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Vapour state Raman spectra and thermodynamic properties of sulphur dichloride and disulphur dichloride
Spectrochimica Acta, Vol. 81A, pp. 161 to 167. Pergamon Press 1975. Printed in Northern Ireland
Vapour state Raman spectra and thermodynamic properties of sulphur dichloride and disulphur dichloride S. G. F ~ = ~ s
and D. J. H~_~P~SO~
Division of Chemical Standards, National Physical Laboratory, Teddington, TWll 0LW, England (Received 23 February 1974)
Abstract---Vapour state Raman spectra with polarization data are reported for sulphur dichloride and disulphur dichloride. A heated Raman vapour cell for use over the temperature range 300-700 K is described. Complete vibrational assignments for sulphur dichloride and disulphur dichloride in the vapour state are given, along with their ideal gas state thermodyvamio properties over the temperature range 273-15-1500 K. ~NTRODUCTION _ALTHOUGH the R a m a n spectra of sulphur dichloride (SCI~) [1, 2] and disulphur dichloride (S~CI~) [3-7] in the liquid state have been measured by several authors, no vapour state R a m a n data have been reported. Vapour state i.r. spectra ot~ SCI~ [2, 8, 9] and S~CI~ [7] have been measured, but u n c e r t a i n t y remains about the values of the vibrational wavenumbers of the two higher fundamentals in SCI~ [2] and two low-lying fundamentals in S~CI~ [7] in the vapour state. The R a m a n spectra of SCI~ and S~CI~ in the vapour state have therefore been measured to complete the vibrational assignments for use in the calculation of their thermodynamic properties. E a r l y calculations of the ideal gas state t h e r m o d y n a m i c functions of SCI~ [10] and S~CI~ [11] used inaccurate vibrational assignments. More recent calculations for SCI~ [12-14] and S~CI~ [5, 13-16], which used liquid state values for the f u n d a m e n t a l wavenumbers and structural d a t a determined from early electron [1~ H. STAM~a~cH, R. FOttNE~S and K. So~E, J. Chem. Phys. 23, 972 (1955). [2] R. SAVOIEand J. TREMBLY, Canad. J. S~ec~osc. 17, 73 (1972). [3] H. G~RDI~Gand R. W~sT~x, Rec. Tray. Chim. 60, 702 (1941). [4] H. ST~rMREIC~and R. Fo~r~P.IS, S~e~roehim. ~lc~ 8, 46 (1956). [5] E. B. BP,~uI~y, M. S. MA1"nv~and C. A. F~E~ZEL,J. Chem. Phys. 47, 4325 (1967). [6] P. J. HEND~ and P. J. I). PA~, J. Che~. Soc. (~4), 908 (1968). [7] S. G. F ~ r s x s s , J. MoL Stru~re 2, 271 (1968). [8~ G. M. BARROW,J. Phys. Chem. 59, 987 (1955). [9] Y. MORI~O, Y. MUP~TA, T. ITO and J. N A ~ r A ~ , J. Phys. Soc. J a ~ n 17, 37 (1962). [10~ C. A. McDow~T.r.and E. A. MoET.wY~-HuaH~s,Proe. Roy. Soc. (Lo~on) 187A, 398 (1946). [11] N. W. L u ~ and K. H. Tovnu~r~R, J. Chem. Phys. 21, 2225 (1953). [12] G. N A G ~ J ~ , BUlLSoc. Chin. Be~g. 72, 16 (1962). [13] H. MAc~rT.~. and P. A. G. O ' H A ~ , ~'a~s. Faraday ~oc. §9, 309 (1963). [14] B. J. McBriDe., S. H ~ . ~ J. G. ]~n~,~.Rsand S. Go~uoN, ~hermodynam~ ~orolve~/e~to 6000 K for 210 s~bstances involvi~ ~hefirs~ 18 elements, NASA 8P-8001 (1963). [15] K. K. l~r.~.~.y and E. G. K~No, ~ureau of Mines Bull. 592 (1961). [16] K. R A ~ w A ~ r and S. JAYA~M~, .Aet~ Phys. P o ~ . A40, 883 (1971), 161
162
s . G . F~tA~rKISS and D. J. HAm~ISON
