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The ground-state infrared spectra of ytterbium monohydride
3 1 July 1992
CHEMICAL PHYSICS LETTERS
Volume 195, number 5,6
The ground-state infrared spectra of ytterbium monohydride Albert
H. Bahnmaier,
Rolf-Dieter
Urban
and Harold
Jones
Abteilung Physikalische Chemie, Universittit Ulm, W-7900 Urn. Germany Received 8 May 1992; in final form 27 May 1992
The infrared spectra of six isotopomers of YbH in its ground electronic state (‘2) have been measured in the gas phase using a diode laser spectrometer. The experimental data have allowed the determination of a set of accurate Dunham parameters for each isotopomer and a single set of mass-independent parameters.
1. Introduction
The diatomic hydrides represent the simplest possible compound of any individual element and as such are of fundamental importance. However, a survey of the literature reveals the surprising fact that there is very little experimental information available on the monohydrides of the lanthanides. Indeed, it appears that direct spectroscopic information exists only for the monohydrides of Lu [ 1 ] and Yb and moreover, detailed information is only available in the latter case [2-41. As part of our continuing interest in diatomic metal hydrides, e.g. refs. [ 5,6], we have set ourselves the goal of extending our knowledge over the hydrides of the lanthanides and YbH was chosen as the starting point for this project. The information so far available over YbH comes from conventional electronic spectroscopy carried out by Kopp and co-workers [ 2-41 under conditions of only moderate resolution. The present paper reports the results of diode laser measurements of the infrared spectrum of YbH in its *X ground electronic state. Under the conditions of Doppler-limited resolution routinely achieved with diode lasers, transitions of six isotopomers of YbH were resolved. Furthermore, since our measurements were free from the complications of perturbations which were observed in the electronic spectra, the resulting ground Correspondence to: H. Jones, Abteilung Physikalische Chemie, Universitlt Ulm, Postfach 4066, W-7900 Ulm, Germany.
state parameters
can be expected to be more reliable.
2. Experimental The basic approach to the production of diatomic metal hydrides used previously in this laboratory, e.g. refs. [ 5,6], was to react metal vapor with hydrogen in a ceramic tube at high temperatures. However, it was very soon determined that aluminium oxide tubes were unsuitable for use with ytterbium. Several grams of ytterbium metal were placed in an alumina tube in an atmosphere of hydrogen ( = 10 mbar). As the temperature of the tube rose to around 600°C the first lines of YbH appeared, but disappeared within a few minutes. On raising the temperature of the tube to 1200°C the lines reappeared briefly and then disappeared again. The ytterbium metal appears to be bound by reaction with the alumina. Since these measurements on YbH were to serve as a pilot project for later measurements on other (much more expensive) lanthanides, considerable effort was devoted to optimizing the conditions for the production of the hydride. Our experience with other diatomic metal hydrides has shown that it was frequently advantageous to be able to subject the metal vapor/hydrogen reaction mixture to an electric discharge. This requirement precludes the use of a conducting material for the cell which in turn limits the range of materials which come into question. The most suitable material so far found proved to be ZrOz ceramic, and
0009-2614/92/$ 05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.
609
Volume 195, number
5,6
CHEMICAL
PHYSICS
the measurements reported here were all carried out in a tube of this material at a temperature of = 650°C. One charge of = 5 g of ytterbium was sufficient to allow spectra to be observed over several days. However, subsequent attempts to observe the spectra of YbD in a new Zr02 tube from the same manufacturer failed to produce equivalent results. Evidently the production of Yb-metal vapor in the cell is critically dependent on the exact composition of the tube used. Further experiments with aluminium oxide tubes partially lined with various metal foils (tantalum, niobium) failed to produce satisfactory results and we are still searching for better cell material for the production of the hydrides of lanthanides. The diode laser spectrometer used was based on the laser head assembly of Laser Photonics with diodes from the same company. Measurements were carried out to a nominal accuracy of 0.001 cm- ’ using a calibrated confocal Ctalon with a FSR of
0.009763 cm- ’ in conjunction with accurately measured absorption lines. Absolute wavenumber calibration was carried out using accurately known absorption lines of NH3 [ 7 1, SO, [ 8 ] and formaldehyde [ 9 1. The diode laser beam was passed axially through the cell onto a HgCdTe infrared detector. Signals were processed by source modulation of the diode laser at 10 kHz followed by phase sensitive detection.
