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Emission spectroscopy of two new systems of TaO
Journal of Molecular Spectroscopy 221 (2003) 7–12 www.elsevier.com/locate/jms
Emission spectroscopy of two new systems of TaO R.S. Rama and P.F. Bernatha,b,* b
a Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA Department of Chemistry, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
Received 3 January 2003; in revised form 6 June 2003
Abstract The TaO molecule was inadvertently formed by exciting a mixture of TaCl5 vapor and He in a microwave discharge lamp, and the spectra from the near infrared to the near ultraviolet regions were recorded at high resolution using a Fourier transform spectrometer. Two new bands observed near 23 520 and 25 010 cm1 have been identified as 0–0 bands of two new electronic transitions. The lower state of these transitions is the same as the lower state of a transition near 10 000 cm1 recently seen by Al-Khalili et al. [J. Mol. Spectrosc. 198 (1999) 230]. A combined fit of the lines of the new transitions and those of the near infrared transition has provided an improved set of spectroscopic constants. The nature of the new electronic transitions is not clear and we have considered both the 2 D5=2 –2 P3=2 and the 4 P5=2 –4 R 3=2 possibilities. Ó 2003 Elsevier Inc. All rights reserved.
1. Introduction The spectra of TaO have been known for several decades and are relatively well characterized from gas phase [1–4] and matrix isolation [5–7] studies. The ground state of TaO has been established as a regular 2 D state arising from the r2 d configuration [4,5]. Weltner and McLeod [5] trapped the TaO and TaO2 molecules in neon and argon matrices after heating tantalum oxide to 2270 K, and they recorded absorption spectra from the near infrared to the near ultraviolet. They observed a large number of transitions having a common X 2 D3=2 lower state. This work was followed by an emission study of TaO by Cheetham and Barrow [4] who, in addition to the bands involving the X 2 D3=2 lower state, also observed a large number of transitions having a X 2 D5=2 lower state. They rotationally analyzed many bands and established that the X 2 D5=2 spin component lies at about 3505 cm1 above the X 2 D3=2 spin component. More recently the infrared spectra of tantalum oxides trapped in argon matrices have been re-investigated [6,7]. The spectra of TaO have also recently been re-investigated by Ram and Bernath [8] and by Al-Khalili et al. [9]. Ram and Bernath reported the analysis of several bands * Corresponding author. Fax: 1-519-746-0435. E-mail address: [email protected] (P.F. Bernath).
0022-2852/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0022-2852(03)00198-X
belonging to the H 2 P1=2 –X 2 D3=2 and K 2 U5=2 – X 2 D3=2 transitions, while Al-Khalili et al. [9] reported on the high resolution analysis of numerous bands involving 14 substates. In addition to transitions involving the X 2 D3=2 and X 2 D5=2 lower states, Al-Khalili et al. [9] observed new bands near 10 000 cm1 which have no link to the previously known ground or excited states of TaO. The bands near 10 000 cm1 were classified into two groups, System I and System II. The bands belonging to System I were free from hyperfine splitting, while the rotational structure of bands belonging to System II were blended because of considerable nuclear hyperfine structure. System II was tentatively assigned as a 2 P1=2 –2 R transition. There are a few theoretical studies of TaO focused on the ground X 2 D state and the low-lying 4 R state [10–12]. Rakowitz et al. [10,11] have calculated the spectroscopic properties of the low-lying 2 D and 4 R states using spinfree relativistic no-pair ab initio core model potentials while Dolg et al. [12] have predicted the spectroscopic properties of the same two states using the CASSCF + MRCI + SCC and CASSCF + ACPF calculations. Dolg et al. [12] predict that the 4 R state lies 0.76 eV above the ground state. Theoretical calculations for higher excited states are lacking. In this work we have observed two new transitions with 0–0 bands near 23 520 and 25 010 cm1 , which are free from hyperfine effects, and have the same lower
8
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
state as System I of Al-Khalili et al. [9]. For the sake of convenience, we have decided to label the common lower state as 12 P3=2 . The rotational analysis of these two bands will be reported in this paper.
2. Experimental The emission bands of TaO were produced during a search for TaCl bands in an electrodeless microwave discharge through a flowing mixture of TaCl5 vapor and He. The TaO bands were observed without adding any O2 to the mixture presumably as the result of reactions with impurities. The TaO bands were easily distinguished from those of TaCl by their characteristic larger spacing of the rotational lines. The discharge tube was made of quartz and had an outside diameter of 12 mm. The emission from the lamp was sent directly into the entrance aperture of the 1-m Fourier transform spectrometer associated with the McMath-Pierce Telescope of the National Solar Observatory. The spectrometer was equipped with a UV beam splitter and silicon photodiode detectors. The spectra were recorded in two parts: 9000–19 000 and 17 000–35 000 cm1 . For the 9000–19 000 cm1 region OG530 red pass filters were used and the spectra were recorded at 0.02 cm1 resolution by coadding six scans in 1 h of integration. The 17 000–35 000 cm1 region was recorded using a CuSO4 filter and coadding six scans at 0.03 cm1 resolution. The spectral line positions were extracted from the observed spectra using a data reduction program called PC-DECOMP. The peak positions were determined by fitting a Voigt line shape function to each spectral feature. The strongest TaO lines have typical widths of
0.045 cm1 and signal-to-noise ratios of 12:1. In our previous work [8] the TaO bands were observed in a hollow cathode lamp by discharging a mixture of Ne and a trace of N2 and the spectra were calibrated using the measurement of Ne atomic lines provided by Palmer and Engleman [13]. The present spectra were also calibrated using the measurements the Ne atomic lines [13] observed in our previous spectra by transferring the calibration using common TaO molecular lines in the two spectra. The uncertainty of measurements is expected to be of the order of 0.003 cm1 .
3. Results and discussion In addition to the bands observed by previous workers [4,8,9], two new bands were identified near 23 520 and 25 010 cm1 (see Fig. 1). These bands consist of R, P, and Q branches each split into two components at higher J values. The splitting occurs because of X-doubling. The rotational analysis of these bands indicates that they have the same lower state as the 0–0 band of System I of Al-Khalili et al. [9] observed near 10 026 cm1 . These authors have explored various assignments for the lower state including 2 R, 2 P1=2 , 2 P3=2 , and 2 D3=2 , without reaching a definite conclusion. Two likely possibilities were obtained by assuming that the excited state was a 2 R state and that the lower state was 2 P1=2 or 2 P3=2 . The analysis of our new transitions indicates that the excited states are free from X-doubling and the doubling in the P, Q, and R branches is mainly due to X-doubling in the lower state. No off-diagonal or other higher vibrational bands could be identified. Once the J assignment in the new bands was made by comparing their
Fig. 1. A portion of the 25 010 cm1 band of TaO.
