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The Near-InfraredY2Σ+–X2Π Transition of CuS
Journal of Molecular Spectroscopy 195, 328 –331 (1999) Article ID jmsp.1999.7840, available online at http://www.idealibrary.com on
The Near-Infrared Y 2S 1–X 2P Transition of CuS L. C. O’Brien,* ,1 M. Dulick,† and S. P. Davis‡ *Department of Chemistry, Southern Illinois University at Edwardsville, Edwardsville, Illinois 62026-1652; †National Solar Observatory, 950 North Cherry Avenue, Tucson, Arizona 85726-6732; and ‡Department of Physics, University of California at Berkeley, Berkeley, California 94720 Received November 9, 1998; in revised form February 2, 1999
The near-infrared electronic transition of CuS has been observed for the first time. The spectrum of the Y 2 S 1 –X 2 P transition, labeled by analogy with the CuO near infrared electronic transition, was recorded with the Fourier transform spectrometer associated with the McMath–Pierce Solar Telescope, Kitt Peak, Arizona. The excited CuS molecules were produced in a King-type carbon tube furnace operating at 1900°C and at a total pressure of approximately 400 Torr. The electronic transition energy and vibrational constants for the Y 2 S 1 state of 63 Cu 32 S are presented. © 1999 Academic Press INTRODUCTION
Previous experimental work on CuS has focused on the visible electronic transitions of CuS. Transitions to the ground state from five excited states have been observed: A 2 S 2 [17.9] (1– 6), D 4 S 1/ 2 [23.1] (7), E 2 P [24.0] (8), FV 5 [1-2] [24.7] (8), and G 2P [25.0] (8). The lower-lying 2S 1 state, analogous to the Y 2 S 1 state of CuO (9, 10), was predicted by ab initio calculations (11). EXPERIMENTAL DETAILS
The excited CuS molecules were produced in a Kingtype carbon tube furnace charged with approximately 10 g of CuS powder. The tube was filled with 50 Torr helium and then heated to 1900°C, with a final pressure of 400 Torr. The CuS emission was focused onto the entrance aperture of the Fourier transform spectrometer (FTS), located at the McMath–Pierce Solar Observatory, Kitt Peak, AZ. Five scans at a resolution of 0.017 cm 21 were coadded in 42 min of integration. The spectral region 3500 cm 21 to 14 000 cm 2 1 was recorded by the FTS, which was configured with a 715-nm red-pass filter, a CaF 2 beamsplitter, and two InSb detectors with uranium glass filters. The internal FTS HeNe laser provided wavenumber calibration, and the absolute accuracy is estimated at better than 0.004 cm 21 . RESULTS AND DISCUSSION
The Y 2 S 1 –X 2 P transition of CuS was observed in emission in the 10 000 –11 000 cm 21 region of the FTS 1
To whom correspondence should be addressed. E-mail: lobrien@ siue.edu.
spectrum. A portion of the spectrum showing the Y 2 S 1 – X 2 P 1/ 2 bandheads is given in Fig. 1. The ground state rotational constant is known to be about 0.198 cm 21 , so rotational resolution was expected. For this experiment, however, the line density was extremely high for several reasons. In each subband, Y 2 S 1 –X 2 P 1/ 2 and Y 2 S 1 –X 2 P 3/ 2 , there are six branches. There are two copper isotopes ( 63 Cu at 69.17% and 65 Cu at 30.83% abundance) (12). The Y 2 S 1 state is expected to show a strong Fermi contact interaction further splitting each rotational transition into four lines (10) (nuclear spin for both copper isotopes is I Cu 5 [3-2]). The temperature is very high, enhancing the high-J lines and increasing the Doppler width almost threefold, and the pressure broadening at 400 Torr is significant (at ;100 MHz/Torr, pressure broadening is more than 1 cm 21 ). Although some rotational structure is observable in the spectrum, individual rotational lines are not resolved and a rotational analysis was not possible. As shown in Fig. 1, the spectrum is degraded to the violet, which is similar to the bands observed in the Y 2 S 1 – X 2 P spectrum of CuO (10). The P 21 , Q 21 , and P 1 bandheads are identifiable in the Y 2 S 1 –X 2 P 1/ 2 subband spectrum (see Fig. 1), and the P 2 , Q 2 , and P 12 bandheads are identifiable in the Y 2 S 1 –X 2 P 3/ 2 subband spectrum. The Q 21 and Q 2 bandheads are the strongest bandheads in each vibronic band, and the Q 21 and Q 2 bandhead peak positions were used in the fit to determine the molecular vibrational parameters of the Y 2 S 1 transition. The Q 21 and Q 2 bandheads are probably within 5 cm 21 of the origin of each subband, as was observed in CuO, and thus using the bandhead is a reasonable approximation for the
328 0022-2852/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
Y 2 S 1 —X 2 P TRANSITION OF CuS
329
FIG. 1. A portion of the Y 2 S 1 –X 2 P 1/ 2 spectrum of CuS.