3. Spectra Since six of the seven isotopes of ytterbium have natural abundances ranging from 4% to 29% and the spin-rotation coupling gives rise to a doublet structure for each line, each rovibrational transition was observed as a characteristic pattern of six doublets of varying intensity. An example of such a pattern is shown in fig. 1. Using the ground state parameters
R(10.5)
R(9.5)
1280.0
1280.2
31 July 1992
LETTERS
1280.4
1280.6
cm-’
Fig. 1. The R( 10) transition of the fundamental band of YbH near 1280.4 cm- ’ which is split into two components (indicated as R( 9.5 ) and R( 10.5) ) by the spin-rotation coupling. The lines arising from the individual are indicated as: a= 176YbH ( 13%), b= ‘?bH (29%), c=“~Y~H (17%), d=“‘YbH (21%), e=“‘YbH (14%), f=“‘YbH (4%). The apparent intensity difference between the two spin components in the figure arises from variation of diode laser power across the region of measurement.
610
Volume 195, number
CHEMICAL
5,6
PHYSICS
determined by Hagland et al. [ 21 little difficulty was encountered in making the first assignments. In all some 330 lines were measured in the fundamental and the first hot-band, with rotational quantum numbers ranging up to N= 20. A complete listing of the lines measured may be obtained from the authors.
The entire data set can be fitted to a single set of mass-independent parameters ( U,J,G,) [ 111 and the Dunham expression becomes: E= 1 /r(“2+‘)Uij[
Since the ground state of YbH has 2Z configuration, the data of each individual isotopomer were first fitted to the usual Dunham expression [ lo] for the energy levels of a diatomic molecule extended to include the effects of the spin-rotational coupling, i.e. F= 1 Yo(v+j)‘[N(N+
l)]’
ij
~~(v+$)‘[N(N+l)]j-’
forJ=N+j,
F= 1 Y,(U+f)‘[N(N+l)]’ iJ
forJ=N-f
.
Table 1 Dunham coeffkients
6 (cm-‘) lines ‘) Numbers
where ,Uis the reduced mass of the molecule, M(M) is the ratio of the mass of the electron to the mass of the ytterbium atom and LIP are the mass scaling coefficients for this atom. However, in this case, since only isotopomers of the heavy atom (Yb ) were measured the mass scaling coefftcients (d,) could not be determined and were set to zero: i.e. in this case the simple reduced mass relationship between two isotopic species, 7
5. Discussion
The parameters fitted and the values obtained are shown in table 1 for each of the six isotopic species investigated. The values of these parameters available at the beginning of this work [ 21 are included in this table for comparison.
YOI Y,,X102 YOZX10S YlZX 106
l)]‘,
where ,u and ,u* are the reduced masses, is sufficient to reproduce the present data accurately. The values for the mass-independent parameters determined are shown in table 2.
