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Electric dichroism spectroscopy in the vacuum ultraviolet dimethylsulfide and thiiran
CHEUICAL PHYSICS LE3-TERS
Volume 77. number 1
ELECTRIC
DICHROISM
1 Jarmar>
1981
SPECTROSCOPY IN THE VACUUM ULTRAVIOLET
DIMETHYLSULFIDE
AND THIIRAN
Dame1 D ALTENLOH
and B R. RUSSELL
Deparitnerit ojCI~er?~~srr)~ Xorth Teras Srare Utrtt erstry, Detrro~~, Teros 76-703 L/SA Kecened 6 August 1980. III final form 8 October 1980
Eleculc field techmques have been used to mvesugate certam s, p and d Rydberg absorpuon bands for dunethylsulfide (DXIS) and ethylene sulfide (thurnne) wth respect to the polarlzatIon of the translhons, the &pole moment, nod mean polar-
~znbht~ changes that occur upon
cxcnatlon
A techruque using Intense electric Gelds, electnc lmear &chroism (ELD) ha been developed and dcscribed m previous amcles and used to obtain certam ekcned-state propertles [14] These parameters are the change m dipole moment between the ground and evclted states, the corresponding changes m polarizablhcy. and the angle between the electnc dipole transltlon rnornent and the change m &pole moment between the two states (polarlzatlon of the transition). These parameters are used to help charactenze electronic states for certam absorptlons for dunethylsulfide (DMS) and thhrane (ethylene sulfide) The absorptlons Investigated are the 2122 A band of thurane and the 2284 a band of DMS, the 1922a band of thurane and the 19598 band of DMS, and the 1740A band of thurane previously rdentlfied as the 4s -II, 4p +-II, 3d + iz Rydberg cransltlons, respectively [5,6] (table
I)nese two dlvalent sulfur compounds are the slmplest of two classes, the symmetnc straight-cham atkyl sulfides and the cychc sulfides. The basic difference between these two classes of compounds IS the bresence of the ring. Assuming that the geometries reman unchanged upon excltatlon for these compounds, then excited-state properties with respect to the structural restnctlons of the ring can be inferred from the results of the electnc-field data. The vacuum ultravioIet
at dlstmgulslung the Rydberg from the non-Rydberg for senes of sulfur compounds. They noted that the energes of Rydberg absorption bands appeared to “line up” when the ionization potenmls were ahgned. Robln [6] presented extensive arguments based on term values and sunddntles with the oxygen analogs to assign the absorptlons to be discussed. These pre-
rlbsorptlons
vlous assignnlents
were in apparent
contrackclon
to
those of Basco and Morse [7]. The results obtained from the electric-field studies are consistent with the assignments of Clark and Simpson and Robin Vapor-phase spectra for timethylsulfide and thurane were obtamed with apparatus wiuch has been described prevrously [ 1 _I] _Certam modlficatlons have been made to Interface wrth a microprocessor (Apple II+). The ELD signal was obtamed by locking-m on the fundamental of the ac fields. Thus slgnal IS four times as Intense as the overtone used prewously Examples of the ELD and absorption spectra for the s, p and d Rydberg bands for thurane are gven in figs. 1-3. Slmllar spectra for the s and p Rydberg bands for DMS were obtamed but are not shown Analysts of these spectral data IS accomphshed by a least-squares fit to the theoretical expression below [ i,3]. The theoretlcal denvation of tlus equation as well as the manner the data 1s treated to obtam certam excited-state parameters has been described [ 11.
217
TiIble 1 ~ornp~a~on of data for ~rne~~~ut~de znd thmanc a) ~_ ~_I______ ____-__ ---__ --lon=rltion
-
-__
______Dimethyl sulfide
-
term value (cm-‘)
72891
4sAk 4PBI 3dAI
43870 5116.5 56290
47 125
s
26500
26000 21000 SO00
II
52029 5749 1
19100 13800
IlP rid
1 5Oc-0.01
ground-srate &pole moment (D) me.m polxrlzsbdtty ( k3)
c-s
4 73
1 802
1 819 1492
98” 52’
65” 48
C-C
bond an&e
c-s-c
1.5x lo-’
4SA, ~PBI 3dA1
1.65+0 01
33
7
bond length (Sr)
-Thurime
70092
potentul (cm-’ )
transxtronenergy (cm-‘)
ground-state
J.Januxy 1981
CHEMICAL PHYSICS LETTERS
Volume 77, number 1
2 2x 10-3
4 8x 1O-3 1.9x 10-z 1.2x10-
n) Data obtaned from refs [6 13-17)
6-O
45
(1)
30
VO % ;;
I.5
where Go, Z,I 1s the energy regon for the absorption band (cm- 1); A"(Z),dAo(~)~d~ and d2A0(3)fdZ2 are the absorption profile and the correspondmg first and second derivatives, -f,/f O(E) IS the electrtc field
S 00 25
SIgnal.