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
lower state combination differences with those of System I of Al-Khalili et al. [9], an improved set of constants was obtained from a combined fit of the lines of both new transitions with the lines from the near infrared transition of Al-Khalili et al. [9]. The molecular constants were obtained in two different fits. In the first fit the lines were fitted using the following HundÕs case (c) empirical energy level expression: 2
3
Fv ðJ Þ ¼ Tv þ Bv J ðJ þ 1Þ Dv ½J ðJ þ 1Þ þ Hv ½J ðJ þ 1Þ 1=2½pv ðJ þ 1=2Þ þ pDv ðJ þ 1=2Þ 5
þ pHv ðJ þ 1=2Þ :
3
ð1Þ
The plus and minus signs in Eq. (1) refer to e and f parity levels, respectively, which have been chosen arbitrarily in the two new bands. The lines in the different bands were weighted depending upon the signal-to-noise ratio and extent of blending. The positions of rotational lines in the new transitions are provided in Table 1 and the derived HundÕs case (c) molecular constants are provided in Table 2. The constants of Table 2 indicate that the excited states of the 23 520 and 25 010 cm1 transitions are free from X-doubling suggesting that 2 D excited state spin components may be involved. The splitting in the higher J rotational lines of the two new bands arises entirely due to the presence of a small X-doubling in the lower state. The determination of small X-doubling constant pD [)6.9473 (56) 107 cm1 ] is consistent with the 2 P3=2 assignment for the lower state, suggesting that the excited states of the new transitions are 2 D5=2 spin components (see the discussion below, however). In the second fit the lines from the three bands were fitted using a HundÕs case (a) energy level expression. The constants obtained from this fit are provided in Table 3. In this fit the near infrared transition near 10 026 cm1 was treated as a 2 R–2 P3=2 subband while the two new transitions were treated as 2 D5=2 –2 P3=2 subbands. All spin–orbit coupling constants were arbitrarily set to 1000 cm1 . It can be noted that the excited state of the near infrared transition can be fitted as 2 P or 2 R states. The determination of substantial X-doubling [p ¼ 0:084849 cm1 , Table 2] and large spin splitting [c ¼ 0:856944 cm1 , Table 3] constants for this state in the case (c) and case (a) fits, respectively, are consistent with X ¼ 1=2 assignment for this state. Based on the work of Kopp and Hougen [14], these values are more consistent with a 2 P1=2 state than a 2 R1=2 state. The near infrared transition is then primarily a forbidden 2 P1=2 –2 P3=2 transition. A comparison of the excited state rotational constants (Table 2) obtained in the present work with the constants available for the other excited states reported previously [4,8,9] indicates that the present rotational constants (B0 ¼ 0:3838151ð39Þ cm1 , D0 ¼ 2:7863 ð41Þ 107 cm1 ) for the 25 010 cm1 band agree very well with the constants (B0 ¼ 0:38393 cm1 , D0 ¼ 2:89 107 cm1 )
9
for the R state [4], except for D0 , which was a misprint and was corrected later [15]. Seeing this coincidence, it is tempting to conclude that R state is the excited state of the 25 010 cm1 transition. But this assignment is ruled out since the R state is a 2 D3=2 spin component whereas the excited state of the 25 010 cm1 band is a 2 D5=2 spin component. Also a small perturbation was observed by Cheetham and Barrow [4] at J ¼ 22:5 in the R state whereas our spectrum is free of perturbations. The assignment of the two new transitions as 2 D5=2 –2 P3=2 is only tentative. The new transitions are very likely X ¼ 5=2–X ¼ 3=2 transitions because the Xdoubling in the lower state is small and has a cubic dependence on J. The upper states have no observable X-doubling and the transitions have a strong Q branch. A very attractive possibility is that the new transitions are both 4 P5=2 –4 R 3=2 . This means that the 1-lm transition of Al-Khalili et al. [9] is then 4 P1=2 –4 R 3=2 . All of these transitions are allowed by HundÕs case (a) selection rules (e.g., DR ¼ 0) and the states have the expected Xdoubling behavior. Clearly more work is necessary to confirm this suggestion. Al-Khalili et al. [9] also considered the possibility that Systems I and II are two spin-components of a HundÕs case (a) 4 P–4 R transition. In this case, System I would be the 4 P1=2 –4 R 3=2 spin-component and System II would be the 4 P1=2 –4 R 1=2 spin-component. Note that for a HundÕs case (a) 4 P–4 R transition the allowed sub4 4 4 4 bands are 4 P5=2 –4 R 3=2 , P1=2 – R3=2 , P3=2 – R1=2 , and 4 P1=2 –4 R1=2 . The small hyperfine splitting in System I and the large hyperfine structure in System II as well as the X-doubling support this assignment. In the end, however, no satisfactory combined fit was obtained and Al-Khalili et al. [9] preferred to assign each system as a doublet. However, System II was very dense and no convincing rotational assignment could be made because of fragmentary branches. We prefer the quartet assignment for the 1 micron bands and for the two new transitions, but can offer no proof so we have retained the doublet labels. We are unable to determine the vibrational intervals or the equilibrium constants due to the lack of higher vibrational or off-diagonal bands associated with the new transitions. The case (c) rotational constants of B0 ¼ 0:3809991ð39Þ cm1 and B0 ¼ 0:3838890ð40Þ cm1 for the excited states of the 23 520 and 25 010 cm1 transitions provide the bond lengths of r0 ¼ 1:7351564ð97Þ and , respectively, while the rotational r0 ¼ 1:7286130ð97Þ A constant of B0 ¼ 0:3960362ð38Þ cm1 for the common 12 P3=2 lower state provides the bond length of for this state. It is surprising to note r0 ¼ 1:7018963ð79Þ A that there are no ab initio calculations on the numerous excited states in spite of considerable interest in the spectroscopy of TaO over the past few decades. A high level ab initio calculation for the excited states would be most welcome in order to account for the observed