lJ
Y20 YO, y,,x10* Y2,x103 Y,,X lo4 Y,*x lo6
(u+t)‘[N(N+
y;. = (P/P*) (1+2j)/2YIJ
+tNC
Y10
1 +M(M)df]
0
x
4. Analysis
31 July 1992
LETTERS
and spin-rotation
coupling
constants
As can be seen from table 1, the results of the present work essentially confirm those obtained previously from conventional electronic spectroscopy, but are much more accurate. The higher resolution
of YbH (cm -
’ ) a)
“0ybH
“‘YbH
’ 'WH
“3YbH
“‘WH
’ 'WH
Ref. [2]
1249.6228( 14) -21.05717(52) 3.993589(41) -9.6178(17) - 1.0084(52) - 1.6104( 13) - 1.048(25) 0.58496(93) -3.144( 10) -6.63(24) 5.05(60)
1249.6020( 12) -21.05667(42) 3.99341 l(32) -9.6172( 13) - 1.0086(42) - 1.6094( 10) - 1.034( 18) 0.58645(74) -3.1223(76) -6.88(21) 3.86(35)
1249.5828( 10) -21.05687(34) 3.993293(31) -9.6183( 12) -0.9992(37) - 1.6098( 10) -1.061(18) 0.58631(64) -3.1291(72) -6.99(20) 4.15(33)
1249.5586( 16) -21.05468(57) 3.993113(41) -9.6155(17) - 1.0101(55) - 1.6086( 13) - 1.043(22) 0.5828( 10) -3.1287(96) -6.59(28) 3.97(45)
1249.5406( 10) -21.05519(35) 3.993050(31) -9.6178( 12) -0.9992(37) - 1.6106( 10) -1.041(18) 0.58589(64) -3.1261(73) -6.89(20) 3.98(34)
1249.5008( 10) -21.05411(35) 3.992804(31) -9.6178(13) -09962(38) -1.6110(10) - 1.036( 18) 0.58603(65) -3.1260(74) -7.01(20) 4.15(34)
1249.54(3) -21.055(9) 3.995(l) -9.86(7) -1.618(l) -1.7(l) 0.583 -3.0 -
0.0012 34 in parentheses
0.0015 56 represent
1 standard
0.0015 63 deviation
0.0018 54
0.0015 63
0.0015 61
in units of the last digit.
611
Volume 195, number 5,6 Table 2 Mass-independent amu’12-J) a)
parameters
CHEMICAL PHYSICS LETTERS
determined
for YbH (cm-’
YbH UlO &O UO,
ci,,x r/,, x r/,,x u,zx
102 10) 104 lo6
701
Y,,X102 YZlX104 Yo2X105 Y12X106 S (cm-‘) lines
1250.8009(4) -21.09744(15) 4.001094( 12) -9.64598(53) - 1.0076( 16) -1.61630(41) - 1.0454( 74) 0.58612(29) -3.0944(59) -1.59(18) -6.704(88) 4.30( 14) 0.0014 331
ai Numbers in parentheses represent 1 standard deviation in units of the last digit.
available in the diode laser measurements has enabled molecular parameters for individual isotopomers of YbH to be determined for the first time. The increase in accuracy is particularly prominent in the case of the spin-rotational parameters (table 1) which were only roughly determined in the older work. As already indicated in section 1, the observation of the diode laser spectrum of YbH is particularly important for the extension of this work to other lan-
612
31 July 1992
thanides for which no experimental information at all is available, However, the success of this project is dependent on the determination of reproducible conditions which will allow spectra of YbH to be observed reliably for extended periods of time with only moderate metal consumption.
Acknowledgement
This work is supported by the Deutsche Forschungsgemeinschaft and in part by the Fonds der Chemischen Industrie.
References [ 1] C. Effantin and J. DIncan, Can. J. Phys. 51 ( 1973) 1394. [2] L. Hagland, I. Kopp and N. Aslund, Arkiv. Fysik. 32 ( 1966) 321. [ 31 L. Hagland, I. Kopp, Arkiv. Fysik. 39 ( 1968) 257. [4] I. Kopp and L. Hagland, Can. J. Phys. 53 (1975) 2242. [ 5 ] R.D. Urban, U. Magg, H. Birk and H. Jones, J. Chem, Phys. 92 (1990) 14. [ 61 H. Birk, R.D. Urban, P. Polomsky and H. Jones, J. Chem. Phys. 94 (1991) 5435. [7] G. Guelachvili and K.N. Rao, Handbook of infrared standards (Academic Press, New York, 1986). [8] G. Guelachvili, O.N. Ulenikov and G.A. Yshakova, J. Mol. Spectty. 108 (1984) 1. [9] S. Nadler, D.C. Reuter, S.J. Daunt and J.W.C. Johns, NASA technical memorandum 100709 ( 1988). [IO] J.L. Dunham, Phys. Rev. 41 (1932) 721. [ 111 J.K.G. Watson, J. Mol. Spectry. 80 ( 1980) 411.