transition energy of that subband. Although the spin— orbit splitting in the X 2 P state ( A 5 2433 cm 21 ) is similar in magnitude to the vibrational frequencies of the ground and excited state ( v 0e 5 414 cm 21 and v9e 5 432 cm 21 ), the vibronic bands were readily assigned using the ground state molecular parameters by Biron (1– 4) and David et al. (5). Bands were observed only in the Dv 5 0 and Dv 5 1 sequences. A total of 36 vibronic Q 2 and Q 21 bandheads were used in the fit. Vibronic transitions were observed for v9 5 0 – 6 and v 0 5 0 – 6 for 63 CuS, and v9 5 0 –5 and v 0 5 0 –5 for 65 CuS. We obtained a total of 10 molecular constants using a nonlinear least-squares fitting program. The calculated energy levels of the X 2 P 1/ 2,3/ 2 v 5 0, 1 states, obtained from the high resolution, laser-induced fluorescence spectrum of the A 2 S–X 2 P system by David et al. (5), were included in the fit and weighted appropriately by their given experimental accuracy. The average uncertainty of the Y 2 S 1 –X 2 P transitions as determined from the standard deviation of the fit is 0.08 cm 21 , which is consistent with the estimated measurement accuracy. The bandheads are wide (0.3 cm 21 ) and often lumpy, which limited our measurement accuracy.
TABLE 1 Spectroscopic Constants (in cm 21) for the X 2P and Y 2S 1 States of 63CuS
Note. One standard deviation error on the last digits is quoted in parentheses.
Copyright © 1999 by Academic Press
330
O’BRIEN, DULICK, AND DAVIS
TABLE 2 Q 21 and Q 2 Bandhead Positions, Assignments, and Fit Residuals (cm 21) for the Y 2S 1–X 2P Transition of CuS
The fitting program incorporated Dunham-type vibronic energy expressions for the 2 S 1 and 2 P states, using massindependent constants (13) E v ~ 2 S 1 ! 5 T e 1 m 21/ 2 U 10 ~v 1 12 ! 1 m 21 U 20 ~v 1 12 ! 2 1 m 23/ 2 U 30 ~v 1 12 ! 3
[1]
E v ~ 2 P! 5 m 21/ 2 U 10 ~v 1 12 ! 1 m 21 U 20 ~v 1 12 ! 2 1 m 23/ 2 U 30 ~v 1 12 ! 3 7 12 A 7 12 a A ~v 1 12 ! [2] where the upper sign refers to the X 2 P 1/ 2 spin– orbit component and the lower sign refers to the X 2 P 3/ 2 spin– orbit component. The X 2 P state is known to be inverted, A 5 2433 cm 21 (1– 8). The Dunham-type mass-dependent molecular parameters for the X 2 P and Y 2 S 1 state of 63CuS are presented in Table 1. Bandhead positions, assignments, and fit residuals are presented in Table 2. There were no significant deviations from
the expected isotopic relationships among the molecular parameters for 63CuS and 65CuS. The observed ground state state molecular constants are in good agreement with the literature values (1– 8) (see Table 1). The observed excited state transition energy and vibrational constants are in reasonable agreement with the value predicted from ab initio calculations (11) (see Table 1). The ab initio calculations (11) also predict a shorter bond upon excitation to the Y 2 S 1 state, which agrees with our violet-degraded bandheads. ACKNOWLEDGMENTS Partial support for this work was provided by the National Science Foundation’s Professional Opportunities for Women in Research and Education Program through Grant NSF-CHE-9753254.
