- Email: [email protected]
Absorption spectrum of the f(A1g) ← X(Eg), a(F2g) electronic transition of OsF6
SPECTROCHIMICA ACTA PART
ELSEVIER
A
Spectrochimica Acta Part A 53 (1997) 991-994
Absorption spectrum of the f(A,,) + X(E,), a(F,,) transition of OsF,
electronic
M. Rotgq a**, V. Boudon a, H. Selig b a Laboratoire de Physique de I’Universit8 de Bourgogne, ’ Department of Inorganic and Analytical Chemistry,
(Unit6 associie au CNRS), BP 400-21011 Dijon, Cedex, France The Hebrew University of Jerusalem, Jerusalem 91904, Lrrael
Received 22 November 1996: accepted 30 December 1996
Abstract The absorption spectrum of the visible band of OsF, hasbeenrecordedusinga commercialspectrophotometer.The first vibronic assignments for this band have beenrealized usingthe analogy with the dt X transition of IrF,. Some vibronic parametervalues are derived. 0 1997Elsevier ScienceB.V. Keywords:
Osmiumhexafluoride; Absorption spectroscopy;Vibronic transitions
In a previous paper [l], we have analyzed in detail the vibronic bands of IrF,. We present here a preliminary study of another third-row transition-metal hexafluoride, namely OsF,. There are only a very few studies on the near-infrared and visible absorption spectroscopy of this molecule. Mofht et al. [2], and more recently Holloway et al. [3] have recorded low-resolution spectra, but without giving any assignment of the vibronic bands. Michalopoulos and Bernstein [4] have performed a more detailed study, but only concerning the solid phase. Osmium hexafluoride possesses a very complex vibronic absorption band system in the 3700- 18 600 cm - ’ region, with accidental near degeneracies of some of the seven low-lying electronic states. Moreover, five of these electronic states are strongly perturbed by Jahn-Teller cou* Corresponding author. Tel.: + 33 380395967; fax: + 33 380395971; e-mail: [email protected]
plings [5,6]. Thus, up to now, no vibronic assignment has been performed for this molecule. In this paper, we present a detailed analysis and parameter values concerning the visible band of OsF,, since this is the most simple one to study because it corresponds to a transition to the totally symmetric f electronic state, which is well isolated from the others. Osmium hexafluoride is a pale-yellow gas, with a vapour pressure of 266 torr at 300 K 171.One of us, H. Selig, has filled a 2 cm length quartz cell with this substance, using a method similar to that described in Ref. [l]. The lower part of Fig. 1 shows the absorption spectrum of the f(A,,) c X(E,), a(F,,) transition, recorded using a Cary 5E (Varian) commercial spectrophotometer. The apparatus resolution was a few wavenumbers in this region. This is the first detailed spectrum of this band. The upper part of Fig. 1 recalls the spectrum of the d(E&)+-X(Gb)
1386-1425/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved.
PII SO584-8539(97)00016-O
992
hf. Rotger
rt al. lSpectrochimica
Acta
Part
.A 53 (1997)
991-994
Fig. 1. Comparison between the absorption spectra of the d(E&) + X(Gk) transition of IrF, and the,f(A,,) + X(E,), u(F,,) transition of OsF, (wavenumber in cm-‘).
Fig. 2. Absorption spectrum of the f(A,,) + X(E,), a(F,,) transition (wavenumber in cm ‘). with observed and calculated posltlons. The vi and V; + \t; band profiles are displayed on the right.