CHEMICAL PHYSICS LETTERS
Volume 195, number 5,6
The ground-state infrared spectra of ytterbium monohydride Albert
H. Bahnmaier,
Rolf-Dieter
Urban
and Harold
Jones
Abteilung Physikalische Chemie, Universittit Ulm, W-7900 Urn. Germany Received 8 May 1992; in final form 27 May 1992
The infrared spectra of six isotopomers of YbH in its ground electronic state (‘2) have been measured in the gas phase using a diode laser spectrometer. The experimental data have allowed the determination of a set of accurate Dunham parameters for each isotopomer and a single set of mass-independent parameters.
1. Introduction
The diatomic hydrides represent the simplest possible compound of any individual element and as such are of fundamental importance. However, a survey of the literature reveals the surprising fact that there is very little experimental information available on the monohydrides of the lanthanides. Indeed, it appears that direct spectroscopic information exists only for the monohydrides of Lu [ 1 ] and Yb and moreover, detailed information is only available in the latter case [2-41. As part of our continuing interest in diatomic metal hydrides, e.g. refs. [ 5,6], we have set ourselves the goal of extending our knowledge over the hydrides of the lanthanides and YbH was chosen as the starting point for this project. The information so far available over YbH comes from conventional electronic spectroscopy carried out by Kopp and co-workers [ 2-41 under conditions of only moderate resolution. The present paper reports the results of diode laser measurements of the infrared spectrum of YbH in its *X ground electronic state. Under the conditions of Doppler-limited resolution routinely achieved with diode lasers, transitions of six isotopomers of YbH were resolved. Furthermore, since our measurements were free from the complications of perturbations which were observed in the electronic spectra, the resulting ground Correspondence to: H. Jones, Abteilung Physikalische Chemie, Universitlt Ulm, Postfach 4066, W-7900 Ulm, Germany.
state parameters
can be expected to be more reliable.
2. Experimental The basic approach to the production of diatomic metal hydrides used previously in this laboratory, e.g. refs. [ 5,6], was to react metal vapor with hydrogen in a ceramic tube at high temperatures. However, it was very soon determined that aluminium oxide tubes were unsuitable for use with ytterbium. Several grams of ytterbium metal were placed in an alumina tube in an atmosphere of hydrogen ( = 10 mbar). As the temperature of the tube rose to around 600°C the first lines of YbH appeared, but disappeared within a few minutes. On raising the temperature of the tube to 1200°C the lines reappeared briefly and then disappeared again. The ytterbium metal appears to be bound by reaction with the alumina. Since these measurements on YbH were to serve as a pilot project for later measurements on other (much more expensive) lanthanides, considerable effort was devoted to optimizing the conditions for the production of the hydride. Our experience with other diatomic metal hydrides has shown that it was frequently advantageous to be able to subject the metal vapor/hydrogen reaction mixture to an electric discharge. This requirement precludes the use of a conducting material for the cell which in turn limits the range of materials which come into question. The most suitable material so far found proved to be ZrOz ceramic, and
0009-2614/92/$ 05.00 0 1992 Elsevier Science Publishers B.V. All rights reserved.
609
Volume 195, number
5,6
CHEMICAL
PHYSICS
the measurements reported here were all carried out in a tube of this material at a temperature of = 650°C. One charge of = 5 g of ytterbium was sufficient to allow spectra to be observed over several days. However, subsequent attempts to observe the spectra of YbD in a new Zr02 tube from the same manufacturer failed to produce equivalent results. Evidently the production of Yb-metal vapor in the cell is critically dependent on the exact composition of the tube used. Further experiments with aluminium oxide tubes partially lined with various metal foils (tantalum, niobium) failed to produce satisfactory results and we are still searching for better cell material for the production of the hydrides of lanthanides. The diode laser spectrometer used was based on the laser head assembly of Laser Photonics with diodes from the same company. Measurements were carried out to a nominal accuracy of 0.001 cm- ’ using a calibrated confocal Ctalon with a FSR of
0.009763 cm- ’ in conjunction with accurately measured absorption lines. Absolute wavenumber calibration was carried out using accurately known absorption lines of NH3 [ 7 1, SO, [ 8 ] and formaldehyde [ 9 1. The diode laser beam was passed axially through the cell onto a HgCdTe infrared detector. Signals were processed by source modulation of the diode laser at 10 kHz followed by phase sensitive detection.