REFERENCES 1. M. Biron, C. R. Acad. Sci., Paris, B 258, 4228 – 4230 (1964). 2. M. Biron, C. R. Acad. Sci., Paris, B 274, 978 –980 (1972).
Copyright © 1999 by Academic Press
Y 2 S 1 —X 2 P TRANSITION OF CuS 3. M. Biron, C. R. Acad. Sci., Paris, B 281, 401– 403 (1975). 4. M. Biron, C. R. Acad. Sci., Paris, B 283, 209 –212 (1976). 5. F. David, M. Douay, and Y. Lefebvre, J. Mol. Spectrosc. 112, 115–126 (1985). 6. T. C. Steimle, W.-L. Chang, and D. F. Nachman, J. Chem. Phys. 89, 7172–7179 (1988). 7. Y. Lefebvre, J. M. Delaval, and J. Schamps, Phys. Scripta 44, 355–357 (1991). 8. F. David, J. M. Delaval, and Y. Lefebvre, Phys. Scripta 31, 570 –578 (1985).
331
9. Y. Lefebvre, B. Pinchemel, J. M. Delaval, and J. Schamps, Phys. Scripta 25, 329 –332 (1982). 10. L. C. O’Brien, R. L. Kubicek, S. J. Wall, D. E. Koch, R. J. Friend, and C. R. Brazier, J. Mol. Spectrosc. 180, 365–368 (1996). 11. S. R. Langhoff and C. W. Bauschlicher, Jr., Chem. Phys. Lett. 124, 241–247 (1986). 12. “Handbook of Chemistry and Physics,” 71st ed., CRC Press, Boston, MA, 1990. 13. P. F. Bernath, “Spectra of Atoms and Molecules,” Oxford University Press, New York, 1995.
Copyright © 1999 by Academic Press
The Near-Infrared Y 2S 1–X 2P Transition of CuS L. C. O’Brien,* ,1 M. Dulick,† and S. P. Davis‡ *Department of Chemistry, Southern Illinois University at Edwardsville, Edwardsville, Illinois 62026-1652; †National Solar Observatory, 950 North Cherry Avenue, Tucson, Arizona 85726-6732; and ‡Department of Physics, University of California at Berkeley, Berkeley, California 94720 Received November 9, 1998; in revised form February 2, 1999
The near-infrared electronic transition of CuS has been observed for the first time. The spectrum of the Y 2 S 1 –X 2 P transition, labeled by analogy with the CuO near infrared electronic transition, was recorded with the Fourier transform spectrometer associated with the McMath–Pierce Solar Telescope, Kitt Peak, Arizona. The excited CuS molecules were produced in a King-type carbon tube furnace operating at 1900°C and at a total pressure of approximately 400 Torr. The electronic transition energy and vibrational constants for the Y 2 S 1 state of 63 Cu 32 S are presented. © 1999 Academic Press INTRODUCTION
Previous experimental work on CuS has focused on the visible electronic transitions of CuS. Transitions to the ground state from five excited states have been observed: A 2 S 2 [17.9] (1– 6), D 4 S 1/ 2 [23.1] (7), E 2 P [24.0] (8), FV 5 [1-2] [24.7] (8), and G 2P [25.0] (8). The lower-lying 2S 1 state, analogous to the Y 2 S 1 state of CuO (9, 10), was predicted by ab initio calculations (11). EXPERIMENTAL DETAILS
The excited CuS molecules were produced in a Kingtype carbon tube furnace charged with approximately 10 g of CuS powder. The tube was filled with 50 Torr helium and then heated to 1900°C, with a final pressure of 400 Torr. The CuS emission was focused onto the entrance aperture of the Fourier transform spectrometer (FTS), located at the McMath–Pierce Solar Observatory, Kitt Peak, AZ. Five scans at a resolution of 0.017 cm 21 were coadded in 42 min of integration. The spectral region 3500 cm 21 to 14 000 cm 2 1 was recorded by the FTS, which was configured with a 715-nm red-pass filter, a CaF 2 beamsplitter, and two InSb detectors with uranium glass filters. The internal FTS HeNe laser provided wavenumber calibration, and the absolute accuracy is estimated at better than 0.004 cm 21 . RESULTS AND DISCUSSION
The Y 2 S 1 –X 2 P transition of CuS was observed in emission in the 10 000 –11 000 cm 21 region of the FTS 1
To whom correspondence should be addressed. E-mail: lobrien@ siue.edu.