10
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
Table 1 Observed line positions (in cm1 ) for the new transitions of TaO J
Ree(J)
O)C
Pee(J)
D5=2 –12 P3=2 0–0 (23 520 cm1 ) 8.5 9.5 10.5 23526.634 )13 11.5 23527.067 5 12.5 23527.442 )5 23507.650 13.5 23527.798 )5 23506.480 14.5 23528.126 )2 23505.282 15.5 23528.423 1 23504.061 16.5 23528.685 )1 23502.793 17.5 23528.917 )4 23501.500 18.5 23529.119 )7 23500.185 19.5 23529.296 )3 23498.838 20.5 23529.442 )0 23497.449 21.5 23529.554 )2 23496.044 22.5 23494.609 23.5 23493.127 24.5 23491.645 25.5 23490.120 26.5 23488.557 27.5 23486.964 28.5 23529.480 )16 23485.348 29.5 23529.357 )10 23483.701 30.5 23529.204 )2 23482.016 31.5 23529.014 )0 23480.318 32.5 23528.789 )3 23478.575 33.5 23528.540 0 23476.801 34.5 23528.259 2 23475.014 35.5 23527.940 )3 23473.189 36.5 23527.604 5 23471.334 37.5 23527.227 4 23469.436 38.5 23526.813 )4 23467.520 39.5 23526.374 )7 23465.574 40.5 23525.913 )1 41.5 23525.426 11 23461.586 40.5 23459.531 43.5 23524.339 14 23457.464 44.5 23523.743 8 23455.367 45.5 23523.101 )11 23453.229 46.5 23522.470 10 23451.068 47.5 23521.779 4 23448.889 48.5 23521.056 )4 23446.661 49.5 23520.320 7 23444.405 50.5 23442.126 51.5 23439.828 52.5 23437.469 53.5 23435.071 54.5 23432.683 55.5 23430.262 56.5 23427.767 57.5 23425.269 58.5 23422.740 59.5 60.5 61.5 62.5 63.5
O)C
Rff(J)
O)C
Pff(J)
O)C
Qef(J)
O)C
Qfe(J)
O)C
2
2 D5=2 –12 P3=2 0–0 (25 010 cm1 ) 10.5 11.5 12.5 13.5 25018.943 )13
10 7 7 13 3 )3 0 1 )11 )9 )6 )20 )4 )1 )6 )12 )10 )8 )15 )4 )9 )15 )3 1 6 )3 0 4 7 )8 )4 0 )5 )5 9 3 1 6 22 8 )14 4 20 )8 )8 )8
23526.634 23527.067 23527.442 23527.798 23528.126 23528.423 23528.685 23528.917 23529.119 23529.296 23529.442 23529.554
)12 6 )3 )3 0 4 2 0 )2 2 6 6
23529.480 23529.357 23529.192 23528.994 23528.768 23528.510 23528.230 23527.908 23527.563 23527.183 23526.773 23526.335 23525.854 23525.357 23524.825 23524.269 23523.664 23523.046 23522.397 23521.709 23520.987 23520.246 23519.459
1 9 7 2 1 )3 3 )3 )0 )2 )4 )1 )11 )7 )5 3 )8 1 10 11 9 19 16
23507.650 23506.480 23505.282 23504.061 23502.793 23501.500 23500.185 23498.838 23497.449 23496.044 23494.609 23493.127 23491.645 23490.120 23488.557 23486.964 23485.348 23483.701 23482.016 23480.318 23478.575 23476.801 23474.982 23473.163 23471.298 23469.399 23467.483 23465.522 23463.543 23461.521 23459.480 23457.406 23455.307 23453.169 23450.994 23448.811 23446.569 23444.319 23442.037 23439.702 23437.372 23434.984 23432.558 23430.124 23427.640
12 9 9 16 6 1 5 6 )4 )1 2 )11 7 11 7 3 7 10 6 19 16 13 )5 8 4 )2 5 )4 1 )7 )4 )3 4 2 )6 8 )6 2 9 )6 14 8 )5 4 )6
23518.484 23518.196 23517.883 23517.534 23517.168 23516.757 23516.330 23515.849 23515.356 23514.829 23514.272 23513.687 23513.068 23512.420 23511.744 23511.034 23510.295 23509.526 23508.729 23507.898 23507.039 23506.145 23505.219 23504.264 23503.282 23502.270
)2 )4 )1 )4 6 1 11 )3 1 2 2 4 4 4 6 5 5 5 8 7 9 6 0 )3 )2 )1
23518.484 )2 23518.196 )4 23517.883 )2 23517.534 )5 23517.168 5 23516.757 )0 23516.33 9 23515.849 )6 23515.356 )2 23514.829 )2 23514.272 )3 23513.687 )1 23513.068 )3 23512.42 )3 23511.744 )2 23511.034 )5 23510.295 )6 23509.526 )7 23508.729 )6 23507.898 )8 23507.039 )8 23506.145 )13 23505.24 1 23504.285 )4 23503.309 )0 23502.304 5
23500.157 23499.050 23497.913 23496.751 23495.545 23494.324 23493.067 23491.775 23490.461 23489.100 23487.726 23486.316 23484.877 23483.397 23481.893
3 0 )1 2 )8 )2 )1 )4 1 )9 )3 )0 3 )3 )2
23478.793 23477.199 23475.562 23473.891 23472.211 23470.492 23468.729 23466.941 23465.147 23463.280 23461.407
1 5 )3 )13 )1 3 )7 )8 15 )3 4
23500.187 0 23499.083 )1 23497.95 )3 23496.79 )1 23495.596 )1 23494.378 4 23493.127 7 23491.835 0 23490.524 5 23489.172 )1 23487.796 )0 23486.389 )0 23484.947 )4 23483.481 )0 23481.98 )2 23480.447 )4 23478.89 0 23477.302 4 23475.669 )5 23474.031 11 23472.329 )6 23470.614 )4 23468.879 8 23467.098 6 23465.288 6 23463.431 )10 23461.576 8 23459.66 )5 23457.729 )0
25008.736 25008.453 25008.151 25007.822
0 )4 )2 )3
25008.736 25008.453 25008.151 25007.822
)1 )5 )3 )4
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
11
Table 1 (continued) J
Ree(J)
O)C
14.5 15.5 16.5 17.5 18.5 19.5 20.5 21.5 22.5 23.5 24.5 25.5 26.5 27.5 28.5 29.5 30.5 31.5 32.5 33.5 34.5 35.5 36.5 37.5 38.5 39.5 40.5 41.5 42.5 43.5 44.5 45.5 46.5 47.5 48.5 49.5 50.5 51.5 52.5 53.5 54.5 55.5 56.5 57.5 58.5 59.5 60.5 61.5 62.5 63.5 64.5
25019.367 25019.755 25020.119 25020.473 25020.781 25021.081 25021.345 25021.581 25021.799 25021.995 25022.164 25022.322 25022.440 25022.540 25022.609 25022.655
)4 )6 )7 5 )5 4 )1 )9 )9 )9 )10 2 )0 3 1 )1
25021.029
6
25020.412 25020.050 25019.669 25019.283 25018.844 25018.392 25017.936 25017.439
12 )1 )8 5 )9 )13 6 7
25016.356 25015.784 25015.172 25014.549 25013.913 25013.233 25012.531 25011.805
)1 2 )10 )9 6 3 2 3
Pee(J)
O)C
24995.192 24994.028 24992.834 24991.625 24990.385 24989.123 24987.833 24986.518 24985.180 24983.818 24982.433 24981.004 24979.583 24978.129 24976.643 24975.139 24973.603 24972.056 24970.476 24968.877 24967.248 24965.605 24963.926 24962.215 24960.493 24958.747 24956.974 24955.177 24953.335 24951.514 24949.635
)9 )5 )7 )0 1 3 2 0 )1 )2 )1 )20 )7 )3 )7 )4 )10 )1 )1 3 2 11 8 )3 0 4 4 5 )15 10 2
24945.821 24943.869 24941.896 24939.903 24937.905 24935.847
2 )6 )10 )11 8 )9
24929.573 24927.455
)11 10
Rff(J) 25019.367 25019.755 25020.119 25020.473 25020.781 25021.081 25021.345 25021.581 25021.799 25021.995 25022.164 25022.302 25022.422 25022.523 25022.596 25022.635
25021.930 25021.723 25021.497 25021.238 25020.971 25020.642 25020.335 25019.979 25019.601 25019.196 25018.783 25018.313 25017.836 25017.344 25016.806 25016.250 25015.643 25015.059 25014.434 25013.759
O)C )1 )3 )4 9 0 9 6 )1 )1 1 1 )5 )4 2 4 )2