diffraction measurements [17-20], require correction following recent structure determinations [21, 22] and the vapour state R a m a n data reported here. Most of the previous calculations for $2C1~ contain additional errors t h a t require correction. Three calculations [13-15] failed to consider the difference in optical activity of the two rotamers of $2C1~, while a fourth calculation [5] is so substantially in error t h a t its basis is not clear. A fifth calculation [16] failed to consider the optical activity of the rotamers and the rotational s y m m e t r y of $2C12, b u t since these two errors cancel one another, it provides the most accurate of the reported ideal gas state thermodynamic functions of S ~C12. EXPERIMEIWTAL
Samples of sulphur dichloride (SCI~) and disulphur dichloride (S~Cl~) were purified b y fractional distillation. No impurities were observed from the R a m a n spectrum of disuiphur dichloride, b u t small amounts of chlorine and disulphur dichloride were observed in the sample of sulphur dichloride, which dissociates according to the reaction [23]: 2SC1~ ---- S~CI~ -~ C12. R a m a n spectra were recorded using a Spex 1401 spectrophotometer with an E R - 3 detection and recording system. Excitation b y 488.0 and 514.5 nm radiation (1.5 W) was obtained from an ionised argon laser (Coherent Radiation 52 B). A 90 ° excitation collection geometry was used, with space co-ordinates defined such t h a t the laser was propagated along the z axis and polarized parallel to the y axis, and the axis of observation was along the x axis. A spike filter was situated between the laser and the sample to reduce the intensity of non-lasing radiation, and a quartz wedge scrambler was located between the sample and the spectrophotometer to depolarize scattered radiation entering the instrument. Depolarization measurements were made b y rotation (about the x axis) of a polarization analyzer placed between the sample and the quartz wedge. Specimens were held in P y r e x cells in a pyrophyllite furnace (shown in Figs. 1 and 2) which was mounted on an adjustable kinematic platform. The cells were made from glass tubing of 11 mm diameter, consisting of a horizontal section attached to a vertical limb which served as a reservoir for non-volatilized liquid or solid admitted through a restriction subsequently sealed off i n vacuo. The cell was surrounded b y the furnace which was made in two parts each heated b y separate coils of 26 gauge Nichrome wire wound on pyrophyllite formers. Temperature control to ± 1 K was achieved b y use of two proportional temperature controllers (Eurotherm Models 020 and 021 for thermoeouple inputs) with the temperature of the horizontal section of the cell maintained at a b o u t 10 K above t h a t of the reservoir to minimise the possibility of observing R a m a n scattering [17] K. J. PALMER,J . Amer. Chem. •oc. 60, 2360 (1938). [18] D. P. STEVENSON and J. Y. BEACH, J. Amer. Chem. Soe. 60, 2872 (1938). [19] P. G. ACKE~-~ and J. E. MA~It, J . Chem. _Phys. 4, 377 (1936). [20] E. I-IXROTA,B u l l Chem. Soc. Japan 31, 130 (1958).
[21] T. L. WF.Az.~R~.Y, unpublished results quoted in [2]. [22] B. BEAGLEY,G. H. ECKERSLEY,D. P. BRow~ and D. ToMLr~soN, Trans. Faraday Soc. 65, 2300 (1969). [231 A. H. SPoNa, J. Chem. Sot., 1283 (1934).
Vapour s~ate Raman spectra of sulphur dichloride and disulphur dichloride
Fig. 1. Sectional view in
yz
163
plane of Raman vapour cell and furnace.