3. Spectra Since six of the seven isotopes of ytterbium have natural abundances ranging from 4% to 29% and the spin-rotation coupling gives rise to a doublet structure for each line, each rovibrational transition was observed as a characteristic pattern of six doublets of varying intensity. An example of such a pattern is shown in fig. 1. Using the ground state parameters
R(10.5)
R(9.5)
1280.0
1280.2
31 July 1992
LETTERS
1280.4
1280.6
cm-’
Fig. 1. The R( 10) transition of the fundamental band of YbH near 1280.4 cm- ’ which is split into two components (indicated as R( 9.5 ) and R( 10.5) ) by the spin-rotation coupling. The lines arising from the individual are indicated as: a= 176YbH ( 13%), b= ‘?bH (29%), c=“~Y~H (17%), d=“‘YbH (21%), e=“‘YbH (14%), f=“‘YbH (4%). The apparent intensity difference between the two spin components in the figure arises from variation of diode laser power across the region of measurement.
610
Volume 195, number
CHEMICAL
5,6
PHYSICS
determined by Hagland et al. [ 21 little difficulty was encountered in making the first assignments. In all some 330 lines were measured in the fundamental and the first hot-band, with rotational quantum numbers ranging up to N= 20. A complete listing of the lines measured may be obtained from the authors.
The entire data set can be fitted to a single set of mass-independent parameters ( U,J,G,) [ 111 and the Dunham expression becomes: E= 1 /r(“2+‘)Uij[
Since the ground state of YbH has 2Z configuration, the data of each individual isotopomer were first fitted to the usual Dunham expression [ lo] for the energy levels of a diatomic molecule extended to include the effects of the spin-rotational coupling, i.e. F= 1 Yo(v+j)‘[N(N+
l)]’
ij
~~(v+$)‘[N(N+l)]j-’
forJ=N+j,
F= 1 Y,(U+f)‘[N(N+l)]’ iJ
forJ=N-f
.
Table 1 Dunham coeffkients
6 (cm-‘) lines ‘) Numbers
where ,Uis the reduced mass of the molecule, M(M) is the ratio of the mass of the electron to the mass of the ytterbium atom and LIP are the mass scaling coefficients for this atom. However, in this case, since only isotopomers of the heavy atom (Yb ) were measured the mass scaling coefftcients (d,) could not be determined and were set to zero: i.e. in this case the simple reduced mass relationship between two isotopic species, 7
5. Discussion
The parameters fitted and the values obtained are shown in table 1 for each of the six isotopic species investigated. The values of these parameters available at the beginning of this work [ 21 are included in this table for comparison.
YOI Y,,X102 YOZX10S YlZX 106
l)]‘,
where ,u and ,u* are the reduced masses, is sufficient to reproduce the present data accurately. The values for the mass-independent parameters determined are shown in table 2.
