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Diode laser spectrum of OCS in a dc discharge
JOURNAL
OF MOLECULAR
SPECTROSCOPY
99,479-48
1 (1983)
Diode Laser Spectrum of OCS in a dc Discharge During the last few years unstable molecular species such as radicals, ions, and highly excited states were detected by both microwave and high-resolution infrared spectroscopy in plasmas excited by dc and rf discharges. In the present paper we report new OCS spectra, observed in highly excited vibrational states. mostly assigned to the 2O”O-1O”O “hot” band, centered around 2040 cm-‘. OCS was excited in a glow tube powered by a dc discharge, and was detected with a slightly modified version of our tunable diode laser spectrometer, discussed earlier (I). The lo-cm diameter, 150-cm-long glass discharge tube is similar to the one used by Woods (2) for the generation of molecular radicals. It contains on both ends stainless steel hollow cylinder electrodes, separated by 120 cm. The laser beam is fed through NaCl windows, and traverses the plasma in a single path alignment before detection. The Doppler-limited spectra were recorded in second derivative form employing source modulation. We applied the dc discharge (-4 kV, - 15 mA) to a flowing OCS/argon, OCS/N2, or OCS/N,O mixture at low pressure, total -0.3 mbar with a mixing ratio of l/l yielding a stable glow discharge. We detected about 30 new but weak lines, which indicated that levels up to IOr’ were populated during discharge conditions. Figure 1 shows a portion of a spectrum obtained in gas discharge with OCS. Although most of the lines observed in this work were known transitions arising from the levels populated under room temperature conditions (j), several new lines (marked by x in Fig. 1) appeared during action of the dc discharge. Nearly all of the discharge-excited lines could be assigned to the hot band 20r’O-10’0 of OCS, which was observed for the first time by the present study. With the aid of the OCS fundamental line positions obtained
FIG. 1. A part of the u, band of OCS in a glow discharge observed by a tunable diode laser spectrometer. The spectra were recorded in the second derivative form. The lines marked by x were observed only when the discharge was on.
479
0022-2852183 Copyright
0
$3.00
1983 by Academic
All rights of reproduction
Press. Inc
I” any form
reserved.
480
NOTES TABLE I Transition Wavenumbers for the 20°0-10’0 Band of OCS R(J)
calculated
R(l0) R(l1) R(12) R(13) R(14)
2043.4626 2043.8368 2044.2085 2044.5779 2044.9448
R(15) R 16) R 17) R 18) R 19)
2045.3092 2045.6713 2046.0308 2046.3880 2046.7427
0.0013
R R R R R
20) 21) 22)
-0.0007
24)
2047.0950 2047.4448 2047.7922 2048.1371 2048.4796
R R R R R
25) 26) 27) 28) 29)
2048.8196 2049.1571 2049.4923 2049.8249 2050.1551
R R R R R
30) 31) 32) 33) 34)
23j
R(35) R(36) R(37) R(38) R(39)
o-c
0.0000
-0.0014 0.0002
R(J)
calculated
o-c
R(40) R(41) ~(42) R(43) R(44)
2053.6247 2053.9253 2054.2234 2054.5190 2054.X121
0.0001 o.onoo 0.0002 0.0013
R(45) R(46) Q(47) R(48) R(49)
2055.1027
-0.oon1
2055.3909
-0.0001 -0.0003
R(50) R(51) R(52) R(53) R(54)
2055.6766 2055.9597 2056.2404
-0.0004 0.0003
2056.5186 2056.7942
0.0000
2057.0674 2057.3381 2057.6062
R(55) R(56) R(57) R(58) R(59)
2057.8719 2058.1350 2058.3957 2058.6538 2058.9094
2050.4829 2050.8082 2051.1310 2051.4513 2051.7692
R(60) R(61) R(62) R(63) R(64)
2059.1625 2059.4130 2059.6610 2059.9065 2060.1495
-0.0002 -0.0003 -0.0002
2052.0847 2ti52.3976 2052.7081 2053.0161 2053.3216
R(65) R(66) Q(67) R(68) R(69)
2060.3899 2060.6270 2060.8632 2061.0960 2061.3263
0.0008
-0. on03 0.0002
0.0006 -0.0009 -0.0002
by Guelachvili (4) we could calibrate these newly observed lines with an accuracy of better than 0.0008 cm-‘. Table I contains the measured wavenumbers of this band. The spectroscopic parameters for this band were obtained by a least squares fit and are listed in Table II. The value of the band origin agrees very well with the value predicted from the frequency of the overtone band 2v, measured by Fayt (5) and the frequency of the fundamental band Y, (4): TABLE II Spectroscopic Parameters for the Band 2O“O-lOoOn IR + MWb)
IR only
J
"Wb)
only
2039.18626(22)
2039.18503(24)
B' B"
0.20043272(23) 0.201641413(4S)c)
0.200434289(47) 0.201641530(41)
0.20043436(33) 0.20164156(10)
D' D '*
0.044930(51) 0.044034(28)c):::"
O.O4486(23)xlOI; 0.04363(24)x10
-6 o.n45(3)xlo -6 0.0437(3)x10
vO
-1 into . Converting_lthe frequency a) All values are given in cm lcm = 29979.2450 MHz. wavenumber we used the relation in unit The numbers in parentheses are one standard deviation of the last digit.
b) Ref.@) c) Ref.(d).