transition of IrF, obtained using the same apparatus (see Ref. [l]). Since the f(A,,) state of OsF, and the d(E&) one of IrF, are unperturbed by complex vibronic couplings (due to their symmetry) both spectra should be very similar. So, we have used the IrF, spectrum to make a rough assignment of the OsF, one. We have
peak
identified here three main features that are the hot band region, the vb, vi region and the vi one. The v’, + vi region is also easily identified thanks to its band profile which is identical to that of v> (see Fig. 2). Then, more detailed assignments have been obtained using the following simple hypotheses:
M. Table 1 Assignments Peak no.
and fit for the f(A,,) “,bs
tcm-‘)
Rotger
+ X(EJ,
et al. /Spectrochimica
a(F,,)
Acta
Part
A 53 (1997)
991-994
transition
Assignment
vcalc (cm - ’ 1
x (cm-‘)
“ohs-
yO
I
16 796.8
9
2 3
16 806.3 16 822.2
? f‘+a+vy
45 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
16 837.0 851.7 16 898.2 16 907.7 16 936.2 16 963.7 17 040.8 17 055.5 17 132.7 17 228.8 17 263.1 17 293.2 17 334.2 17 502.3 17 544.0 17 577.7 17 616.4 17 789.7 17 827.7 17 915.2 17 990.0 18 033.1 18 069.5 18 128.6 18 519.3 18 557.4 18 716.9 18 794.8
;+x+“y f-U+\‘;: ? f+-x+!J;y 1 ?
16 851.7 16 896.9
-284.7
16 932.4
- 200.2
f+v~CX+v~x
17 17 17 17 17 17 17 17 17 17 17 17 17 17 18 18
059.3 136.4 224.1 263.3 296.7 335.9 503.5 542.8 576.2 615.4 790.3 829.6 916.5 989.9 029.1 069.8
18 18 18 18
517.5 556.8 717.1 797.0
f+X f+vk+a
.f+vg+x f+v>+-a f+vl+-X
.f+v;+vk+-a f+v;+v;-x f+v&+v;+a
.f’+v;+v;+x “f+ v; t CI Jfv;tx f+v;+v>+vbca+vg f+v>+vi+-a f’+v;+v;+-x
.f’+v;+v;+-a ? f+v;+v;+-a f‘+v;+v,tx f+v;+v;+vi+a f+v;+v;+v\+-a
16 822.2
frequencies of mode i in the f(A,,), (3 v,“.Y and v:” are the vibrational the wavenumbers for the f(A,,) + X(E,) and f(A,,) +a(Fa,) origins.
l
l
l
993
The a(F,,) electronic state of OsF, lies at very low energy and is therefore thermally populated at room temperature. Thus, transitions arise from both the X(E.J and a(F,,) states, i.e. they should appear two times. The origins of the electronic transitions f(A,,) t X(E,) and f(A,,) +- a(F,J must be extremely weak, since they correspond to symmetry forbidden transitions. Hot band assignments have been realized using the ground electronic state vibrational frequencies given in Ref. [8] and assuming that these frequencies do not differ too much for the u(F,J electronic state.
vobs - v;; (cm - ’ )
- 274.8
- 199.0
- 80.9 -3.7 131.6 127.3 196.0 197.8 405.1 407.6 480.5 480.0 692.5 691.3 818.0 892.8 896.7 972.3 1422.1 1421.0 1619.7 1697.6
X(E,) and a(F,,) electronic states, respectively. Peak numbers are the same as in Fig. 2.
vc and vz are
In Table 1, we give the observed frequencies and the result of the fit that we have realized using a least-squares method. The corresponding peak positions (observed and calculated) are displayed at the top of Fig. 2. As we mentioned before, the origins of the electronic transitions are extremely weak (f(A,,) t u(F,,J being even invisible). Generally speaking, the whole band has a rather low intensity. Table 2 gives the values of the vibronic parameters obtained from the data of Table 1. The standard deviations are given in parenthesis in the units of the last two figures of the parameters. We find that the first electronic state u(F,,) lies at only - 40 cm - ‘. Thus, around
994
M. Rotger
et al. /I Spectrochimica
Acta Part
A 5.7 (1997)
991-994
Table 2 Vibronic parameters for OsF, (in cm-‘) Electronic state X(E,) u(F~~) ,tlA,,)
vu
~‘,(A,,)
WI,)
733 -727.2 (2.1)
720"
~‘e(F,u)
0 39.2 (1.5) 17136.4 (1.6)
284.7 (3.4) 272" 275.0 (3.5) 199.5 (1.5)
693.1 (1.6)
v,(Fz,) 276" 279.4 (1.6)
vg(Fd 204.0 (2.6) 205" 200.3 (2.5) 126.9 (1.7)
The column 18”gives the energies of the electronic states. I’ From Ref. [8].
