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Direct observation of the twisting vibration in tetrachloroethylene through the hyper-Raman effect
CHEMICAL PHYSICS LETTERS
Volume 45, number 3
DIRECT OBSERVATION OF THE TWISTING VIBRATION THROUGH
THE HYI’ER-RAMAN
I February 1977
IN TETRACHLOROETHYLENE
EFFECT*
W.J. SCHMID and H.W. SCHR@KTER Se&ion Physik der Universit& Minchm,
08000
Mmich 40, Germany
Received 19 October 1976
The hyper-Raman spectrum of liquid C2Cl4 was recorded with Nd-YAG laser excitation and single channel detection. the Raman and infrared inactive twisting vibration v4(au) was observed
In addition to the known infrared active vibrations at 106 + 3 cm-‘.
‘ihe hyper-Raman effects allows the direct observation of fundamental vibrations of molecules and crystals which are both infrared and Raman inactive [l] . The selection rules were group theoretically derived for all molecular point groups [Z-4] _ In previousIy published experimental investigations of the hyperRaman effect in liquids [5,6] only also infrared active vibrations were studred; however, the detection of mactive vibrations in benzene was reported by Maker [7] two years ago. ln high pressure ethane and ethylene [8] indications of inactive vibrations were found,
but the resolution was inadequate for precise wavenumber determinations. So it can be said that only the inactive librationd mode in an NHaCl crystal [9,10] has been well established in the literature. The vibrational spectrum of tetrachloroethylene CzC14 was the subject
of numerous
experimental
in-
vestigations [i 1-I 6). The wavenumber of the inactive out-of-plane twisting vibration vh(aU) was estimated to be 110 cm-* [13] and a complete set of vibrational frequencies was established through a normal coordinate analysis of the perhalogenated ethylenes [ 171. We have recorded the hyper-Raman spectrum of CZC14in order to measure the wavenumber of the v4 vibration directly. The spectra were excited by an acousto-optically Q-switched Nd-YAG laser from MBB, * Presented as post-deadline paper at the Sth International Conference on Raman Spectroscopy, Freiburg, September
8, 1976.
502
Munich, giving SO00 p&es per second of about 4 mJ, and recorded by a conventional Raman spectrometer (Spex 14018) coupled to a PDF1 1 computer system [ 181. The puises coming from the photomultiplier (C 3 1034 A-02 cooled to -30°C) were preamplified and fed to the input of a gateable discriminator. The gate opening time was 200 ns, the pulse width of the Nd-YAG laser about 100 ns. Through a puise delay full overlapping of the synchronized gate and laser pulses was achieved. ln this way ^Jte dark count rate was reduced from 10 cps (ungated) to 0.01 cps in the gated mode. The signal pulses were fed to the counting input of the PDP-I 1 for storage and further processing. Fig. la shows the hyper-Raman spectrum of a mixture of 75% CzCI4 and 2.5% CCI,. Carbon tetrachloride was added in order to be able to optimize the optical adjustment using the hyper-Rayleigh line of CC14 which gave a comparatively high count rate, as can be seen in fig. 1b. Four bands are clearly discernible in the hyperRaman spectrum of C, Cl,, with peak positions at 105, 285,780 and 905 cm-l, A shoulder at 310 cm-l and most of the intensity of the 780 cm-l band are due to CCL+.The bands at 285,780, and 905 cm-l coincide with the infrared active vibrations v7@ lu), Y*1(b3u), and vg(b&, whereas the 105 cm-l band appears very close to the expected position 1 IO cm-l for the inactive va(a,) fundamental. The data points were taken atScm-t intervals, our best estimate for the true peak position of v4 is 106 -+3 cm-l. The refined set of fundamental vibrations of C,Cl,
CHEMICAL PHYSfCS LETl’ERS
Volume 45, number 3
I February 1977
Table 1 Fund~rnen~
ribrations of C2C& (in cm-t)
VI v2 v3
%
58 CPS 7
=u
I
VI0
VlI VI2
10 CPL
1572
447
447
235
236
0
10)
1000 “g
btu bB
“9 CCI,
1571 I
07 “8
b)
This work
%
v4
F5
Ref. [ L7]
1
bzu
3
b3U
206 394
347 288 512 908
347 288 5f2 90s
176 777 310
176 777 309
References [l]
Fig. 1. Hyper-Raman spectra of &Cl4 and CC4 excited by Nd-YAG laser at 1064 nm, spectral slit width 12.5 cm-t. (a) 75% c2C14 + 25%CCl4, lo6 pulses of 4 mJ per data point (200 s sampling time) every 5 cm-‘, total scanning time 11.5 h. (b) Pure CCb, 5 X 10’ pulses of 4 mJ per data point (100 s sampling time) every 4 cm-t, total scanning time 7h. Both
spectra were smoothed giving the weigths 1,4,6,4,1
to five
successive data points.