)0 )4 )2 )8 3 )23 )2 )4 )4 )5 11 )5 )2 11 3 2 )24 )1 5 )12
Pff(J)
O)C
24995.192 24994.028 24992.834 24991.625 24990.385 24989.123 24987.833 24986.518 24985.180 24983.818 24982.433 24981.004 24979.583 24978.129 24976.643 24975.139 24973.603 24972.019 24970.450 24968.840 24967.211 24965.552 24963.878 24962.183 24960.447 24958.690 24956.922 24955.114 24953.291 24951.450 24949.570 24947.678 24945.742 24943.799
)7 )2 )3 5 6 10 9 9 9 9 11 )7 8 14 12 16 13 )13 )1 )4 )3 )7 )2 7 )1 )5 4 )3 0 9 5 12 )0 6
24939.819 24937.791 24935.750 24933.668 24931.582 24929.462
)3 )8 )2 )13 )2 )1
Qef(J)
O)C
Qfe(J)
O)C
25007.468 25007.094 25006.699 25006.274 25005.822 25005.349 25004.854 25004.326 25003.775 25003.213 25002.614 25001.993 25001.344 25000.669 24999.980 24999.257 24998.517
)4 )0 6 7 5 6 10 6 3 13 12 12 9 3 9 5 9
25007.468 25007.094 25006.699 25006.274 25005.822 25005.349 25004.854 25004.326 25003.775 25003.213 25002.614 25001.993 25001.344 25000.679 24999.993 24999.268 24998.531
)6 )3 2 3 0 1 4 )1 )5 4 1 )1 )5 )2 5 )2 2
24996.132 24995.298 24994.430 24993.534 24992.613 24991.667 24990.707 24989.718 24988.703 24987.659 24986.596 24985.506 24984.391 24983.252 24982.090 24980.899 24979.688 24978.446 24977.188 24975.901 24974.585 24973.250 24971.883 24970.484 24969.086 24967.639 24966.178 24964.687 24963.168 24961.635 24960.059
3 11 10 5 0 )5 0 1 2 )2 )2 )2 )3 )3 )1 )4 )1 )5 1 3 )0 3 0 )10 6 )2 2 0 )4 4 )7
24996.155 24995.320 24994.446 24993.559 24992.649 24991.705 24990.753 24989.763 24988.756 24987.719 24986.657 24985.573 24984.461 24983.332 24982.173 24980.984 24979.780 24978.546 24977.281 24976.002 24974.698 24973.360 24972.016 24970.631 24969.211 24967.782 24966.330
)2 3 )6 )5 )2 )7 3 )1 3 2 1 1 )0 5 4 )1 4 3 )3 )0 4 )2 11 8 )5 )2 3
24963.330 24961.809 24960.250 24958.674
)8 4 1 7
Note. O)C are observed minus calculated line positions in units of 103 cm1 .
electronic states and also to predict new transitions that have not yet been observed.
4. Summary The spectrum of TaO has been observed using a microwave discharge of a mixture of TaCl5 and He and the
spectra in the 3000–35 000 cm1 region were recorded at high resolution using a Fourier transform spectrometer. Two new bands observed at 23 520 and 25 010 cm1 have been tentatively assigned as the 0–0 bands of two new 2 D5=2 –2 P3=2 transitions with lower state in common with System I of Al-Khalili et al. [9]. Improved sets of spectroscopic constants have been observed from a combined fit of the lines of the new transitions and the
12
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
Table 2 HundÕs case (c) molecular constants (in cm1 ) for TaO Constantsa T00 B0 107 D0 1013 H0 102 p0 106 pD0 1011 pH 0 ) R0 (A
12 P3=2 0.0b 0.3960362(38) 2.6361(31) 3.430(83)
2
R1=2 (10 025 cm1 )
2
10025.90046(78) 0.3860478(37) 2.6161(27)
23519.70056(75) 0.3809991(39) 2.9044(42)
—
8.4849(33) )1.441(12) 5.775(96) 1.7237729(82)
—
)0.69473(89) —
1.7018963(79)
D5=2 (23 520 cm1 )
2
D5=2 (25 010 cm1 )
25010.20367(81) 0.3838890(40) 2.7976(42)
—
—
—
—
—
—
—
—
1.7351564(97)
1.7286130(97)
a
Numbers in parentheses are one standard deviation in the last two digits quoted. b Fixed value, see text for details.
Table 3 HundÕs case (a) molecular constants (in cm1 ) for TaO R1=2 (10 025 cm1 )
Constantsa
12 P3=2
2
T00 A0 B0 107 D0 1013 H0 104 q0 c0 106 cD0 1011 cH 0 ) R0 (A
0.0b 1000.0c 0.3958795(37) 2.6342(31) 3.416(82) 8.895(11)
10525.93535(77)
— — —
1.7022333(80)
2
D5=2 (23 520 cm1 )
23020.07039(74) 1000.0c 0.3809262(39) 2.9031(41)
—
0.3860461(37) 2.6159(27)
2
D5=2 (25 010 cm1 )
24510.57855(81) 1000.0c 0.3838151(39) 2.7963(41)
—
—
—
—
—
—
—
—
—
—
—
0.856944(34) )2.492(12) 5.818(95) 1.7237767(88)
1.7353224(89)
—
1.7287794(88)
a
Numbers in parentheses are one standard deviation in the last two digits quoted. b Fixed value. c Fixed value, see text for details.
near infrared transition, and a 2 P1=2 assignment is proposed for the excited state of the near infrared transition. Alternatively, our new transitions could be 4 P5=2 –4 R 3=2 transitions and then the excited state of the near infrared transition would be 4 P1=2 . More theoretical work is needed to distinguish between these possibilities and, in particular, to locate the quartet transitions.
Acknowledgments We thank M. Dulick and D. Bransden of the National Solar Observatory for assistance in obtaining the spectra. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation. The research described here was supported by funding from NASA laboratory astrophysics program. Some support was also provide by the Natural Sciences and Engineering Research Council of Canada.
References [1] [2] [3] [4] [5] [6] [7] [8] [9] [10] [11] [12] [13] [14] [15]
C.C. Kiess, E.Z. Stowall, Bur. Standards J. Res. 12 (1934) 459–469. D. Premaswarup, Indian J. Phys. 29 (1955) 109–120. D. Premaswarup, R.F. Barrow, Nature 180 (1957) 602. C.J. Cheetham, R.F. Barrow, Trans. Faraday Soc. 63 (1967) 1835–1845. W. Weltner Jr., D. McLeod Jr., J. Chem. Phys. 42 (1965) 882–891. M. Zhou, L. Andrews, J. Phys. Chem. A 102 (1998) 8251–8260. M. Chen, X. Wang, L. Zhang, M. Yu, Q. Qin, Chem. Phys. 242 (1999) 81–90. R.S. Ram, P.F. Bernath, J. Mol. Spectrosc. 191 (1998) 125–136. A. Al-Khalili, U. H€allsten, O. Launila, J. Mol. Spectrosc. 198 (1999) 230–238. F. Rakowitz, C.M. Marian, L. Seijo, U. Wahlgren, J. Chem. Phys. 110 (1999) 3678–3686. F. Rakowitz, C.M. Marian, L. Seijo, U. Wahlgren, J. Chem. Phys. 111 (1999) 10436–10443. M. Dolg, H. Stoll, H. Preuss, R.M. Pitzer, J. Phys. Chem. 97 (1993) 5852–5859. B.A. Palmer, R. Engleman, Atlas of the Thorium Spectrum, Los Alamos National Laboratory, Los Alamos, NM, 1993. I. Kopp, J.T. Hougen, Can. J. Phys. 45 (1967) 2581–2596. K.P. Huber, G. Herzberg, Molecular Spectra and Molecular Structure, IV. Constants of Diatomic Molecules, Van Nostrand Reinhold, New York, 1979.
