- Email: [email protected]
Nuclear quadrupole coupling constants of thionyl chloride
CHEMICAL PHYSICS 1 (1973) 441443.
NORTH-HOLLAND
PUBLISHING
COMPANY
NUCLEARQUADRUPOLECOUPLlNGCONSTANTSOFTHlONYL Luboratory
H.U. WENGER, A. BAUDER and Hs.H. GiiNTHARD Swiss Fedeml Instirute of Technolom, 1X4006
for Physical Chemisrry,
CHLORIDE Zurich. Switrerlond
Received I June 1973 The nuclear qundrupole structure of some low I transitions with large splittings has been measured for thionyl chloride (S03”C12) and analysed in terms of a first order perturbation. The following nuclear quadrupole coupling constants were obtained: 16~ = -25.01 f 0.07 MHz. Xbb = -0.03 i 0.45 hlHz and qc = 25.04 2 0.45 hlHz.
Tbionyl chloride has, even at low frequencies, an extremely rich microwave spectrum as has been pointed out by several authors [l-3]. The low J transitions are comparatively weak. Several isotopic species in nat. unl abundance, complicated nuclear quadrupole splitting patterns originating from two nuclei and excited vibrational states are responsible for this observation. We first failed to directly assign low J transitions on the basis of nuclear quadrupole splittings and Stark effect due to overlapping absorption lines and interfering Stark lobes. Joumel and collaborators [l, 3-51 have given an assignment of R- and Q-branch transitions by systematically investigating the general behaviour of the strongest high J transitions. Only approximate values for the nuclear quadrupole coupling constants were reported [ 11. Medium and high J transitions have been assigned exclusively and their small nuclear hyperfine splittings of around 1 MHz did not warrant a rigorous analysis. In this paper we present the results of the analysis of the nuclear quadrupole splittings of three low J rotational transitions of SO%2. The nuclear quadrupole splitting pattern due to two identical nuclei of a rotational transition is calculated using a first order perturbation treatment in the I,I, IJ F MF representation [6]. The relative intensities of the hyperfine components are obtained by transforming the line strengths in the I, I,IJ FMFscheme with the transformation coefficients which diagonalize the first order perturbation matrices. Following the selection rules AI = 0, + 1 and AF = 0, + 1, the transition frequencies of all possible hyperfine components
with their intensities are calculated. In addition, an actual picture of the nuclear quadrupole multiplet structure is produced by a plotler, assuming lorentzian line shapes of equal line widths for alJ hyperfime components. A description of the computer program for the calculations is given in ref. [2]. Using the Q-branch assignment of Burie et al. [4] and extrapolating it to low J transitions, we were able to identify the three tmnsitions S,, - S4,, 836 - 8, and 9s4 - 9.,6_ They were just strong enough to be measured accurately and showed total sphltings of up to 10 MHz. Their overall structure is shown in fig. 1.
Unfortunately, other absorption lines fell into the regions of these hypertine patterns as indicated in fig. 1. Those hypertine components which coincided accidentally with the additional absorption lines had to be omitted from the fit of the nuclear quadrupole COUpling constants. Looking at a complete listing of tmnsition frequencies with corresponding intensities reveaIs the fact that each absorption line is a superposition of several hyperfine components. The stronger absorption lines correspond to one of the following two possibilities: either the intensity of the strongest hyperfme component of the absorption line is at least five times as large as all the others, or the two strongest hyperfine components have almost equal intensity and are split by only a few kHz. In the former case the strongest, in the latter case the two strongest hyperfine components are assumed to correspond to the measured frequency of the peak absorption. The measured splittings given in table 1 are averages of several measurements. The statistical weight factors for each
442
H. II.
Wenger
et a:.
Nuclear
&adrupole
coupling
connants
of thlonyl
chloride
f;ble I Measured nuclear quadrupole splittings of three ~otalional transitions of SO%l~~ ‘Trahition
,533 -
541
Center
frequency (hlHr)
ComponPnt~)
Quadrupole splhg
06s.
Cd.
F
e
ExpU. weight
18621.112
18627.979
5 5
4 3
1.10 1.10
4
3
6
3
1
2
3.00
1.989
obs.
C-k.
(MHz)
diff.