Fixed
in the least
squares
fit.
1
J
481
NOTES 2v, - Y, = 2039.186(3) cm-‘.
The first column of Table II gives the results of the present analysis, where we fixed the value of the lower state, u, = 1, to the rotational constants B and D determined by Guelachvili (4). Recently Bogey and Bauer (6) measured the microwave spectra of OCS in highly excited states using rf discharge and excitation by activated nitrogen. Agreement between our results and those of Bogey and Bauer is within three times the standard deviation as shown in Table II for the u, = 2 excited vibrational state. Perhaps better agreement may be obtained with the inclusion of more lines, especially lines of the P branch. The combination of the ir data with the microwave data of Bogey and Bauer, however, resulted in excellent values for the rotational constants as listed in Table II. ACKNOWLEDGMENT This work was supported bereich 131.
in part by the Deutsche Forschungsgemeinschaft,
Sonderforschungs-
REFERENCES 1. K. YAMADA AND G. WINNEWISSER, Z. Naturjksch. 36a, 23-29 (1981). 2. R. C. WOODS, Rev. Sci. Instrum. 44,282-288 (1973). 3. W. KLEBSCH, K. YAMADA, AND G. WINNEWISSER, Z. Naturforsch. 38a, 157-162 (1983). 4. G. GUELACHVILL Opt. Commun. 30, 361-363 (1979). 5. A. F‘AYT, Ann. Sot. Sci. Bruxelles Ser. I 84, 69-106 (1970). 6. M. B~CEY AND A. BAUER, J. Mol. Spectrosc. 84, 170-178 (1980).
W.
KLEB~~H
KOICHI YAMADA G. WINNEWISSER
I. Ph_vsikalisches Institut Universitiit zu Kiiln Ziilpicher Strasse 77 D-5000 Kiiln 41 West Germany Received February 3, I983
OF MOLECULAR
SPECTROSCOPY
99,479-48
1 (1983)
Diode Laser Spectrum of OCS in a dc Discharge During the last few years unstable molecular species such as radicals, ions, and highly excited states were detected by both microwave and high-resolution infrared spectroscopy in plasmas excited by dc and rf discharges. In the present paper we report new OCS spectra, observed in highly excited vibrational states. mostly assigned to the 2O”O-1O”O “hot” band, centered around 2040 cm-‘. OCS was excited in a glow tube powered by a dc discharge, and was detected with a slightly modified version of our tunable diode laser spectrometer, discussed earlier (I). The lo-cm diameter, 150-cm-long glass discharge tube is similar to the one used by Woods (2) for the generation of molecular radicals. It contains on both ends stainless steel hollow cylinder electrodes, separated by 120 cm. The laser beam is fed through NaCl windows, and traverses the plasma in a single path alignment before detection. The Doppler-limited spectra were recorded in second derivative form employing source modulation. We applied the dc discharge (-4 kV, - 15 mA) to a flowing OCS/argon, OCS/N2, or OCS/N,O mixture at low pressure, total -0.3 mbar with a mixing ratio of l/l yielding a stable glow discharge. We detected about 30 new but weak lines, which indicated that levels up to IOr’ were populated during discharge conditions. Figure 1 shows a portion of a spectrum obtained in gas discharge with OCS. Although most of the lines observed in this work were known transitions arising from the levels populated under room temperature conditions (j), several new lines (marked by x in Fig. 1) appeared during action of the dc discharge. Nearly all of the discharge-excited lines could be assigned to the hot band 20r’O-10’0 of OCS, which was observed for the first time by the present study. With the aid of the OCS fundamental line positions obtained
FIG. 1. A part of the u, band of OCS in a glow discharge observed by a tunable diode laser spectrometer. The spectra were recorded in the second derivative form. The lines marked by x were observed only when the discharge was on.
479
0022-2852183 Copyright
0
$3.00
1983 by Academic
All rights of reproduction
Press. Inc
I” any form
reserved.