Fig. 2. Sectional view in x z plane of Raman vapour cell and furnace. from the specimen in its condensed states. The sample temperature of the vapour near the reservoir was measured and controlled b y use of two thermocouples (A and B, as shown in Fig. 1) held in contact with the vertical limb of the cell through horizontal holes, while the temperature of the vapour in the R a m a n excitation zone was measured from a thermocouple (C, as shown in Fig. 2) located in a horizontal hole adjacent to the horizontal section of the cell. F r o m preliminary experiments, the absolute temperature of the vapour in the R a m a n excitation zone was observed to differ by not more t h a n 0.5~o from the temperature at thermocouple C over the temperature range (300-700 K) of the furnace. Vertical holes in the furnace allowed the laser radiation to pass through the vapour in the horizontal section of the cell. R a m a n radiation was collection through a conical hole of 30 ° inclusive angle having a horizontal axis and focused into the monochromator, the aperture of the hole being just sufficient to prevent vignetting of the radiation received by the f/1.6 collecting lens. The vertical and conical holes
164
S. G. F~a~r~iss and D. J. H~m~soN
were sealed b y P y r e x discs to reduce t he loss of heat from t he cell. Inside walls o f t h e furnace near t he conical holes were coated with black (Ebonide) lacquer to reduce th e a m o u n t of scattered light f r om t he cell walls entering the monochromator.
RAMAN SPECTRA AND VIBRATIONAL ASSIGNMENTS The R a m a n spectrum of SCI z v a p o u r a t 335 K consisted of two m edi um i n t e ns ity bands at 205 cm -1 (0.2) a nd 528 cm -1 (0.0), where t h e values in parentheses are depolarization ratios. Since SCI~ has Cso s y m m e t r y [17, 18] with two a 1 and one b~ f u n dam e nt a l s [24] t h e two R a m a n bands are readily assigned t o t he two al f u n d amen ta l s ~1 and ~2. T he t h i r d f u n d a m e n t a l ~s, which was n o t observed in t he R a m a n spectrum, is expected to be near ~1. I n this region i.r. b a n d m a x i m a a t 520, 525 and 530 cm -1 have been r e por t ed [2]. Although the i.r. band contours of ~1 and ~ are complicated b y m u t u a l overlap, ~1 is assigned t o t he m axi m a at 520 an d 530 cm -1 since it is expected to have a t y p e B b a n d contour with a P - R separation of a b o u t 13 cm -1 [25]. The ant i s ymm et ri e SC1 stretch ~s should have a t y p e -4 b a n d contour with a P - R separation of about 15 cm -1 [25], and although its P an d R branches are obscured b y ~1 t he central Q branch of ~3 is assigned to t h e i.r. b a n d at 525 cm -~. Thus t he vibrational assignment of SCl~ v a p o u r is: (a~): 528, 205; (b~): 525 cm -1. Th e R a m a n spectrum of S~CI~ v a p o u r at 405 K is summarized in Table 1 and illustrated in Fig. 3, where I~, and I,~ are t he R a m a n signals with t he analyzer polarized parallel t o t he y and z axes respectively. Since S~CI~ has C2 s y m m e t r y [19, 20, 22] with four @and two b fundamentals, t he three strong, polarized R a m a n bands at 92, 202 and 466 cm -~ are a fundamentals, while t he depolarized R a m a n bands at 240 and 457 cm -~ are t he b fundamentals. T he fourt h @ f u n d a m e n t a l was n o t observed in t he R a m a n s pect r um o f t he vapour, b u t on the basis of previous measurements of the i.r. spectrum of the v a p o u r [7] and t he R a m a n Table 1. Raman and i.r. spectra of SsC1s vapour Raman
Infrared [7]
A~/cm-1
I
p
78 85 92 202 240
w w s s w
0.2 0.1 dp
457 466
m,sh s
dp 0.1
~/em-1
I
95 210 244 452 461
vvw? vvw? w s } vs
546
w
Assignment Vl -- ~2 ~1 -- ~5 ~4 ~8 ve vs ~2 v1
s, m, w ~ strong, medium, weak; v = very; sh = shoulder; d p = apparently depolarized. [24] R. S. 1KuT~g_~, J. Ghem. Phys. 23, 1997 (1955). [25] T. UEDA and T. Sm~A~OUCIII, J. Mol. Sypec~ 28, 350 (1968).