-4.340
-4.350
0.010
1.80
-4.340 -0.103
-4.344 -0.185
2.40
-0.259
-0.283
1.980
0.004 0.002 0.024 0.009
ajh - aq4
21617.587 -21617.892
8 11 6. 10
4 1 2 2
0.26 0.26 0.26 0.26
-3.114 -2.624 -1.241 1.034
-3.087 -2.586 -1.228 0.970
-0.027 -0.038 -0.013 0.064
954 - 946
24023.905
9 9 12 7
4 3 1 2
0.44 0.44 0.43 0.88
-2.033 -2.033 -1.772 -0.659
-2.063 -2.063 -1.761 -0.725
0.030 0.030 -0.011 0.066
11
2
0.25
0.637
0.587
0.050
24024.207
a) AF= 0 and AE = 0, e numbers Ihe dhTeercnlenergy levels of one F block starting with 1 a1 the-lowest level. measured splitting introduced into the iterative leastsquares fitting procedure were set reciprocally proportional to the standard deviation of the measurement and proportional to the number of measurements. The final results of the least-squares fit are shown in table 2. Transformation of the nuclear quadrupole coupling tensor from the principal inertia axes system to the S-Cl bond axes system depends critically on tie Cl S Cl angle. Hargittai [7] has reported the following molecular structure of thionyl chloride from an electron diffraction study: r (S-Cl) = 2.076 5 0.006 A, r (S-O) = 1.443 +,0.006 A, 4 OSCl = 106.3” * 0.6” and 4 ClSCl = 96.1” + 0.7’. Using these values to Calculate the transformed nuclear quadruple coupling constants, xzz = - 106.0 MHz, xxx = 75.1 MHz and x,,~ = 30.9 MHz were obtained, where the z axis corresponds to the S-Cl bond a&the x axis lies in the Cl-S-Cl plane. Consistent with the uncertainties in the molecular structure, a small shift of 0.8” to a Cl SC1 angle of 96.9” changes the result tOx,=.-95.1 MHz, x, = 64.1 MHz .and x, = 31 .O MHz. This latter result seems to be more in line with the only reference -, to an,S-Cl bbnd, where x,, = - 81 S MHz was found in SF535 Cl [a].
Financial support by the Swiss National Foundation (Project Nrs. 2.82.69 and 2.258.70) is gratefully acknowledged. Table 2
Adjusred nuckar quadrupolc coupling constants with standard enors and rdtational constant& of S03’C12 (in MHz) ‘aa
- 25.01
* 0.07
Ybb
-
f 0.45
0.03
25.04
XCC
A
5086.79
B
2822.55
c
1960.32
DJ DJK
0.001158 -
0.002183
DK
0.006936
61
0.000398
6K
0.001246
a) Ref. (31.
f 0.45
H. U. Wenger er aL. Nuclear quadrupole’couphg a
.
I
I
. ”
n
n
I-
nm
h
PO
c
-
chloride
443
References I.
K gG ’ : :
connants of rhbnyl
:: ‘0
[ 11 C. Joumcl,
Ph. D. thczis, LiUe (1969).
121H.U. Wengcr. Pha. U~esis.ETH Zurich (197d). 131J.L. Destombes. Ph.D. thesis, Lille (1970). 141 J. Bu’tic.J.L. Destombcr. A Dubrulle and G. Joumel. Compt. Rend Aad Sci. (Paxis) 2678 (1968) 48. IS] G. JoumeJ, A. DubruUc. J.L Dcslombes and C. Marli& Compt. Rend Aad Sci. (Paris) 27lB (1970) 331. [6] G.W. Robin and CD. ComweU. J. Chem. whys 21
(1953) 1436. [7] I. Hargiltai, Acts Chim. Hung. 60 (1969) 231. [S] R. Kewley, K.S.R. Murly and TM. Sugden, TEUIS.Fmkty Sot. 56 (1960) 1732.
fig. 1. Calculalcd nuclear quadrupolc multiplcts of the (a) &541,@)836844 and (C)J)s4-946 I0tatiOn~ttTJktions of SO%2. Frequencies are given in MHz. Only hyperfine componenls are assigned wllh F and e wh%hwere used to determine the nuclev quadrupole coupling conslar~ts. Intensity ratios of (a): (b): (c) are I: 2.5: 5.