lJ
Y20 YO, y,,x10* Y2,x103 Y,,X lo4 Y,*x lo6
(u+t)‘[N(N+
y;. = (P/P*) (1+2j)/2YIJ
+tNC
Y10
1 +M(M)df]
0
x
4. Analysis
31 July 1992
LETTERS
and spin-rotation
coupling
constants
As can be seen from table 1, the results of the present work essentially confirm those obtained previously from conventional electronic spectroscopy, but are much more accurate. The higher resolution
of YbH (cm -
’ ) a)
“0ybH
“‘YbH
’ 'WH
“3YbH
“‘WH
’ 'WH
Ref. [2]
1249.6228( 14) -21.05717(52) 3.993589(41) -9.6178(17) - 1.0084(52) - 1.6104( 13) - 1.048(25) 0.58496(93) -3.144( 10) -6.63(24) 5.05(60)
1249.6020( 12) -21.05667(42) 3.99341 l(32) -9.6172( 13) - 1.0086(42) - 1.6094( 10) - 1.034( 18) 0.58645(74) -3.1223(76) -6.88(21) 3.86(35)
1249.5828( 10) -21.05687(34) 3.993293(31) -9.6183( 12) -0.9992(37) - 1.6098( 10) -1.061(18) 0.58631(64) -3.1291(72) -6.99(20) 4.15(33)
1249.5586( 16) -21.05468(57) 3.993113(41) -9.6155(17) - 1.0101(55) - 1.6086( 13) - 1.043(22) 0.5828( 10) -3.1287(96) -6.59(28) 3.97(45)
1249.5406( 10) -21.05519(35) 3.993050(31) -9.6178( 12) -0.9992(37) - 1.6106( 10) -1.041(18) 0.58589(64) -3.1261(73) -6.89(20) 3.98(34)
1249.5008( 10) -21.05411(35) 3.992804(31) -9.6178(13) -09962(38) -1.6110(10) - 1.036( 18) 0.58603(65) -3.1260(74) -7.01(20) 4.15(34)
1249.54(3) -21.055(9) 3.995(l) -9.86(7) -1.618(l) -1.7(l) 0.583 -3.0 -
0.0012 34 in parentheses
0.0015 56 represent
1 standard
0.0015 63 deviation
0.0018 54
0.0015 63
0.0015 61
in units of the last digit.
611
Volume 195, number 5,6 Table 2 Mass-independent amu’12-J) a)
parameters
CHEMICAL PHYSICS LETTERS
determined
for YbH (cm-’
YbH UlO &O UO,
ci,,x r/,, x r/,,x u,zx
102 10) 104 lo6
701
Y,,X102 YZlX104 Yo2X105 Y12X106 S (cm-‘) lines
1250.8009(4) -21.09744(15) 4.001094( 12) -9.64598(53) - 1.0076( 16) -1.61630(41) - 1.0454( 74) 0.58612(29) -3.0944(59) -1.59(18) -6.704(88) 4.30( 14) 0.0014 331
ai Numbers in parentheses represent 1 standard deviation in units of the last digit.
available in the diode laser measurements has enabled molecular parameters for individual isotopomers of YbH to be determined for the first time. The increase in accuracy is particularly prominent in the case of the spin-rotational parameters (table 1) which were only roughly determined in the older work. As already indicated in section 1, the observation of the diode laser spectrum of YbH is particularly important for the extension of this work to other lan-
612
31 July 1992
thanides for which no experimental information at all is available, However, the success of this project is dependent on the determination of reproducible conditions which will allow spectra of YbH to be observed reliably for extended periods of time with only moderate metal consumption.
Acknowledgement
This work is supported by the Deutsche Forschungsgemeinschaft and in part by the Fonds der Chemischen Industrie.
References [ 1] C. Effantin and J. DIncan, Can. J. Phys. 51 ( 1973) 1394. [2] L. Hagland, I. Kopp and N. Aslund, Arkiv. Fysik. 32 ( 1966) 321. [ 31 L. Hagland, I. Kopp, Arkiv. Fysik. 39 ( 1968) 257. [4] I. Kopp and L. Hagland, Can. J. Phys. 53 (1975) 2242. [ 5 ] R.D. Urban, U. Magg, H. Birk and H. Jones, J. Chem, Phys. 92 (1990) 14. [ 61 H. Birk, R.D. Urban, P. Polomsky and H. Jones, J. Chem. Phys. 94 (1991) 5435. [7] G. Guelachvili and K.N. Rao, Handbook of infrared standards (Academic Press, New York, 1986). [8] G. Guelachvili, O.N. Ulenikov and G.A. Yshakova, J. Mol. Spectty. 108 (1984) 1. [9] S. Nadler, D.C. Reuter, S.J. Daunt and J.W.C. Johns, NASA technical memorandum 100709 ( 1988). [IO] J.L. Dunham, Phys. Rev. 41 (1932) 721. [ 111 J.K.G. Watson, J. Mol. Spectry. 80 ( 1980) 411.