Vapour state Raman spectra of sulphur dichloride and disulphur dichloride
165
466
2O2
Ramon signal
I
600
I
500
I
400
I
T
300 Ramon shifts
200
I
I00
I
0
Av ( c ~ ' )
Fig. 3. Raman spectrum of S=C]= vapour at 405 K in range Av = 0-600 cm-z using 488-0 nm excitation. spectrum of the liquid [3-7] it is assigned to 546 cm -z. The present vibrational assignment is consistent with previous assignments for the liquid [3-7, 26], and in conjunction with the previously reported i.r. spectrum of the vapour [7] provides the following values for the fundamental wavenumbers of S=CI= vapour--(a): 546, 466, 202, 92; (b): 461,244 cm -t. THERMODYNAMIC PROPERTIES Ideal gas state t h e r m o d y n a m i c functions were determined using values of the f u n d a m e n t a l constants [27] and relative atomic masses (S = 32.06; C1 = 35.453) [28] recommended by IUPAC. The structure of SCI= was t a k e n to be: r(S--C1) = 0.2014 n m and A(CI--S--C1)----102.8 ° [2], which gives the value 5.898 × 10-1t~ gS cm e for the product of the three principal moments of inertia. The recent electron diffraction s t u d y of S~CI~ [22] has given the following structure: r(S--C1) = 0.2057 nm, r ( S - - S ) = 0.1931 nm, A ( C 1 - - S - - S ) = 108.2 ° and the dihedral angle (~b) between the two S--C1 planes is 84.8 °, from which the product of the three principal moments of inertia and the reduced moment of inertia of the SC1 group were calculated [29] to be 6.360 × 10-118g 3 cm 6 and 5-487 × 10-Sgg cm 2, respectively. The s y m m e t r y numbers for overall rotation of [26] [27] [28] [29]
H. 5. B~a~s~i~ and J. PowI~O, J. Chem. Phys. 18, 1018 (1950). F. D. Rossr~, Pure A ~ d Chem. 9, 453 (1964). At~mic We~ght~ of the Elements, Pure A1wl~ Chem. 30, 637 (1972). J. E. KILPA~.ICKand K. S. PfiZER, J. Chem. Phys. 17, 1064 (1949).
166
S.G.
FRANKISS a n d D. J. H A m ~ S O N
|
-I--
o
IF +-
v
~t
O
I
r~
O
o
AT
o
7
o O
~o O ¢J ¢S
'r,
J~
O A
A
x
X
ii °
~7
I? v~
I
~ooo~ o o o ~ I
Vapour state Raman spectra of sulphur dichloride and disulphur dichloride
167
SCI~ and $2C12, are both 2. Thermodynamic properties of SCI~ and $2C12 were calculated assuming the rigid rotor, harmonic oscillator approximation and using the following values for the fundamentals of SC12 (528, 205 and 525 cm -1) and S~CI~ (546, 466, 202, 461 and 244 cm-1). Contributions from internal rotation in S~C1z were calculated from a modified classical approximation [30] by appropriate integration of the internal rotation potential function from ¢ ---- 0 to ~b = 27r, to allow for the difference in optical activity of the two rotamers. A potential function of the form V = V 0 -- Z.(V~/2)(1 -- cos n~b) was used, for which the terms Vo = 50.18, Ira---- --46.85 and V,---- --5.85 k J mo1-1 were determined from the wavenumber of the torsion (92 cm-1), the dihedral angle of the rotamers (84.8 °) and by assuming t h a t V1, V4 and higher terms are zero. Chemical t h e r m o d y n a m i c properties of sulphur dichloride and disulphur dichloride in the ideal gas state over the temperature range 273.15-1500 K are given in Tables 2 and 3, respectively. The standard enthalpy and Gibbs energy of formation and logarithm of the standard equilibrium constant of formation of SCI~ and S~C12 in the ideal gas state are also given in Tables 2 and 3, and were calculated from values of the enthalpy and entropy of chlorine and sulphur in their reference states [31] and from the values --22.6 and --17.2 k J tool -1 for the enthalpy of formation at 298.15 K of SC12(g) and S2C12(g), respectively [32]. The reference states of sulphur are taken to be rhombic crystalline sulphur for temperatures 273.15-368.54 K, monoelinic crystalline sulphur for temperatures 368.54-388.36 K, liquid sulphur for temperatures 388.36-717.75 K and diatomic sulphur in the ideal gas state for temperatures 717.75-1500 K. The reference state of chlorine for temperatures 273.15-1500 K is taken to be diatomic chlorine in the ideal gas state. [30] S. G. FRANKISS,J. Chem. Soc. Faraday Trans. II 70, 1516 (1974). [31] JA_NAF Thermochemical Tables 2rid (Edn.) NSRD4NBS 87, (1971). [32J K. C. MILLS,Selected Thermodynamic Data for Inorganic Sulphides, Selenides and Tellurides. Butterworths, London (1974).