Emission spectroscopy of two new systems of TaO R.S. Rama and P.F. Bernatha,b,* b
a Department of Chemistry, University of Arizona, Tucson, AZ 85721, USA Department of Chemistry, University of Waterloo, Waterloo, Ont., Canada N2L 3G1
Received 3 January 2003; in revised form 6 June 2003
Abstract The TaO molecule was inadvertently formed by exciting a mixture of TaCl5 vapor and He in a microwave discharge lamp, and the spectra from the near infrared to the near ultraviolet regions were recorded at high resolution using a Fourier transform spectrometer. Two new bands observed near 23 520 and 25 010 cm1 have been identified as 0–0 bands of two new electronic transitions. The lower state of these transitions is the same as the lower state of a transition near 10 000 cm1 recently seen by Al-Khalili et al. [J. Mol. Spectrosc. 198 (1999) 230]. A combined fit of the lines of the new transitions and those of the near infrared transition has provided an improved set of spectroscopic constants. The nature of the new electronic transitions is not clear and we have considered both the 2 D5=2 –2 P3=2 and the 4 P5=2 –4 R 3=2 possibilities. Ó 2003 Elsevier Inc. All rights reserved.
1. Introduction The spectra of TaO have been known for several decades and are relatively well characterized from gas phase [1–4] and matrix isolation [5–7] studies. The ground state of TaO has been established as a regular 2 D state arising from the r2 d configuration [4,5]. Weltner and McLeod [5] trapped the TaO and TaO2 molecules in neon and argon matrices after heating tantalum oxide to 2270 K, and they recorded absorption spectra from the near infrared to the near ultraviolet. They observed a large number of transitions having a common X 2 D3=2 lower state. This work was followed by an emission study of TaO by Cheetham and Barrow [4] who, in addition to the bands involving the X 2 D3=2 lower state, also observed a large number of transitions having a X 2 D5=2 lower state. They rotationally analyzed many bands and established that the X 2 D5=2 spin component lies at about 3505 cm1 above the X 2 D3=2 spin component. More recently the infrared spectra of tantalum oxides trapped in argon matrices have been re-investigated [6,7]. The spectra of TaO have also recently been re-investigated by Ram and Bernath [8] and by Al-Khalili et al. [9]. Ram and Bernath reported the analysis of several bands * Corresponding author. Fax: 1-519-746-0435. E-mail address: [email protected] (P.F. Bernath).
0022-2852/$ - see front matter Ó 2003 Elsevier Inc. All rights reserved. doi:10.1016/S0022-2852(03)00198-X
belonging to the H 2 P1=2 –X 2 D3=2 and K 2 U5=2 – X 2 D3=2 transitions, while Al-Khalili et al. [9] reported on the high resolution analysis of numerous bands involving 14 substates. In addition to transitions involving the X 2 D3=2 and X 2 D5=2 lower states, Al-Khalili et al. [9] observed new bands near 10 000 cm1 which have no link to the previously known ground or excited states of TaO. The bands near 10 000 cm1 were classified into two groups, System I and System II. The bands belonging to System I were free from hyperfine splitting, while the rotational structure of bands belonging to System II were blended because of considerable nuclear hyperfine structure. System II was tentatively assigned as a 2 P1=2 –2 R transition. There are a few theoretical studies of TaO focused on the ground X 2 D state and the low-lying 4 R state [10–12]. Rakowitz et al. [10,11] have calculated the spectroscopic properties of the low-lying 2 D and 4 R states using spinfree relativistic no-pair ab initio core model potentials while Dolg et al. [12] have predicted the spectroscopic properties of the same two states using the CASSCF + MRCI + SCC and CASSCF + ACPF calculations. Dolg et al. [12] predict that the 4 R state lies 0.76 eV above the ground state. Theoretical calculations for higher excited states are lacking. In this work we have observed two new transitions with 0–0 bands near 23 520 and 25 010 cm1 , which are free from hyperfine effects, and have the same lower
8
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
state as System I of Al-Khalili et al. [9]. For the sake of convenience, we have decided to label the common lower state as 12 P3=2 . The rotational analysis of these two bands will be reported in this paper.
2. Experimental The emission bands of TaO were produced during a search for TaCl bands in an electrodeless microwave discharge through a flowing mixture of TaCl5 vapor and He. The TaO bands were observed without adding any O2 to the mixture presumably as the result of reactions with impurities. The TaO bands were easily distinguished from those of TaCl by their characteristic larger spacing of the rotational lines. The discharge tube was made of quartz and had an outside diameter of 12 mm. The emission from the lamp was sent directly into the entrance aperture of the 1-m Fourier transform spectrometer associated with the McMath-Pierce Telescope of the National Solar Observatory. The spectrometer was equipped with a UV beam splitter and silicon photodiode detectors. The spectra were recorded in two parts: 9000–19 000 and 17 000–35 000 cm1 . For the 9000–19 000 cm1 region OG530 red pass filters were used and the spectra were recorded at 0.02 cm1 resolution by coadding six scans in 1 h of integration. The 17 000–35 000 cm1 region was recorded using a CuSO4 filter and coadding six scans at 0.03 cm1 resolution. The spectral line positions were extracted from the observed spectra using a data reduction program called PC-DECOMP. The peak positions were determined by fitting a Voigt line shape function to each spectral feature. The strongest TaO lines have typical widths of
0.045 cm1 and signal-to-noise ratios of 12:1. In our previous work [8] the TaO bands were observed in a hollow cathode lamp by discharging a mixture of Ne and a trace of N2 and the spectra were calibrated using the measurement of Ne atomic lines provided by Palmer and Engleman [13]. The present spectra were also calibrated using the measurements the Ne atomic lines [13] observed in our previous spectra by transferring the calibration using common TaO molecular lines in the two spectra. The uncertainty of measurements is expected to be of the order of 0.003 cm1 .