NORTH-HOLLAND
PUBLISHING
COMPANY
NUCLEARQUADRUPOLECOUPLlNGCONSTANTSOFTHlONYL Luboratory
H.U. WENGER, A. BAUDER and Hs.H. GiiNTHARD Swiss Fedeml Instirute of Technolom, 1X4006
for Physical Chemisrry,
CHLORIDE Zurich. Switrerlond
Received I June 1973 The nuclear qundrupole structure of some low I transitions with large splittings has been measured for thionyl chloride (S03”C12) and analysed in terms of a first order perturbation. The following nuclear quadrupole coupling constants were obtained: 16~ = -25.01 f 0.07 MHz. Xbb = -0.03 i 0.45 hlHz and qc = 25.04 2 0.45 hlHz.
Tbionyl chloride has, even at low frequencies, an extremely rich microwave spectrum as has been pointed out by several authors [l-3]. The low J transitions are comparatively weak. Several isotopic species in nat. unl abundance, complicated nuclear quadrupole splitting patterns originating from two nuclei and excited vibrational states are responsible for this observation. We first failed to directly assign low J transitions on the basis of nuclear quadrupole splittings and Stark effect due to overlapping absorption lines and interfering Stark lobes. Joumel and collaborators [l, 3-51 have given an assignment of R- and Q-branch transitions by systematically investigating the general behaviour of the strongest high J transitions. Only approximate values for the nuclear quadrupole coupling constants were reported [ 11. Medium and high J transitions have been assigned exclusively and their small nuclear hyperfine splittings of around 1 MHz did not warrant a rigorous analysis. In this paper we present the results of the analysis of the nuclear quadrupole splittings of three low J rotational transitions of SO%2. The nuclear quadrupole splitting pattern due to two identical nuclei of a rotational transition is calculated using a first order perturbation treatment in the I,I, IJ F MF representation [6]. The relative intensities of the hyperfine components are obtained by transforming the line strengths in the I, I,IJ FMFscheme with the transformation coefficients which diagonalize the first order perturbation matrices. Following the selection rules AI = 0, + 1 and AF = 0, + 1, the transition frequencies of all possible hyperfine components
with their intensities are calculated. In addition, an actual picture of the nuclear quadrupole multiplet structure is produced by a plotler, assuming lorentzian line shapes of equal line widths for alJ hyperfime components. A description of the computer program for the calculations is given in ref. [2]. Using the Q-branch assignment of Burie et al. [4] and extrapolating it to low J transitions, we were able to identify the three tmnsitions S,, - S4,, 836 - 8, and 9s4 - 9.,6_ They were just strong enough to be measured accurately and showed total sphltings of up to 10 MHz. Their overall structure is shown in fig. 1.
Unfortunately, other absorption lines fell into the regions of these hypertine patterns as indicated in fig. 1. Those hypertine components which coincided accidentally with the additional absorption lines had to be omitted from the fit of the nuclear quadrupole COUpling constants. Looking at a complete listing of tmnsition frequencies with corresponding intensities reveaIs the fact that each absorption line is a superposition of several hyperfine components. The stronger absorption lines correspond to one of the following two possibilities: either the intensity of the strongest hyperfme component of the absorption line is at least five times as large as all the others, or the two strongest hyperfine components have almost equal intensity and are split by only a few kHz. In the former case the strongest, in the latter case the two strongest hyperfine components are assumed to correspond to the measured frequency of the peak absorption. The measured splittings given in table 1 are averages of several measurements. The statistical weight factors for each
442
H. II.
Wenger
et a:.
Nuclear
&adrupole
coupling
connants
of thlonyl
chloride
f;ble I Measured nuclear quadrupole splittings of three ~otalional transitions of SO%l~~ ‘Trahition
,533 -
541
Center
frequency (hlHr)
ComponPnt~)
Quadrupole splhg
06s.
Cd.
F
e
ExpU. weight
18621.112
18627.979
5 5
4 3
1.10 1.10
4
3
6
3
1
2
3.00
1.989
obs.
C-k.
(MHz)
diff.