56% of the molecules are in this state at 300 K. The values of the vibrational wavenumbers (v4 and v6) that we deduce for the X(E,), u(F,,) ground electronic state doublet are consistent with those found in the literature [8]. Seven unattributed bands are also listed in Table 1. This preliminary study will now be used as a starting point for the global analysis of the five electronic bands of OsF,. In particular, the Jahn-Teller parameters in the b(F,,), d(F,,) and e(E,) states are still to be determined. Furthermore, the structure of the X(E,), a(F,,) ground electronic state doublet should be examined using Raman or infrared spectroscopy.
References [I] V. Boudon, M. Rotger and D. Avignant, J. Mol. Spectrosc., 175 (1996) 327. [Z] W. Moffit, G.L. Goodman, M. Fred and B. Weinstock. Mol. Phys., 2 (1959) 109. [3] J.H. Holloway, E.G. Hope, G. Stanger and D.A. Boyd, J. Fluor. Chem., 56 (1992) 77. [4] D.L. Michalopoulos and E.R. Bernstein, Mol. Phys., 47(l) (1982) 1. [5] V. Boudon and F. Michelot, J. Mol. Spectrosc.. 165 (1994) 554. [6] V. Boudon, F. Michelot and J. Moret-Bailly. J. Mol. Spectrosc., 166 (1994) 449. [7] G.H. Cady and B. Hargreaves. J. Chem. Sot., (1961) 1563. [S]
B. Weinstock and G.L. Goodman, Adv. Chem. Phys., 9 (1964) 169.
ELSEVIER
A
Spectrochimica Acta Part A 53 (1997) 991-994
Absorption spectrum of the f(A,,) + X(E,), a(F,,) transition of OsF,
electronic
M. Rotgq a**, V. Boudon a, H. Selig b a Laboratoire de Physique de I’Universit8 de Bourgogne, ’ Department of Inorganic and Analytical Chemistry,
(Unit6 associie au CNRS), BP 400-21011 Dijon, Cedex, France The Hebrew University of Jerusalem, Jerusalem 91904, Lrrael
Received 22 November 1996: accepted 30 December 1996
Abstract The absorption spectrum of the visible band of OsF, hasbeenrecordedusinga commercialspectrophotometer.The first vibronic assignments for this band have beenrealized usingthe analogy with the dt X transition of IrF,. Some vibronic parametervalues are derived. 0 1997Elsevier ScienceB.V. Keywords:
Osmiumhexafluoride; Absorption spectroscopy;Vibronic transitions
In a previous paper [l], we have analyzed in detail the vibronic bands of IrF,. We present here a preliminary study of another third-row transition-metal hexafluoride, namely OsF,. There are only a very few studies on the near-infrared and visible absorption spectroscopy of this molecule. Mofht et al. [2], and more recently Holloway et al. [3] have recorded low-resolution spectra, but without giving any assignment of the vibronic bands. Michalopoulos and Bernstein [4] have performed a more detailed study, but only concerning the solid phase. Osmium hexafluoride possesses a very complex vibronic absorption band system in the 3700- 18 600 cm - ’ region, with accidental near degeneracies of some of the seven low-lying electronic states. Moreover, five of these electronic states are strongly perturbed by Jahn-Teller cou* Corresponding author. Tel.: + 33 380395967; fax: + 33 380395971; e-mail: [email protected]
plings [5,6]. Thus, up to now, no vibronic assignment has been performed for this molecule. In this paper, we present a detailed analysis and parameter values concerning the visible band of OsF,, since this is the most simple one to study because it corresponds to a transition to the totally symmetric f electronic state, which is well isolated from the others. Osmium hexafluoride is a pale-yellow gas, with a vapour pressure of 266 torr at 300 K 171.One of us, H. Selig, has filled a 2 cm length quartz cell with this substance, using a method similar to that described in Ref. [l]. The lower part of Fig. 1 shows the absorption spectrum of the f(A,,) c X(E,), a(F,,) transition, recorded using a Cary 5E (Varian) commercial spectrophotometer. The apparatus resolution was a few wavenumbers in this region. This is the first detailed spectrum of this band. The upper part of Fig. 1 recalls the spectrum of the d(E&)+-X(Gb)
1386-1425/97/$17.00 0 1997 Elsevier Science B.V. All rights reserved.
