.W. Leech and T.S. Sun, Chem. Phys Letters 21(1973) 9.
461
Volume 45, number 3
FAR
INFRARED
SPECTRUM
OF CRYSTALLINE
CARBON
1 February
1977
DISULPHIDE
Kimihiro ISHI and Shin-i&i TAKAHASHI Research Institute for Scientific Measurements, Received 28 September
Tohoku University, Sendai, Japan
1976
The far infrared spectrum of crystalline carbon disulphide has been measured at about 1.8 K. Two absorption bands are observed, with maxima at 66.5 and 68.2 cm-‘, respectively, and with nearly equal intensities. They are considered to be due to ?he two infrared active translational modes expected by lattice dynamics.
The crystal structure of CS2 was determined by Baenziger and Dua.. in 1968 [I] _The crystal is orthorhombic and belongs to the space group Di! (Cmca) with two molecc!es in the primitive unit cell. The symmetry of the lattice sites is C&_ The structure is shown in fig. l_ From this orthorhombic structure, two infrared active translational modes are expected by lattice dynamics. Far infrared spectra of crystalline CS2 were already measured by Chantry et al. [2] at 130 K in 1967, and by Anderson et al. [3j at 79 and 18 K in 1973. In both cases, however, the absorption band observed at 66 cm-l was only one of the two expected translational modes. The aims of this work are to obtain a more detai!ed far infrared spectrum and to extend these measureC
Q
Q D +
a a -9
dBa Q
D + Fig. 1. Structure of CS2 ; open circles indicate molecules ai y = 0, full circles at y = b/2.
460
ments to lower temperatures in order to clarify the two expected infrared modes. The CS, used in this experiment was obtained from the Wako Pure Chemical Industries Company. The purity was 99%. The sample was crystallized on the inner wall of the light pipe of a cooled bolometer. Firstly, suitable amount of CS2 vapour was enclosed in the light pipe at room temperature, and then liquid nitrogen was poured into the liquid nitrogen tank of the bolometer. The light pipe hanging into the liquid helium tank was gradually cooled through the air in the tank and then the sample was crystallized on the inner wall of the light pipe. After crystallization, liquid helium was poured into the helium tank of the bolometer. As the bolometer is able to work only at temperatures less than 1.8 K, it was kept in the working state by pumping out helium gas. Therefore, the temperature of the sample is considered to be about 1.8 K. The spectrum was obtained using a far infrared spectrophotometer (Hitachi Company, Fis-3). The cooled Ce bolometer was used as an infrared detector.
Theobservedspectrumis reproducedin fig.IThere are two absorption bands at 66.5 and 68.2 cm-r, respectively. When the sample was absent, no structure was recorded. The two absorption intensities are comparable as seen in fig. 2. Similar measurements have also been tried for some other samples, Merck’s chemicals of high purity and Wako’s of lower purity, in order to check the effects of impurities, but nearly the same spectra have been observed for all samples. Fig. 3
Volume 45, number 3
CHEMICALPHYSICSLETTERS
/k l.ocll+i’ -it-
r-
iYi
a ::
-I__ O-LINE
75
70
65
6C
shows the spectrum observed at 148 K as an example of the temperature dependence of the absorption. In this case, the CS2 crystal was obtained from liquid in the liquid sample cell with silicon windows by cooling gradually with liquid nitrogen, and the spectrum was recorded by the double beam method. The absorption band shown in fig. 3 looks to be slightly asymmetric. The half-intensity width of the absorption band varies considerably with temperature. For instance, it is about 2.0 cm-l for the double bands observed at 1.8 K, and about 6.5 and 11.5 cm-l for the single bands observed at 100 and 160 K, respectiveiy. The spread in the band width must have made it difficult to separate the two modes. Ahhough no structural data of CS3 at very
0.9cllr’
d--
Ii 30 70 50 ‘AVMWBERkrt
WAVENUMEERkd)
Fig. 2. Typical spectrum of crystalline CS2 at 1.8 K.
1 February 1977
Fig. 3. Unresolved spectrum of crystalline CS2 at L48 K.
low temperature have been reported, these two absorption bands seem to be due to the two infrared active translational modes which have been only expected until now.
References [l] N.C. Baenziger and W-L. DUZK,I. Chem. Phys. 48 (L968) 2974. [2] G.W. Chantry, H.A. Gebbie, B. Lassier and G. Wylie, Nature 214 (1967) 163. [3] A. Anderson, PJ. Grout, J.W. Leech and T.S. Sun, Chem. Phys Letters 21(1973) 9.
461