3. Results and discussion In addition to the bands observed by previous workers [4,8,9], two new bands were identified near 23 520 and 25 010 cm1 (see Fig. 1). These bands consist of R, P, and Q branches each split into two components at higher J values. The splitting occurs because of X-doubling. The rotational analysis of these bands indicates that they have the same lower state as the 0–0 band of System I of Al-Khalili et al. [9] observed near 10 026 cm1 . These authors have explored various assignments for the lower state including 2 R, 2 P1=2 , 2 P3=2 , and 2 D3=2 , without reaching a definite conclusion. Two likely possibilities were obtained by assuming that the excited state was a 2 R state and that the lower state was 2 P1=2 or 2 P3=2 . The analysis of our new transitions indicates that the excited states are free from X-doubling and the doubling in the P, Q, and R branches is mainly due to X-doubling in the lower state. No off-diagonal or other higher vibrational bands could be identified. Once the J assignment in the new bands was made by comparing their
Fig. 1. A portion of the 25 010 cm1 band of TaO.
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
lower state combination differences with those of System I of Al-Khalili et al. [9], an improved set of constants was obtained from a combined fit of the lines of both new transitions with the lines from the near infrared transition of Al-Khalili et al. [9]. The molecular constants were obtained in two different fits. In the first fit the lines were fitted using the following HundÕs case (c) empirical energy level expression: 2
3
Fv ðJ Þ ¼ Tv þ Bv J ðJ þ 1Þ Dv ½J ðJ þ 1Þ þ Hv ½J ðJ þ 1Þ 1=2½pv ðJ þ 1=2Þ þ pDv ðJ þ 1=2Þ 5
þ pHv ðJ þ 1=2Þ :
3
ð1Þ
The plus and minus signs in Eq. (1) refer to e and f parity levels, respectively, which have been chosen arbitrarily in the two new bands. The lines in the different bands were weighted depending upon the signal-to-noise ratio and extent of blending. The positions of rotational lines in the new transitions are provided in Table 1 and the derived HundÕs case (c) molecular constants are provided in Table 2. The constants of Table 2 indicate that the excited states of the 23 520 and 25 010 cm1 transitions are free from X-doubling suggesting that 2 D excited state spin components may be involved. The splitting in the higher J rotational lines of the two new bands arises entirely due to the presence of a small X-doubling in the lower state. The determination of small X-doubling constant pD [)6.9473 (56) 107 cm1 ] is consistent with the 2 P3=2 assignment for the lower state, suggesting that the excited states of the new transitions are 2 D5=2 spin components (see the discussion below, however). In the second fit the lines from the three bands were fitted using a HundÕs case (a) energy level expression. The constants obtained from this fit are provided in Table 3. In this fit the near infrared transition near 10 026 cm1 was treated as a 2 R–2 P3=2 subband while the two new transitions were treated as 2 D5=2 –2 P3=2 subbands. All spin–orbit coupling constants were arbitrarily set to 1000 cm1 . It can be noted that the excited state of the near infrared transition can be fitted as 2 P or 2 R states. The determination of substantial X-doubling [p ¼ 0:084849 cm1 , Table 2] and large spin splitting [c ¼ 0:856944 cm1 , Table 3] constants for this state in the case (c) and case (a) fits, respectively, are consistent with X ¼ 1=2 assignment for this state. Based on the work of Kopp and Hougen [14], these values are more consistent with a 2 P1=2 state than a 2 R1=2 state. The near infrared transition is then primarily a forbidden 2 P1=2 –2 P3=2 transition. A comparison of the excited state rotational constants (Table 2) obtained in the present work with the constants available for the other excited states reported previously [4,8,9] indicates that the present rotational constants (B0 ¼ 0:3838151ð39Þ cm1 , D0 ¼ 2:7863 ð41Þ 107 cm1 ) for the 25 010 cm1 band agree very well with the constants (B0 ¼ 0:38393 cm1 , D0 ¼ 2:89 107 cm1 )
9
for the R state [4], except for D0 , which was a misprint and was corrected later [15]. Seeing this coincidence, it is tempting to conclude that R state is the excited state of the 25 010 cm1 transition. But this assignment is ruled out since the R state is a 2 D3=2 spin component whereas the excited state of the 25 010 cm1 band is a 2 D5=2 spin component. Also a small perturbation was observed by Cheetham and Barrow [4] at J ¼ 22:5 in the R state whereas our spectrum is free of perturbations. The assignment of the two new transitions as 2 D5=2 –2 P3=2 is only tentative. The new transitions are very likely X ¼ 5=2–X ¼ 3=2 transitions because the Xdoubling in the lower state is small and has a cubic dependence on J. The upper states have no observable X-doubling and the transitions have a strong Q branch. A very attractive possibility is that the new transitions are both 4 P5=2 –4 R 3=2 . This means that the 1-lm transition of Al-Khalili et al. [9] is then 4 P1=2 –4 R 3=2 . All of these transitions are allowed by HundÕs case (a) selection rules (e.g., DR ¼ 0) and the states have the expected Xdoubling behavior. Clearly more work is necessary to confirm this suggestion. Al-Khalili et al. [9] also considered the possibility that Systems I and II are two spin-components of a HundÕs case (a) 4 P–4 R transition. In this case, System I would be the 4 P1=2 –4 R 3=2 spin-component and System II would be the 4 P1=2 –4 R 1=2 spin-component. Note that for a HundÕs case (a) 4 P–4 R transition the allowed sub4 4 4 4 bands are 4 P5=2 –4 R 3=2 , P1=2 – R3=2 , P3=2 – R1=2 , and 4 P1=2 –4 R1=2 . The small hyperfine splitting in System I and the large hyperfine structure in System II as well as the X-doubling support this assignment. In the end, however, no satisfactory