is given in table i together with the previous set [173. Because the changes are small compared to the e?rperimental error, it is not worth while to recalculate the t~ermod~n~jc functions f19f. It should be men-
tioned at this point, that depolarization measurements in the linear Raman spectrum (161 have shown that the b,, funda~~~ntal vS must be associated with a very weak, broad depolarized Raman band at 994 cm- l, whereas the sharp line at 1004 cm-l is polarized and must be assigned as combination of symmetry $, possibly vll(b3uI * Qb2g) - v7(bl,,). We thank J. Brandmiiller for his interest in this work, W. Kiefer for suggestions and discussions, A. Beckmann for interfacing the spectrometer to the computer and W. Rometsch for his help with the measurements. The financial support from the Deutsche Fo~~hungsgemeinschaft and the Bundesministerium ftir Forschung und Technologie is gratefi.dly acknowledged.
Li Yin-Yuan, Acta Phys. Sinica 20 0964) 164. [2] S.J. Cyvin, J.E. Rauch and J.C. Decius, 5. Chem. Phys 43 (1965) 4083. (31 J.H. Christie and D.J. Lockwood, I. Chem. Phys. 54 (1971) 1141. (41 A.C. Menzies, unpubiished. [S] R.W. Terhune, P.D. Maker and C.&f_Savage, Phys. RevLetters 14 (1965) 681. 16) M.J. French and D.A. Long, J. Raman Spectry. 3 (1975) 391. [7] P.D. Maker, paper 2A at the 4th International Conference on Raman Spectroscopy, Brunswick, August L974. f8] J.F. Verdieck, S.H. Peterson, C.M_Savage and P-D. Maker, Chem. Phys. Letters 7 (1970) 2I9. [9 ] CM. Savage and P-D. Maker, Appl. Opt. 10 (I9711 965. [lo] T.J. Zmes, M-J. French, R.B.J. Hali and D.A. Long, in: Proceedings of the 5th International Conference on Raman Spectroscopy, eds. E.D. Schmid et al. (Schutt Ver&, Freiburg, 1976) p. 707. f 1 l] H. Wittek, Z. Physlk. Chem 48B (1940) 1. [12] HJ. Bernstein, I. Chem. Phys. 18 (19SO) 478[ 131 D.E. Mann, N. Acquista and E.K. Pfyfer, I. Res. NatI. Bur. Std. 52 (1954) 67. [ 141 G. Raupp, Dissertation, Univenitat Freiburg (195% _ 1151 G.E. Walrafen and J. Stone, AppL Spectry. 26 (1972) 585. [ 161 W.J. Schmid and H.W. Schriitter, to be published. 1171 D.E. Mdnn, L. Fano, J.H. Meal and T. Shimanotlchi, J. Chem. Phys. 27 (1957) 51. [ 181 A. Beckmann, W. Rometsch and IV. Riefer. to be published. [ 191 D-E. Mann, J.& Meal and E.K. Plyler, 3. Chem. Whys 24 (1956) tOt8. 503
Volume 45, number 3
DIRECT OBSERVATION OF THE TWISTING VIBRATION THROUGH
THE HYI’ER-RAMAN
I February 1977
IN TETRACHLOROETHYLENE
EFFECT*
W.J. SCHMID and H.W. SCHR@KTER Se&ion Physik der Universit& Minchm,
08000
Mmich 40, Germany
Received 19 October 1976
The hyper-Raman spectrum of liquid C2Cl4 was recorded with Nd-YAG laser excitation and single channel detection. the Raman and infrared inactive twisting vibration v4(au) was observed
In addition to the known infrared active vibrations at 106 + 3 cm-‘.