-4.340
-4.350
0.010
1.80
-4.340 -0.103
-4.344 -0.185
2.40
-0.259
-0.283
1.980
0.004 0.002 0.024 0.009
ajh - aq4
21617.587 -21617.892
8 11 6. 10
4 1 2 2
0.26 0.26 0.26 0.26
-3.114 -2.624 -1.241 1.034
-3.087 -2.586 -1.228 0.970
-0.027 -0.038 -0.013 0.064
954 - 946
24023.905
9 9 12 7
4 3 1 2
0.44 0.44 0.43 0.88
-2.033 -2.033 -1.772 -0.659
-2.063 -2.063 -1.761 -0.725
0.030 0.030 -0.011 0.066
11
2
0.25
0.637
0.587
0.050
24024.207
a) AF= 0 and AE = 0, e numbers Ihe dhTeercnlenergy levels of one F block starting with 1 a1 the-lowest level. measured splitting introduced into the iterative leastsquares fitting procedure were set reciprocally proportional to the standard deviation of the measurement and proportional to the number of measurements. The final results of the least-squares fit are shown in table 2. Transformation of the nuclear quadrupole coupling tensor from the principal inertia axes system to the S-Cl bond axes system depends critically on tie Cl S Cl angle. Hargittai [7] has reported the following molecular structure of thionyl chloride from an electron diffraction study: r (S-Cl) = 2.076 5 0.006 A, r (S-O) = 1.443 +,0.006 A, 4 OSCl = 106.3” * 0.6” and 4 ClSCl = 96.1” + 0.7’. Using these values to Calculate the transformed nuclear quadruple coupling constants, xzz = - 106.0 MHz, xxx = 75.1 MHz and x,,~ = 30.9 MHz were obtained, where the z axis corresponds to the S-Cl bond a&the x axis lies in the Cl-S-Cl plane. Consistent with the uncertainties in the molecular structure, a small shift of 0.8” to a Cl SC1 angle of 96.9” changes the result tOx,=.-95.1 MHz, x, = 64.1 MHz .and x, = 31 .O MHz. This latter result seems to be more in line with the only reference -, to an,S-Cl bbnd, where x,, = - 81 S MHz was found in SF535 Cl [a].
Financial support by the Swiss National Foundation (Project Nrs. 2.82.69 and 2.258.70) is gratefully acknowledged. Table 2
Adjusred nuckar quadrupolc coupling constants with standard enors and rdtational constant& of S03’C12 (in MHz) ‘aa
- 25.01
* 0.07
Ybb
-
f 0.45
0.03
25.04
XCC
A
5086.79
B
2822.55
c
1960.32
DJ DJK
0.001158 -
0.002183
DK
0.006936
61
0.000398
6K
0.001246
a) Ref. (31.
f 0.45
H. U. Wenger er aL. Nuclear quadrupole’couphg a
.
I
I
. ”
n
n
I-
nm
h
PO
c
-
chloride
443
References I.
K gG ’ : :
connants of rhbnyl
:: ‘0
[ 11 C. Joumcl,
Ph. D. thczis, LiUe (1969).
121H.U. Wengcr. Pha. U~esis.ETH Zurich (197d). 131J.L. Destombes. Ph.D. thesis, Lille (1970). 141 J. Bu’tic.J.L. Destombcr. A Dubrulle and G. Joumel. Compt. Rend Aad Sci. (Paxis) 2678 (1968) 48. IS] G. JoumeJ, A. DubruUc. J.L Dcslombes and C. Marli& Compt. Rend Aad Sci. (Paris) 27lB (1970) 331. [6] G.W. Robin and CD. ComweU. J. Chem. whys 21
(1953) 1436. [7] I. Hargiltai, Acts Chim. Hung. 60 (1969) 231. [S] R. Kewley, K.S.R. Murly and TM. Sugden, TEUIS.Fmkty Sot. 56 (1960) 1732.
fig. 1. Calculalcd nuclear quadrupolc multiplcts of the (a) &541,@)836844 and (C)J)s4-946 I0tatiOn~ttTJktions of SO%2. Frequencies are given in MHz. Only hyperfine componenls are assigned wllh F and e wh%hwere used to determine the nuclev quadrupole coupling conslar~ts. Intensity ratios of (a): (b): (c) are I: 2.5: 5.