Vapour state Raman spectra and thermodynamic properties of sulphur dichloride and disulphur dichloride S. G. F ~ = ~ s
and D. J. H~_~P~SO~
Division of Chemical Standards, National Physical Laboratory, Teddington, TWll 0LW, England (Received 23 February 1974)
Abstract---Vapour state Raman spectra with polarization data are reported for sulphur dichloride and disulphur dichloride. A heated Raman vapour cell for use over the temperature range 300-700 K is described. Complete vibrational assignments for sulphur dichloride and disulphur dichloride in the vapour state are given, along with their ideal gas state thermodyvamio properties over the temperature range 273-15-1500 K. ~NTRODUCTION _ALTHOUGH the R a m a n spectra of sulphur dichloride (SCI~) [1, 2] and disulphur dichloride (S~CI~) [3-7] in the liquid state have been measured by several authors, no vapour state R a m a n data have been reported. Vapour state i.r. spectra ot~ SCI~ [2, 8, 9] and S~CI~ [7] have been measured, but u n c e r t a i n t y remains about the values of the vibrational wavenumbers of the two higher fundamentals in SCI~ [2] and two low-lying fundamentals in S~CI~ [7] in the vapour state. The R a m a n spectra of SCI~ and S~CI~ in the vapour state have therefore been measured to complete the vibrational assignments for use in the calculation of their thermodynamic properties. E a r l y calculations of the ideal gas state t h e r m o d y n a m i c functions of SCI~ [10] and S~CI~ [11] used inaccurate vibrational assignments. More recent calculations for SCI~ [12-14] and S~CI~ [5, 13-16], which used liquid state values for the f u n d a m e n t a l wavenumbers and structural d a t a determined from early electron [1~ H. STAM~a~cH, R. FOttNE~S and K. So~E, J. Chem. Phys. 23, 972 (1955). [2] R. SAVOIEand J. TREMBLY, Canad. J. S~ec~osc. 17, 73 (1972). [3] H. G~RDI~Gand R. W~sT~x, Rec. Tray. Chim. 60, 702 (1941). [4] H. ST~rMREIC~and R. Fo~r~P.IS, S~e~roehim. ~lc~ 8, 46 (1956). [5] E. B. BP,~uI~y, M. S. MA1"nv~and C. A. F~E~ZEL,J. Chem. Phys. 47, 4325 (1967). [6] P. J. HEND~ and P. J. I). PA~, J. Che~. Soc. (~4), 908 (1968). [7] S. G. F ~ r s x s s , J. MoL Stru~re 2, 271 (1968). [8~ G. M. BARROW,J. Phys. Chem. 59, 987 (1955). [9] Y. MORI~O, Y. MUP~TA, T. ITO and J. N A ~ r A ~ , J. Phys. Soc. J a ~ n 17, 37 (1962). [10~ C. A. McDow~T.r.and E. A. MoET.wY~-HuaH~s,Proe. Roy. Soc. (Lo~on) 187A, 398 (1946). [11] N. W. L u ~ and K. H. Tovnu~r~R, J. Chem. Phys. 21, 2225 (1953). [12] G. N A G ~ J ~ , BUlLSoc. Chin. Be~g. 72, 16 (1962). [13] H. MAc~rT.~. and P. A. G. O ' H A ~ , ~'a~s. Faraday ~oc. §9, 309 (1963). [14] B. J. McBriDe., S. H ~ . ~ J. G. ]~n~,~.Rsand S. Go~uoN, ~hermodynam~ ~orolve~/e~to 6000 K for 210 s~bstances involvi~ ~hefirs~ 18 elements, NASA 8P-8001 (1963). [15] K. K. l~r.~.~.y and E. G. K~No, ~ureau of Mines Bull. 592 (1961). [16] K. R A ~ w A ~ r and S. JAYA~M~, .Aet~ Phys. P o ~ . A40, 883 (1971), 161
162
s . G . F~tA~rKISS and D. J. HAm~ISON