‘ihe hyper-Raman effects allows the direct observation of fundamental vibrations of molecules and crystals which are both infrared and Raman inactive [l] . The selection rules were group theoretically derived for all molecular point groups [Z-4] _ In previousIy published experimental investigations of the hyperRaman effect in liquids [5,6] only also infrared active vibrations were studred; however, the detection of mactive vibrations in benzene was reported by Maker [7] two years ago. ln high pressure ethane and ethylene [8] indications of inactive vibrations were found,
but the resolution was inadequate for precise wavenumber determinations. So it can be said that only the inactive librationd mode in an NHaCl crystal [9,10] has been well established in the literature. The vibrational spectrum of tetrachloroethylene CzC14 was the subject
of numerous
experimental
in-
vestigations [i 1-I 6). The wavenumber of the inactive out-of-plane twisting vibration vh(aU) was estimated to be 110 cm-* [13] and a complete set of vibrational frequencies was established through a normal coordinate analysis of the perhalogenated ethylenes [ 171. We have recorded the hyper-Raman spectrum of CZC14in order to measure the wavenumber of the v4 vibration directly. The spectra were excited by an acousto-optically Q-switched Nd-YAG laser from MBB, * Presented as post-deadline paper at the Sth International Conference on Raman Spectroscopy, Freiburg, September
8, 1976.
502
Munich, giving SO00 p&es per second of about 4 mJ, and recorded by a conventional Raman spectrometer (Spex 14018) coupled to a PDF1 1 computer system [ 181. The puises coming from the photomultiplier (C 3 1034 A-02 cooled to -30°C) were preamplified and fed to the input of a gateable discriminator. The gate opening time was 200 ns, the pulse width of the Nd-YAG laser about 100 ns. Through a puise delay full overlapping of the synchronized gate and laser pulses was achieved. ln this way ^Jte dark count rate was reduced from 10 cps (ungated) to 0.01 cps in the gated mode. The signal pulses were fed to the counting input of the PDP-I 1 for storage and further processing. Fig. la shows the hyper-Raman spectrum of a mixture of 75% CzCI4 and 2.5% CCI,. Carbon tetrachloride was added in order to be able to optimize the optical adjustment using the hyper-Rayleigh line of CC14 which gave a comparatively high count rate, as can be seen in fig. 1b. Four bands are clearly discernible in the hyperRaman spectrum of C, Cl,, with peak positions at 105, 285,780 and 905 cm-l, A shoulder at 310 cm-l and most of the intensity of the 780 cm-l band are due to CCL+.The bands at 285,780, and 905 cm-l coincide with the infrared active vibrations v7@ lu), Y*1(b3u), and vg(b&, whereas the 105 cm-l band appears very close to the expected position 1 IO cm-l for the inactive va(a,) fundamental. The data points were taken atScm-t intervals, our best estimate for the true peak position of v4 is 106 -+3 cm-l. The refined set of fundamental vibrations of C,Cl,
CHEMICAL PHYSfCS LETl’ERS
Volume 45, number 3
I February 1977
Table 1 Fund~rnen~
ribrations of C2C& (in cm-t)
VI v2 v3
%
58 CPS 7
=u
I
VI0
VlI VI2
10 CPL
1572
447
447
235
236
0
10)
1000 “g
btu bB
“9 CCI,
1571 I
07 “8
b)
This work
%
v4
F5
Ref. [ L7]
1
bzu
3
b3U
206 394
347 288 512 908
347 288 5f2 90s
176 777 310
176 777 309
References [l]
Fig. 1. Hyper-Raman spectra of &Cl4 and CC4 excited by Nd-YAG laser at 1064 nm, spectral slit width 12.5 cm-t. (a) 75% c2C14 + 25%CCl4, lo6 pulses of 4 mJ per data point (200 s sampling time) every 5 cm-‘, total scanning time 11.5 h. (b) Pure CCb, 5 X 10’ pulses of 4 mJ per data point (100 s sampling time) every 4 cm-t, total scanning time 7h. Both
spectra were smoothed giving the weigths 1,4,6,4,1
to five
successive data points.