480
NOTES TABLE I Transition Wavenumbers for the 20°0-10’0 Band of OCS R(J)
calculated
R(l0) R(l1) R(12) R(13) R(14)
2043.4626 2043.8368 2044.2085 2044.5779 2044.9448
R(15) R 16) R 17) R 18) R 19)
2045.3092 2045.6713 2046.0308 2046.3880 2046.7427
0.0013
R R R R R
20) 21) 22)
-0.0007
24)
2047.0950 2047.4448 2047.7922 2048.1371 2048.4796
R R R R R
25) 26) 27) 28) 29)
2048.8196 2049.1571 2049.4923 2049.8249 2050.1551
R R R R R
30) 31) 32) 33) 34)
23j
R(35) R(36) R(37) R(38) R(39)
o-c
0.0000
-0.0014 0.0002
R(J)
calculated
o-c
R(40) R(41) ~(42) R(43) R(44)
2053.6247 2053.9253 2054.2234 2054.5190 2054.X121
0.0001 o.onoo 0.0002 0.0013
R(45) R(46) Q(47) R(48) R(49)
2055.1027
-0.oon1
2055.3909
-0.0001 -0.0003
R(50) R(51) R(52) R(53) R(54)
2055.6766 2055.9597 2056.2404
-0.0004 0.0003
2056.5186 2056.7942
0.0000
2057.0674 2057.3381 2057.6062
R(55) R(56) R(57) R(58) R(59)
2057.8719 2058.1350 2058.3957 2058.6538 2058.9094
2050.4829 2050.8082 2051.1310 2051.4513 2051.7692
R(60) R(61) R(62) R(63) R(64)
2059.1625 2059.4130 2059.6610 2059.9065 2060.1495
-0.0002 -0.0003 -0.0002
2052.0847 2ti52.3976 2052.7081 2053.0161 2053.3216
R(65) R(66) Q(67) R(68) R(69)
2060.3899 2060.6270 2060.8632 2061.0960 2061.3263
0.0008
-0. on03 0.0002
0.0006 -0.0009 -0.0002
by Guelachvili (4) we could calibrate these newly observed lines with an accuracy of better than 0.0008 cm-‘. Table I contains the measured wavenumbers of this band. The spectroscopic parameters for this band were obtained by a least squares fit and are listed in Table II. The value of the band origin agrees very well with the value predicted from the frequency of the overtone band 2v, measured by Fayt (5) and the frequency of the fundamental band Y, (4): TABLE II Spectroscopic Parameters for the Band 2O“O-lOoOn IR + MWb)
IR only
J
"Wb)
only
2039.18626(22)
2039.18503(24)
B' B"
0.20043272(23) 0.201641413(4S)c)
0.200434289(47) 0.201641530(41)
0.20043436(33) 0.20164156(10)
D' D '*
0.044930(51) 0.044034(28)c):::"
O.O4486(23)xlOI; 0.04363(24)x10
-6 o.n45(3)xlo -6 0.0437(3)x10
vO
-1 into . Converting_lthe frequency a) All values are given in cm lcm = 29979.2450 MHz. wavenumber we used the relation in unit The numbers in parentheses are one standard deviation of the last digit.
b) Ref.@) c) Ref.(d).
Fixed
in the least
squares
fit.
1
J
481
NOTES 2v, - Y, = 2039.186(3) cm-‘.
The first column of Table II gives the results of the present analysis, where we fixed the value of the lower state, u, = 1, to the rotational constants B and D determined by Guelachvili (4). Recently Bogey and Bauer (6) measured the microwave spectra of OCS in highly excited states using rf discharge and excitation by activated nitrogen. Agreement between our results and those of Bogey and Bauer is within three times the standard deviation as shown in Table II for the u, = 2 excited vibrational state. Perhaps better agreement may be obtained with the inclusion of more lines, especially lines of the P branch. The combination of the ir data with the microwave data of Bogey and Bauer, however, resulted in excellent values for the rotational constants as listed in Table II. ACKNOWLEDGMENT This work was supported bereich 131.
in part by the Deutsche Forschungsgemeinschaft,
Sonderforschungs-
REFERENCES 1. K. YAMADA AND G. WINNEWISSER, Z. Naturjksch. 36a, 23-29 (1981). 2. R. C. WOODS, Rev. Sci. Instrum. 44,282-288 (1973). 3. W. KLEBSCH, K. YAMADA, AND G. WINNEWISSER, Z. Naturforsch. 38a, 157-162 (1983). 4. G. GUELACHVILL Opt. Commun. 30, 361-363 (1979). 5. A. F‘AYT, Ann. Sot. Sci. Bruxelles Ser. I 84, 69-106 (1970). 6. M. B~CEY AND A. BAUER, J. Mol. Spectrosc. 84, 170-178 (1980).
W.
KLEB~~H
KOICHI YAMADA G. WINNEWISSER
I. Ph_vsikalisches Institut Universitiit zu Kiiln Ziilpicher Strasse 77 D-5000 Kiiln 41 West Germany Received February 3, I983