combined fit was obtained and Al-Khalili et al. [9] preferred to assign each system as a doublet. However, System II was very dense and no convincing rotational assignment could be made because of fragmentary branches. We prefer the quartet assignment for the 1 micron bands and for the two new transitions, but can offer no proof so we have retained the doublet labels. We are unable to determine the vibrational intervals or the equilibrium constants due to the lack of higher vibrational or off-diagonal bands associated with the new transitions. The case (c) rotational constants of B0 ¼ 0:3809991ð39Þ cm1 and B0 ¼ 0:3838890ð40Þ cm1 for the excited states of the 23 520 and 25 010 cm1 transitions provide the bond lengths of r0 ¼ 1:7351564ð97Þ and , respectively, while the rotational r0 ¼ 1:7286130ð97Þ A constant of B0 ¼ 0:3960362ð38Þ cm1 for the common 12 P3=2 lower state provides the bond length of for this state. It is surprising to note r0 ¼ 1:7018963ð79Þ A that there are no ab initio calculations on the numerous excited states in spite of considerable interest in the spectroscopy of TaO over the past few decades. A high level ab initio calculation for the excited states would be most welcome in order to account for the observed
10
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
Table 1 Observed line positions (in cm1 ) for the new transitions of TaO J
Ree(J)
O)C
Pee(J)
D5=2 –12 P3=2 0–0 (23 520 cm1 ) 8.5 9.5 10.5 23526.634 )13 11.5 23527.067 5 12.5 23527.442 )5 23507.650 13.5 23527.798 )5 23506.480 14.5 23528.126 )2 23505.282 15.5 23528.423 1 23504.061 16.5 23528.685 )1 23502.793 17.5 23528.917 )4 23501.500 18.5 23529.119 )7 23500.185 19.5 23529.296 )3 23498.838 20.5 23529.442 )0 23497.449 21.5 23529.554 )2 23496.044 22.5 23494.609 23.5 23493.127 24.5 23491.645 25.5 23490.120 26.5 23488.557 27.5 23486.964 28.5 23529.480 )16 23485.348 29.5 23529.357 )10 23483.701 30.5 23529.204 )2 23482.016 31.5 23529.014 )0 23480.318 32.5 23528.789 )3 23478.575 33.5 23528.540 0 23476.801 34.5 23528.259 2 23475.014 35.5 23527.940 )3 23473.189 36.5 23527.604 5 23471.334 37.5 23527.227 4 23469.436 38.5 23526.813 )4 23467.520 39.5 23526.374 )7 23465.574 40.5 23525.913 )1 41.5 23525.426 11 23461.586 40.5 23459.531 43.5 23524.339 14 23457.464 44.5 23523.743 8 23455.367 45.5 23523.101 )11 23453.229 46.5 23522.470 10 23451.068 47.5 23521.779 4 23448.889 48.5 23521.056 )4 23446.661 49.5 23520.320 7 23444.405 50.5 23442.126 51.5 23439.828 52.5 23437.469 53.5 23435.071 54.5 23432.683 55.5 23430.262 56.5 23427.767 57.5 23425.269 58.5 23422.740 59.5 60.5 61.5 62.5 63.5
O)C
Rff(J)
O)C
Pff(J)
O)C
Qef(J)
O)C
Qfe(J)
O)C
2
2 D5=2 –12 P3=2 0–0 (25 010 cm1 ) 10.5 11.5 12.5 13.5 25018.943 )13
10 7 7 13 3 )3 0 1 )11 )9 )6 )20 )4 )1 )6 )12 )10 )8 )15 )4 )9 )15 )3 1 6 )3 0 4 7 )8 )4 0 )5 )5 9 3 1 6 22 8 )14 4 20 )8 )8 )8
23526.634 23527.067 23527.442 23527.798 23528.126 23528.423 23528.685 23528.917 23529.119 23529.296 23529.442 23529.554
)12 6 )3 )3 0 4 2 0 )2 2 6 6
23529.480 23529.357 23529.192 23528.994 23528.768 23528.510 23528.230 23527.908 23527.563 23527.183 23526.773 23526.335 23525.854 23525.357 23524.825 23524.269 23523.664 23523.046 23522.397 23521.709 23520.987 23520.246 23519.459
1 9 7 2 1 )3 3 )3 )0 )2 )4 )1 )11 )7 )5 3 )8 1 10 11 9 19 16
23507.650 23506.480 23505.282 23504.061 23502.793 23501.500 23500.185 23498.838 23497.449 23496.044 23494.609 23493.127 23491.645 23490.120 23488.557 23486.964 23485.348 23483.701 23482.016 23480.318 23478.575 23476.801 23474.982 23473.163 23471.298 23469.399 23467.483 23465.522 23463.543 23461.521 23459.480 23457.406 23455.307 23453.169 23450.994 23448.811 23446.569 23444.319 23442.037 23439.702 23437.372 23434.984 23432.558 23430.124 23427.640
12 9 9 16 6 1 5 6 )4 )1 2 )11 7 11 7 3 7 10 6 19 16 13 )5 8 4 )2 5 )4 1 )7 )4 )3 4 2 )6 8 )6 2 9 )6 14 8 )5 4 )6
23518.484 23518.196 23517.883 23517.534 23517.168 23516.757 23516.330 23515.849 23515.356 23514.829 23514.272 23513.687 23513.068 23512.420 23511.744 23511.034 23510.295 23509.526 23508.729 23507.898 23507.039 23506.145 23505.219 23504.264 23503.282 23502.270
)2 )4 )1 )4 6 1 11 )3 1 2 2 4 4 4 6 5 5 5 8 7 9 6 0 )3 )2 )1
23518.484 )2 23518.196 )4 23517.883 )2 23517.534 )5 23517.168 5 23516.757 )0 23516.33 9 23515.849 )6 23515.356 )2 23514.829 )2 23514.272 )3 23513.687 )1 23513.068 )3 23512.42 )3 23511.744 )2 23511.034 )5 23510.295 )6 23509.526 )7 23508.729 )6 23507.898 )8 23507.039 )8 23506.145 )13 23505.24 1 23504.285 )4 23503.309 )0 23502.304 5
23500.157 23499.050 23497.913 23496.751 23495.545 23494.324 23493.067 23491.775 23490.461 23489.100 23487.726 23486.316 23484.877 23483.397 23481.893
3 0 )1 2 )8 )2 )1 )4 1 )9 )3 )0 3 )3 )2
23478.793 23477.199 23475.562 23473.891 23472.211 23470.492 23468.729 23466.941 23465.147 23463.280 23461.407
1 5 )3 )13 )1 3 )7 )8 15 )3 4
23500.187 0 23499.083 )1 23497.95 )3 23496.79 )1 23495.596 )1 23494.378 4 23493.127 7 23491.835 0 23490.524 5 23489.172 )1 23487.796 )0 23486.389 )0 23484.947 )4 23483.481 )0 23481.98 )2 23480.447 )4 23478.89 0 23477.302 4 23475.669 )5 23474.031 11 23472.329 )6 23470.614 )4 23468.879 8 23467.098 6 23465.288 6 23463.431 )10 23461.576 8 23459.66 )5 23457.729 )0
25008.736 25008.453 25008.151 25007.822
0 )4 )2 )3
25008.736 25008.453 25008.151 25007.822
)1 )5 )3 )4
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
11
Table 1 (continued) J
Ree(J)
O)C
14.5 15.5 16.5 17.5 18.5 19.5 20.5 21.5 22.5 23.5 24.5 25.5 26.5 27.5 28.5 29.5 30.5 31.5 32.5 33.5 34.5 35.5 36.5 37.5 38.5 39.5 40.5 41.5 42.5 43.5 44.5 45.5 46.5 47.5 48.5 49.5 50.5 51.5 52.5 53.5 54.5 55.5 56.5 57.5 58.5 59.5 60.5 61.5 62.5 63.5 64.5
25019.367 25019.755 25020.119 25020.473 25020.781 25021.081 25021.345 25021.581 25021.799 25021.995 25022.164 25022.322 25022.440 25022.540 25022.609 25022.655
)4 )6 )7 5 )5 4 )1 )9 )9 )9 )10 2 )0 3 1 )1
25021.029
6