diffraction measurements [17-20], require correction following recent structure determinations [21, 22] and the vapour state R a m a n data reported here. Most of the previous calculations for $2C1~ contain additional errors t h a t require correction. Three calculations [13-15] failed to consider the difference in optical activity of the two rotamers of $2C1~, while a fourth calculation [5] is so substantially in error t h a t its basis is not clear. A fifth calculation [16] failed to consider the optical activity of the rotamers and the rotational s y m m e t r y of $2C12, b u t since these two errors cancel one another, it provides the most accurate of the reported ideal gas state thermodynamic functions of S ~C12. EXPERIMEIWTAL
Samples of sulphur dichloride (SCI~) and disulphur dichloride (S~Cl~) were purified b y fractional distillation. No impurities were observed from the R a m a n spectrum of disuiphur dichloride, b u t small amounts of chlorine and disulphur dichloride were observed in the sample of sulphur dichloride, which dissociates according to the reaction [23]: 2SC1~ ---- S~CI~ -~ C12. R a m a n spectra were recorded using a Spex 1401 spectrophotometer with an E R - 3 detection and recording system. Excitation b y 488.0 and 514.5 nm radiation (1.5 W) was obtained from an ionised argon laser (Coherent Radiation 52 B). A 90 ° excitation collection geometry was used, with space co-ordinates defined such t h a t the laser was propagated along the z axis and polarized parallel to the y axis, and the axis of observation was along the x axis. A spike filter was situated between the laser and the sample to reduce the intensity of non-lasing radiation, and a quartz wedge scrambler was located between the sample and the spectrophotometer to depolarize scattered radiation entering the instrument. Depolarization measurements were made b y rotation (about the x axis) of a polarization analyzer placed between the sample and the quartz wedge. Specimens were held in P y r e x cells in a pyrophyllite furnace (shown in Figs. 1 and 2) which was mounted on an adjustable kinematic platform. The cells were made from glass tubing of 11 mm diameter, consisting of a horizontal section attached to a vertical limb which served as a reservoir for non-volatilized liquid or solid admitted through a restriction subsequently sealed off i n vacuo. The cell was surrounded b y the furnace which was made in two parts each heated b y separate coils of 26 gauge Nichrome wire wound on pyrophyllite formers. Temperature control to ± 1 K was achieved b y use of two proportional temperature controllers (Eurotherm Models 020 and 021 for thermoeouple inputs) with the temperature of the horizontal section of the cell maintained at a b o u t 10 K above t h a t of the reservoir to minimise the possibility of observing R a m a n scattering [17] K. J. PALMER,J . Amer. Chem. •oc. 60, 2360 (1938). [18] D. P. STEVENSON and J. Y. BEACH, J. Amer. Chem. Soe. 60, 2872 (1938). [19] P. G. ACKE~-~ and J. E. MA~It, J . Chem. _Phys. 4, 377 (1936). [20] E. I-IXROTA,B u l l Chem. Soc. Japan 31, 130 (1958).
[21] T. L. WF.Az.~R~.Y, unpublished results quoted in [2]. [22] B. BEAGLEY,G. H. ECKERSLEY,D. P. BRow~ and D. ToMLr~soN, Trans. Faraday Soc. 65, 2300 (1969). [231 A. H. SPoNa, J. Chem. Sot., 1283 (1934).
Vapour s~ate Raman spectra of sulphur dichloride and disulphur dichloride
Fig. 1. Sectional view in
yz
163
plane of Raman vapour cell and furnace.