spectrum. A portion of the spectrum showing the Y 2 S 1 – X 2 P 1/ 2 bandheads is given in Fig. 1. The ground state rotational constant is known to be about 0.198 cm 21 , so rotational resolution was expected. For this experiment, however, the line density was extremely high for several reasons. In each subband, Y 2 S 1 –X 2 P 1/ 2 and Y 2 S 1 –X 2 P 3/ 2 , there are six branches. There are two copper isotopes ( 63 Cu at 69.17% and 65 Cu at 30.83% abundance) (12). The Y 2 S 1 state is expected to show a strong Fermi contact interaction further splitting each rotational transition into four lines (10) (nuclear spin for both copper isotopes is I Cu 5 [3-2]). The temperature is very high, enhancing the high-J lines and increasing the Doppler width almost threefold, and the pressure broadening at 400 Torr is significant (at ;100 MHz/Torr, pressure broadening is more than 1 cm 21 ). Although some rotational structure is observable in the spectrum, individual rotational lines are not resolved and a rotational analysis was not possible. As shown in Fig. 1, the spectrum is degraded to the violet, which is similar to the bands observed in the Y 2 S 1 – X 2 P spectrum of CuO (10). The P 21 , Q 21 , and P 1 bandheads are identifiable in the Y 2 S 1 –X 2 P 1/ 2 subband spectrum (see Fig. 1), and the P 2 , Q 2 , and P 12 bandheads are identifiable in the Y 2 S 1 –X 2 P 3/ 2 subband spectrum. The Q 21 and Q 2 bandheads are the strongest bandheads in each vibronic band, and the Q 21 and Q 2 bandhead peak positions were used in the fit to determine the molecular vibrational parameters of the Y 2 S 1 transition. The Q 21 and Q 2 bandheads are probably within 5 cm 21 of the origin of each subband, as was observed in CuO, and thus using the bandhead is a reasonable approximation for the
328 0022-2852/99 $30.00 Copyright © 1999 by Academic Press All rights of reproduction in any form reserved.
Y 2 S 1 —X 2 P TRANSITION OF CuS
329
FIG. 1. A portion of the Y 2 S 1 –X 2 P 1/ 2 spectrum of CuS.
transition energy of that subband. Although the spin— orbit splitting in the X 2 P state ( A 5 2433 cm 21 ) is similar in magnitude to the vibrational frequencies of the ground and excited state ( v 0e 5 414 cm 21 and v9e 5 432 cm 21 ), the vibronic bands were readily assigned using the ground state molecular parameters by Biron (1– 4) and David et al. (5). Bands were observed only in the Dv 5 0 and Dv 5 1 sequences. A total of 36 vibronic Q 2 and Q 21 bandheads were used in the fit. Vibronic transitions were observed for v9 5 0 – 6 and v 0 5 0 – 6 for 63 CuS, and v9 5 0 –5 and v 0 5 0 –5 for 65 CuS. We obtained a total of 10 molecular constants using a nonlinear least-squares fitting program. The calculated energy levels of the X 2 P 1/ 2,3/ 2 v 5 0, 1 states, obtained from the high resolution, laser-induced fluorescence spectrum of the A 2 S–X 2 P system by David et al. (5), were included in the fit and weighted appropriately by their given experimental accuracy. The average uncertainty of the Y 2 S 1 –X 2 P transitions as determined from the standard deviation of the fit is 0.08 cm 21 , which is consistent with the estimated measurement accuracy. The bandheads are wide (0.3 cm 21 ) and often lumpy, which limited our measurement accuracy.