25020.412 25020.050 25019.669 25019.283 25018.844 25018.392 25017.936 25017.439
12 )1 )8 5 )9 )13 6 7
25016.356 25015.784 25015.172 25014.549 25013.913 25013.233 25012.531 25011.805
)1 2 )10 )9 6 3 2 3
Pee(J)
O)C
24995.192 24994.028 24992.834 24991.625 24990.385 24989.123 24987.833 24986.518 24985.180 24983.818 24982.433 24981.004 24979.583 24978.129 24976.643 24975.139 24973.603 24972.056 24970.476 24968.877 24967.248 24965.605 24963.926 24962.215 24960.493 24958.747 24956.974 24955.177 24953.335 24951.514 24949.635
)9 )5 )7 )0 1 3 2 0 )1 )2 )1 )20 )7 )3 )7 )4 )10 )1 )1 3 2 11 8 )3 0 4 4 5 )15 10 2
24945.821 24943.869 24941.896 24939.903 24937.905 24935.847
2 )6 )10 )11 8 )9
24929.573 24927.455
)11 10
Rff(J) 25019.367 25019.755 25020.119 25020.473 25020.781 25021.081 25021.345 25021.581 25021.799 25021.995 25022.164 25022.302 25022.422 25022.523 25022.596 25022.635
25021.930 25021.723 25021.497 25021.238 25020.971 25020.642 25020.335 25019.979 25019.601 25019.196 25018.783 25018.313 25017.836 25017.344 25016.806 25016.250 25015.643 25015.059 25014.434 25013.759
O)C )1 )3 )4 9 0 9 6 )1 )1 1 1 )5 )4 2 4 )2
)0 )4 )2 )8 3 )23 )2 )4 )4 )5 11 )5 )2 11 3 2 )24 )1 5 )12
Pff(J)
O)C
24995.192 24994.028 24992.834 24991.625 24990.385 24989.123 24987.833 24986.518 24985.180 24983.818 24982.433 24981.004 24979.583 24978.129 24976.643 24975.139 24973.603 24972.019 24970.450 24968.840 24967.211 24965.552 24963.878 24962.183 24960.447 24958.690 24956.922 24955.114 24953.291 24951.450 24949.570 24947.678 24945.742 24943.799
)7 )2 )3 5 6 10 9 9 9 9 11 )7 8 14 12 16 13 )13 )1 )4 )3 )7 )2 7 )1 )5 4 )3 0 9 5 12 )0 6
24939.819 24937.791 24935.750 24933.668 24931.582 24929.462
)3 )8 )2 )13 )2 )1
Qef(J)
O)C
Qfe(J)
O)C
25007.468 25007.094 25006.699 25006.274 25005.822 25005.349 25004.854 25004.326 25003.775 25003.213 25002.614 25001.993 25001.344 25000.669 24999.980 24999.257 24998.517
)4 )0 6 7 5 6 10 6 3 13 12 12 9 3 9 5 9
25007.468 25007.094 25006.699 25006.274 25005.822 25005.349 25004.854 25004.326 25003.775 25003.213 25002.614 25001.993 25001.344 25000.679 24999.993 24999.268 24998.531
)6 )3 2 3 0 1 4 )1 )5 4 1 )1 )5 )2 5 )2 2
24996.132 24995.298 24994.430 24993.534 24992.613 24991.667 24990.707 24989.718 24988.703 24987.659 24986.596 24985.506 24984.391 24983.252 24982.090 24980.899 24979.688 24978.446 24977.188 24975.901 24974.585 24973.250 24971.883 24970.484 24969.086 24967.639 24966.178 24964.687 24963.168 24961.635 24960.059
3 11 10 5 0 )5 0 1 2 )2 )2 )2 )3 )3 )1 )4 )1 )5 1 3 )0 3 0 )10 6 )2 2 0 )4 4 )7
24996.155 24995.320 24994.446 24993.559 24992.649 24991.705 24990.753 24989.763 24988.756 24987.719 24986.657 24985.573 24984.461 24983.332 24982.173 24980.984 24979.780 24978.546 24977.281 24976.002 24974.698 24973.360 24972.016 24970.631 24969.211 24967.782 24966.330
)2 3 )6 )5 )2 )7 3 )1 3 2 1 1 )0 5 4 )1 4 3 )3 )0 4 )2 11 8 )5 )2 3
24963.330 24961.809 24960.250 24958.674
)8 4 1 7
Note. O)C are observed minus calculated line positions in units of 103 cm1 .
electronic states and also to predict new transitions that have not yet been observed.
4. Summary The spectrum of TaO has been observed using a microwave discharge of a mixture of TaCl5 and He and the
spectra in the 3000–35 000 cm1 region were recorded at high resolution using a Fourier transform spectrometer. Two new bands observed at 23 520 and 25 010 cm1 have been tentatively assigned as the 0–0 bands of two new 2 D5=2 –2 P3=2 transitions with lower state in common with System I of Al-Khalili et al. [9]. Improved sets of spectroscopic constants have been observed from a combined fit of the lines of the new transitions and the
12
R.S. Ram, P.F. Bernath / Journal of Molecular Spectroscopy 221 (2003) 7–12
Table 2 HundÕs case (c) molecular constants (in cm1 ) for TaO Constantsa T00 B0 107 D0 1013 H0 102 p0 106 pD0 1011 pH 0 ) R0 (A
12 P3=2 0.0b 0.3960362(38) 2.6361(31) 3.430(83)
2
R1=2 (10 025 cm1 )
2
10025.90046(78) 0.3860478(37) 2.6161(27)
23519.70056(75) 0.3809991(39) 2.9044(42)
—
8.4849(33) )1.441(12) 5.775(96) 1.7237729(82)
—
)0.69473(89) —
1.7018963(79)
D5=2 (23 520 cm1 )
2
D5=2 (25 010 cm1 )
25010.20367(81) 0.3838890(40) 2.7976(42)
—
—
—
—
—
—
—
—
1.7351564(97)
1.7286130(97)
a
Numbers in parentheses are one standard deviation in the last two digits quoted. b Fixed value, see text for details.
Table 3 HundÕs case (a) molecular constants (in cm1 ) for TaO R1=2 (10 025 cm1 )
Constantsa
12 P3=2
2
T00 A0 B0 107 D0 1013 H0 104 q0 c0 106 cD0 1011 cH 0 ) R0 (A
0.0b 1000.0c 0.3958795(37) 2.6342(31) 3.416(82) 8.895(11)
10525.93535(77)
— — —
1.7022333(80)
2
D5=2 (23 520 cm1 )
23020.07039(74) 1000.0c 0.3809262(39) 2.9031(41)
—
0.3860461(37) 2.6159(27)
2
D5=2 (25 010 cm1 )
24510.57855(81) 1000.0c 0.3838151(39) 2.7963(41)
—
—
—
—
—
—
—
—
—
—
—
0.856944(34) )2.492(12) 5.818(95) 1.7237767(88)
1.7353224(89)
—
1.7287794(88)
a
Numbers in parentheses are one standard deviation in the last two digits quoted. b Fixed value. c Fixed value, see text for details.
near infrared transition, and a 2 P1=2 assignment is proposed for the excited state of the near infrared transition. Alternatively, our new transitions could be 4 P5=2 –4 R 3=2 transitions and then the excited state of the near infrared transition would be 4 P1=2 . More theoretical work is needed to distinguish between these possibilities and, in particular, to locate the quartet transitions.
Acknowledgments We thank M. Dulick and D. Bransden of the National Solar Observatory for assistance in obtaining the spectra. The National Solar Observatory is operated by the Association of Universities for Research in Astronomy, under contract with the National Science Foundation. The research described here was supported by funding from NASA laboratory astrophysics program. Some support was also provide by the Natural Sciences and Engineering Research Council of Canada.
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