Fig. 2. Sectional view in x z plane of Raman vapour cell and furnace. from the specimen in its condensed states. The sample temperature of the vapour near the reservoir was measured and controlled b y use of two thermocouples (A and B, as shown in Fig. 1) held in contact with the vertical limb of the cell through horizontal holes, while the temperature of the vapour in the R a m a n excitation zone was measured from a thermocouple (C, as shown in Fig. 2) located in a horizontal hole adjacent to the horizontal section of the cell. F r o m preliminary experiments, the absolute temperature of the vapour in the R a m a n excitation zone was observed to differ by not more t h a n 0.5~o from the temperature at thermocouple C over the temperature range (300-700 K) of the furnace. Vertical holes in the furnace allowed the laser radiation to pass through the vapour in the horizontal section of the cell. R a m a n radiation was collection through a conical hole of 30 ° inclusive angle having a horizontal axis and focused into the monochromator, the aperture of the hole being just sufficient to prevent vignetting of the radiation received by the f/1.6 collecting lens. The vertical and conical holes
164
S. G. F~a~r~iss and D. J. H~m~soN
were sealed b y P y r e x discs to reduce t he loss of heat from t he cell. Inside walls o f t h e furnace near t he conical holes were coated with black (Ebonide) lacquer to reduce th e a m o u n t of scattered light f r om t he cell walls entering the monochromator.
RAMAN SPECTRA AND VIBRATIONAL ASSIGNMENTS The R a m a n spectrum of SCI z v a p o u r a t 335 K consisted of two m edi um i n t e ns ity bands at 205 cm -1 (0.2) a nd 528 cm -1 (0.0), where t h e values in parentheses are depolarization ratios. Since SCI~ has Cso s y m m e t r y [17, 18] with two a 1 and one b~ f u n dam e nt a l s [24] t h e two R a m a n bands are readily assigned t o t he two al f u n d amen ta l s ~1 and ~2. T he t h i r d f u n d a m e n t a l ~s, which was n o t observed in t he R a m a n spectrum, is expected to be near ~1. I n this region i.r. b a n d m a x i m a a t 520, 525 and 530 cm -1 have been r e por t ed [2]. Although the i.r. band contours of ~1 and ~ are complicated b y m u t u a l overlap, ~1 is assigned t o t he m axi m a at 520 an d 530 cm -1 since it is expected to have a t y p e B b a n d contour with a P - R separation of a b o u t 13 cm -1 [25]. The ant i s ymm et ri e SC1 stretch ~s should have a t y p e -4 b a n d contour with a P - R separation of about 15 cm -1 [25], and although its P an d R branches are obscured b y ~1 t he central Q branch of ~3 is assigned to t h e i.r. b a n d at 525 cm -~. Thus t he vibrational assignment of SCl~ v a p o u r is: (a~): 528, 205; (b~): 525 cm -1. Th e R a m a n spectrum of S~CI~ v a p o u r at 405 K is summarized in Table 1 and illustrated in Fig. 3, where I~, and I,~ are t he R a m a n signals with t he analyzer polarized parallel t o t he y and z axes respectively. Since S~CI~ has C2 s y m m e t r y [19, 20, 22] with four @and two b fundamentals, t he three strong, polarized R a m a n bands at 92, 202 and 466 cm -~ are a fundamentals, while t he depolarized R a m a n bands at 240 and 457 cm -~ are t he b fundamentals. T he fourt h @ f u n d a m e n t a l was n o t observed in t he R a m a n s pect r um o f t he vapour, b u t on the basis of previous measurements of the i.r. spectrum of the v a p o u r [7] and t he R a m a n Table 1. Raman and i.r. spectra of SsC1s vapour Raman
Infrared [7]
A~/cm-1
I
p
78 85 92 202 240
w w s s w
0.2 0.1 dp
457 466
m,sh s
dp 0.1
~/em-1
I
95 210 244 452 461
vvw? vvw? w s } vs
546
w
Assignment Vl -- ~2 ~1 -- ~5 ~4 ~8 ve vs ~2 v1
s, m, w ~ strong, medium, weak; v = very; sh = shoulder; d p = apparently depolarized. [24] R. S. 1KuT~g_~, J. Ghem. Phys. 23, 1997 (1955). [25] T. UEDA and T. Sm~A~OUCIII, J. Mol. Sypec~ 28, 350 (1968).