TABLE 1 Spectroscopic Constants (in cm 21) for the X 2P and Y 2S 1 States of 63CuS
Note. One standard deviation error on the last digits is quoted in parentheses.
Copyright © 1999 by Academic Press
330
O’BRIEN, DULICK, AND DAVIS
TABLE 2 Q 21 and Q 2 Bandhead Positions, Assignments, and Fit Residuals (cm 21) for the Y 2S 1–X 2P Transition of CuS
The fitting program incorporated Dunham-type vibronic energy expressions for the 2 S 1 and 2 P states, using massindependent constants (13) E v ~ 2 S 1 ! 5 T e 1 m 21/ 2 U 10 ~v 1 12 ! 1 m 21 U 20 ~v 1 12 ! 2 1 m 23/ 2 U 30 ~v 1 12 ! 3
[1]
E v ~ 2 P! 5 m 21/ 2 U 10 ~v 1 12 ! 1 m 21 U 20 ~v 1 12 ! 2 1 m 23/ 2 U 30 ~v 1 12 ! 3 7 12 A 7 12 a A ~v 1 12 ! [2] where the upper sign refers to the X 2 P 1/ 2 spin– orbit component and the lower sign refers to the X 2 P 3/ 2 spin– orbit component. The X 2 P state is known to be inverted, A 5 2433 cm 21 (1– 8). The Dunham-type mass-dependent molecular parameters for the X 2 P and Y 2 S 1 state of 63CuS are presented in Table 1. Bandhead positions, assignments, and fit residuals are presented in Table 2. There were no significant deviations from
the expected isotopic relationships among the molecular parameters for 63CuS and 65CuS. The observed ground state state molecular constants are in good agreement with the literature values (1– 8) (see Table 1). The observed excited state transition energy and vibrational constants are in reasonable agreement with the value predicted from ab initio calculations (11) (see Table 1). The ab initio calculations (11) also predict a shorter bond upon excitation to the Y 2 S 1 state, which agrees with our violet-degraded bandheads. ACKNOWLEDGMENTS Partial support for this work was provided by the National Science Foundation’s Professional Opportunities for Women in Research and Education Program through Grant NSF-CHE-9753254.
REFERENCES 1. M. Biron, C. R. Acad. Sci., Paris, B 258, 4228 – 4230 (1964). 2. M. Biron, C. R. Acad. Sci., Paris, B 274, 978 –980 (1972).
Copyright © 1999 by Academic Press
Y 2 S 1 —X 2 P TRANSITION OF CuS 3. M. Biron, C. R. Acad. Sci., Paris, B 281, 401– 403 (1975). 4. M. Biron, C. R. Acad. Sci., Paris, B 283, 209 –212 (1976). 5. F. David, M. Douay, and Y. Lefebvre, J. Mol. Spectrosc. 112, 115–126 (1985). 6. T. C. Steimle, W.-L. Chang, and D. F. Nachman, J. Chem. Phys. 89, 7172–7179 (1988). 7. Y. Lefebvre, J. M. Delaval, and J. Schamps, Phys. Scripta 44, 355–357 (1991). 8. F. David, J. M. Delaval, and Y. Lefebvre, Phys. Scripta 31, 570 –578 (1985).
331
9. Y. Lefebvre, B. Pinchemel, J. M. Delaval, and J. Schamps, Phys. Scripta 25, 329 –332 (1982). 10. L. C. O’Brien, R. L. Kubicek, S. J. Wall, D. E. Koch, R. J. Friend, and C. R. Brazier, J. Mol. Spectrosc. 180, 365–368 (1996). 11. S. R. Langhoff and C. W. Bauschlicher, Jr., Chem. Phys. Lett. 124, 241–247 (1986). 12. “Handbook of Chemistry and Physics,” 71st ed., CRC Press, Boston, MA, 1990. 13. P. F. Bernath, “Spectra of Atoms and Molecules,” Oxford University Press, New York, 1995.
Copyright © 1999 by Academic Press