PII SO584-8539(97)00016-O
992
hf. Rotger
rt al. lSpectrochimica
Acta
Part
.A 53 (1997)
991-994
Fig. 1. Comparison between the absorption spectra of the d(E&) + X(Gk) transition of IrF, and the,f(A,,) + X(E,), u(F,,) transition of OsF, (wavenumber in cm-‘).
Fig. 2. Absorption spectrum of the f(A,,) + X(E,), a(F,,) transition (wavenumber in cm ‘). with observed and calculated posltlons. The vi and V; + \t; band profiles are displayed on the right.
transition of IrF, obtained using the same apparatus (see Ref. [l]). Since the f(A,,) state of OsF, and the d(E&) one of IrF, are unperturbed by complex vibronic couplings (due to their symmetry) both spectra should be very similar. So, we have used the IrF, spectrum to make a rough assignment of the OsF, one. We have
peak
identified here three main features that are the hot band region, the vb, vi region and the vi one. The v’, + vi region is also easily identified thanks to its band profile which is identical to that of v> (see Fig. 2). Then, more detailed assignments have been obtained using the following simple hypotheses:
M. Table 1 Assignments Peak no.
and fit for the f(A,,) “,bs
tcm-‘)
Rotger
+ X(EJ,
et al. /Spectrochimica
a(F,,)
Acta
Part
A 53 (1997)
991-994
transition
Assignment
vcalc (cm - ’ 1
x (cm-‘)
“ohs-
yO
I
16 796.8
9
2 3
16 806.3 16 822.2
? f‘+a+vy
45 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31
16 837.0 851.7 16 898.2 16 907.7 16 936.2 16 963.7 17 040.8 17 055.5 17 132.7 17 228.8 17 263.1 17 293.2 17 334.2 17 502.3 17 544.0 17 577.7 17 616.4 17 789.7 17 827.7 17 915.2 17 990.0 18 033.1 18 069.5 18 128.6 18 519.3 18 557.4 18 716.9 18 794.8
;+x+“y f-U+\‘;: ? f+-x+!J;y 1 ?
16 851.7 16 896.9
-284.7
16 932.4
- 200.2
f+v~CX+v~x
17 17 17 17 17 17 17 17 17 17 17 17 17 17 18 18
059.3 136.4 224.1 263.3 296.7 335.9 503.5 542.8 576.2 615.4 790.3 829.6 916.5 989.9 029.1 069.8
18 18 18 18
517.5 556.8 717.1 797.0
f+X f+vk+a
.f+vg+x f+v>+-a f+vl+-X
.f+v;+vk+-a f+v;+v;-x f+v&+v;+a
.f’+v;+v;+x “f+ v; t CI Jfv;tx f+v;+v>+vbca+vg f+v>+vi+-a f’+v;+v;+-x
.f’+v;+v;+-a ? f+v;+v;+-a f‘+v;+v,tx f+v;+v;+vi+a f+v;+v;+v\+-a
16 822.2
frequencies of mode i in the f(A,,), (3 v,“.Y and v:” are the vibrational the wavenumbers for the f(A,,) + X(E,) and f(A,,) +a(Fa,) origins.