Vapour state Raman spectra of sulphur dichloride and disulphur dichloride
165
466
2O2
Ramon signal
I
600
I
500
I
400
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200
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Fig. 3. Raman spectrum of S=C]= vapour at 405 K in range Av = 0-600 cm-z using 488-0 nm excitation. spectrum of the liquid [3-7] it is assigned to 546 cm -z. The present vibrational assignment is consistent with previous assignments for the liquid [3-7, 26], and in conjunction with the previously reported i.r. spectrum of the vapour [7] provides the following values for the fundamental wavenumbers of S=CI= vapour--(a): 546, 466, 202, 92; (b): 461,244 cm -t. THERMODYNAMIC PROPERTIES Ideal gas state t h e r m o d y n a m i c functions were determined using values of the f u n d a m e n t a l constants [27] and relative atomic masses (S = 32.06; C1 = 35.453) [28] recommended by IUPAC. The structure of SCI= was t a k e n to be: r(S--C1) = 0.2014 n m and A(CI--S--C1)----102.8 ° [2], which gives the value 5.898 × 10-1t~ gS cm e for the product of the three principal moments of inertia. The recent electron diffraction s t u d y of S~CI~ [22] has given the following structure: r(S--C1) = 0.2057 nm, r ( S - - S ) = 0.1931 nm, A ( C 1 - - S - - S ) = 108.2 ° and the dihedral angle (~b) between the two S--C1 planes is 84.8 °, from which the product of the three principal moments of inertia and the reduced moment of inertia of the SC1 group were calculated [29] to be 6.360 × 10-118g 3 cm 6 and 5-487 × 10-Sgg cm 2, respectively. The s y m m e t r y numbers for overall rotation of [26] [27] [28] [29]
H. 5. B~a~s~i~ and J. PowI~O, J. Chem. Phys. 18, 1018 (1950). F. D. Rossr~, Pure A ~ d Chem. 9, 453 (1964). At~mic We~ght~ of the Elements, Pure A1wl~ Chem. 30, 637 (1972). J. E. KILPA~.ICKand K. S. PfiZER, J. Chem. Phys. 17, 1064 (1949).
166
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Vapour state Raman spectra of sulphur dichloride and disulphur dichloride
167
SCI~ and $2C12, are both 2. Thermodynamic properties of SCI~ and $2C12 were calculated assuming the rigid rotor, harmonic oscillator approximation and using the following values for the fundamentals of SC12 (528, 205 and 525 cm -1) and S~CI~ (546, 466, 202, 461 and 244 cm-1). Contributions from internal rotation in S~C1z were calculated from a modified classical approximation [30] by appropriate integration of the internal rotation potential function from ¢ ---- 0 to ~b = 27r, to allow for the difference in optical activity of the two rotamers. A potential function of the form V = V 0 -- Z.(V~/2)(1 -- cos n~b) was used, for which the terms Vo = 50.18, Ira---- --46.85 and V,---- --5.85 k J mo1-1 were determined from the wavenumber of the torsion (92 cm-1), the dihedral angle of the rotamers (84.8 °) and by assuming t h a t V1, V4 and higher terms are zero. Chemical t h e r m o d y n a m i c properties of sulphur dichloride and disulphur dichloride in the ideal gas state over the temperature range 273.15-1500 K are given in Tables 2 and 3, respectively. The standard enthalpy and Gibbs energy of formation and logarithm of the standard equilibrium constant of formation of SCI~ and S~C12 in the ideal gas state are also given in Tables 2 and 3, and were calculated from values of the enthalpy and entropy of chlorine and sulphur in their reference states [31] and from the values --22.6 and --17.2 k J tool -1 for the enthalpy of formation at 298.15 K of SC12(g) and S2C12(g), respectively [32]. The reference states of sulphur are taken to be rhombic crystalline sulphur for temperatures 273.15-368.54 K, monoelinic crystalline sulphur for temperatures 368.54-388.36 K, liquid sulphur for temperatures 388.36-717.75 K and diatomic sulphur in the ideal gas state for temperatures 717.75-1500 K. The reference state of chlorine for temperatures 273.15-1500 K is taken to be diatomic chlorine in the ideal gas state. [30] S. G. FRANKISS,J. Chem. Soc. Faraday Trans. II 70, 1516 (1974). [31] JA_NAF Thermochemical Tables 2rid (Edn.) NSRD4NBS 87, (1971). [32J K. C. MILLS,Selected Thermodynamic Data for Inorganic Sulphides, Selenides and Tellurides. Butterworths, London (1974).