is given in table i together with the previous set [173. Because the changes are small compared to the e?rperimental error, it is not worth while to recalculate the t~ermod~n~jc functions f19f. It should be men-
tioned at this point, that depolarization measurements in the linear Raman spectrum (161 have shown that the b,, funda~~~ntal vS must be associated with a very weak, broad depolarized Raman band at 994 cm- l, whereas the sharp line at 1004 cm-l is polarized and must be assigned as combination of symmetry $, possibly vll(b3uI * Qb2g) - v7(bl,,). We thank J. Brandmiiller for his interest in this work, W. Kiefer for suggestions and discussions, A. Beckmann for interfacing the spectrometer to the computer and W. Rometsch for his help with the measurements. The financial support from the Deutsche Fo~~hungsgemeinschaft and the Bundesministerium ftir Forschung und Technologie is gratefi.dly acknowledged.
Li Yin-Yuan, Acta Phys. Sinica 20 0964) 164. [2] S.J. Cyvin, J.E. Rauch and J.C. Decius, 5. Chem. Phys 43 (1965) 4083. (31 J.H. Christie and D.J. Lockwood, I. Chem. Phys. 54 (1971) 1141. (41 A.C. Menzies, unpubiished. [S] R.W. Terhune, P.D. Maker and C.&f_Savage, Phys. RevLetters 14 (1965) 681. 16) M.J. French and D.A. Long, J. Raman Spectry. 3 (1975) 391. [7] P.D. Maker, paper 2A at the 4th International Conference on Raman Spectroscopy, Brunswick, August L974. f8] J.F. Verdieck, S.H. Peterson, C.M_Savage and P-D. Maker, Chem. Phys. Letters 7 (1970) 2I9. [9 ] CM. Savage and P-D. Maker, Appl. Opt. 10 (I9711 965. [lo] T.J. Zmes, M-J. French, R.B.J. Hali and D.A. Long, in: Proceedings of the 5th International Conference on Raman Spectroscopy, eds. E.D. Schmid et al. (Schutt Ver&, Freiburg, 1976) p. 707. f 1 l] H. Wittek, Z. Physlk. Chem 48B (1940) 1. [12] HJ. Bernstein, I. Chem. Phys. 18 (19SO) 478[ 131 D.E. Mann, N. Acquista and E.K. Pfyfer, I. Res. NatI. Bur. Std. 52 (1954) 67. [ 141 G. Raupp, Dissertation, Univenitat Freiburg (195% _ 1151 G.E. Walrafen and J. Stone, AppL Spectry. 26 (1972) 585. [ 161 W.J. Schmid and H.W. Schriitter, to be published. 1171 D.E. Mdnn, L. Fano, J.H. Meal and T. Shimanotlchi, J. Chem. Phys. 27 (1957) 51. [ 181 A. Beckmann, W. Rometsch and IV. Riefer. to be published. [ 191 D-E. Mann, J.& Meal and E.K. Plyler, 3. Chem. Whys 24 (1956) tOt8. 503