l
l
l
993
The a(F,,) electronic state of OsF, lies at very low energy and is therefore thermally populated at room temperature. Thus, transitions arise from both the X(E.J and a(F,,) states, i.e. they should appear two times. The origins of the electronic transitions f(A,,) t X(E,) and f(A,,) +- a(F,J must be extremely weak, since they correspond to symmetry forbidden transitions. Hot band assignments have been realized using the ground electronic state vibrational frequencies given in Ref. [8] and assuming that these frequencies do not differ too much for the u(F,J electronic state.
vobs - v;; (cm - ’ )
- 274.8
- 199.0
- 80.9 -3.7 131.6 127.3 196.0 197.8 405.1 407.6 480.5 480.0 692.5 691.3 818.0 892.8 896.7 972.3 1422.1 1421.0 1619.7 1697.6
X(E,) and a(F,,) electronic states, respectively. Peak numbers are the same as in Fig. 2.
vc and vz are
In Table 1, we give the observed frequencies and the result of the fit that we have realized using a least-squares method. The corresponding peak positions (observed and calculated) are displayed at the top of Fig. 2. As we mentioned before, the origins of the electronic transitions are extremely weak (f(A,,) t u(F,,J being even invisible). Generally speaking, the whole band has a rather low intensity. Table 2 gives the values of the vibronic parameters obtained from the data of Table 1. The standard deviations are given in parenthesis in the units of the last two figures of the parameters. We find that the first electronic state u(F,,) lies at only - 40 cm - ‘. Thus, around
994
M. Rotger
et al. /I Spectrochimica
Acta Part
A 5.7 (1997)
991-994
Table 2 Vibronic parameters for OsF, (in cm-‘) Electronic state X(E,) u(F~~) ,tlA,,)
vu
~‘,(A,,)
WI,)
733 -727.2 (2.1)
720"
~‘e(F,u)
0 39.2 (1.5) 17136.4 (1.6)
284.7 (3.4) 272" 275.0 (3.5) 199.5 (1.5)
693.1 (1.6)
v,(Fz,) 276" 279.4 (1.6)
vg(Fd 204.0 (2.6) 205" 200.3 (2.5) 126.9 (1.7)
The column 18”gives the energies of the electronic states. I’ From Ref. [8].
56% of the molecules are in this state at 300 K. The values of the vibrational wavenumbers (v4 and v6) that we deduce for the X(E,), u(F,,) ground electronic state doublet are consistent with those found in the literature [8]. Seven unattributed bands are also listed in Table 1. This preliminary study will now be used as a starting point for the global analysis of the five electronic bands of OsF,. In particular, the Jahn-Teller parameters in the b(F,,), d(F,,) and e(E,) states are still to be determined. Furthermore, the structure of the X(E,), a(F,,) ground electronic state doublet should be examined using Raman or infrared spectroscopy.
References [I] V. Boudon, M. Rotger and D. Avignant, J. Mol. Spectrosc., 175 (1996) 327. [Z] W. Moffit, G.L. Goodman, M. Fred and B. Weinstock. Mol. Phys., 2 (1959) 109. [3] J.H. Holloway, E.G. Hope, G. Stanger and D.A. Boyd, J. Fluor. Chem., 56 (1992) 77. [4] D.L. Michalopoulos and E.R. Bernstein, Mol. Phys., 47(l) (1982) 1. [5] V. Boudon and F. Michelot, J. Mol. Spectrosc.. 165 (1994) 554. [6] V. Boudon, F. Michelot and J. Moret-Bailly. J. Mol. Spectrosc., 166 (1994) 449. [7] G.H. Cady and B. Hargreaves. J. Chem. Sot., (1961) 1563. [S]
B. Weinstock and G.L. Goodman, Adv. Chem. Phys., 9 (1964) 169.