The results of the least-squares fit are given m table 2 for the coefficw&s C, , CT,, and C, for the absorptions studed. The coeffictents C, and C2 represent terms mvokng ground- and excited-state quantities. These quantities include the &pole moment and mean 4
WAVELENGTH
(nm 1
Fig 1. Examples of the absorption (r1O), unpolarized h&t elecuochrom~m (-fpn/io) and 90” polarized hght electrochiomism (-Iz”/lo) spectra for the 2122 II band of tbmrane. ?fiis IS classified as the 4s +-/t (ES,+ Al) transition. The molar absorptivity (em) for the absorptxon spectrum f~ m P mole-’ cm-l.
Volume
77, number
1
CHEMICAL
PHYSICS LETTERS
?I
4 *
V
-06 12
or
06
-06
19
192.2
4
WAVEtLENGR-i
’
I
19:
1741
WAVELENGTH
Frg. 2. Examples of the absorption (.4o), unpoiarrzed bght ele~t~o~~ornlsm (--f#‘nl!o) and 90” polarued light eiectrochromtsm (-ff90fp)kpectra for the 1922A band of thurane This IS ciasstfied as the 4p - I) (A 3-A 1) transthon The molar ahsorpttvrty (em) for the nbsorphon spectrum IS m Q mole-* cm-’
Trtble 1 E?rpenmental
1
174.7
kern)
I735
(nm)
Fig 3 Examples of the absorption @to}, unpolarraed hght electrochromrsm (--en/& and 90° pohurrzed hght electrochronusm (-1F’/P) spectra for the 1740.4 band of thurane. Thrs IS classuied as the 3d - II (B I+- At) transthon. The molar absorpttvtty (em) for the absorptton spectrum LSm P mole-’ cm -r
coefticrenrs
Cle’Q dunethyl
sulfide 2284 d
NPEa) UPE b)
dunethyl
sulfide
1959 A
@p
(em-a)
(-2 8 t 0.7) x 104 (-27zO4)%104
(1.9 t 0 91 x to-2 (9 1 +-8 0) x 10-s
NPEa) UPE b)
(-3 5 +_1.6) x ,103 (-7 6 i 1.7) x IO+
(-2 6 iz 1.0) x ltYz (5.3 = 2.0) x t0-z
-59207 -14St 17
f-9.6 (-6.3
+ 3 9) X IO4 + 1.8) x IO4
(2.4 c 0.7) x 10-i (L.7 t 0 6) x LO-’
-15 6 -14 0 -8 8 ?I 2.4
(-8.8 I-i.0
f 5.3) x iO-+ f 0 9) X 104
(5 0 +4 5) x Lo-2 (1 2 f 0 9) x 10-t
-8.6 -I$.2
t l.S t 2.5
(-2.4 (-1.5
f 0 5) x 104 e 0.7) x 10-4
(I 3 rO 9) x IO-’ (8 9 t 4.2) x 10-2
-55.3 -44.5
t 4 5 t 3.1
thtkine
2122 A
NPE a) UPC b)
ihtirane
1922 Jk
NPE a) UPE b)
thhmne
17401%
NPE a) wEbI
e) PO” pohwized
C$‘p(cm-t)
right eIectrochromtsm.
b) Unpokinzed
-12.7 -94
f. 0 6 x06
hght eiectrochromrsm.
219
CI-ILXIICAL Ptik SICS LETTERS
Volume 77, number 1
1 January
1981
Table 3
Calculrtted ewlted-state parameters far DAIS and thtlrane a*b) --_-.- ~---^ _--- --- --1____-----RUlldh~ISUlfX~ Paranwter ~-_
--.--_
2xu
-
Q Eiex 0 R(‘)
_.
x
_ .“... _-
-
76201 -12ZOl (S3 I 27) 6 3~ 1O-5
b %.?\ ~EI)o =
-_
--
I-~----
- .uc, LSthe
-160 156
550 ZLO - -
-_-
----
--.
1959X _ -- _--17=07-I 7502 (16 ~23) 15UlO”L -3.50 3-13 _---
-
- --
5 150 = 150 ---___-
~__”
-_--
Tlwrnnc --..
-___-__
2iXh - --
--I---27105 -1120.5 (90) 22x10”
f-150) I30 .-
._-- -_
-
--~
--
1922 A -~--_~ 29r03 -1.3 5 0 3 t 19) (1s 1OYlO”4
1740x
(-400) 400 _-.-
-1560 I555
-
_---------
56kO3 -31=03 (83 c 17) 43x104 I 360 + 360
cfipolr moment change CD), JIM, IS the ewrted-state
cbpole moment (D), U IS the angle between t~.tnsruon manwxn and dipole moment ckmge (de@, A’(’ f IS n perturbntron term (au cm/erg). b = ag - eye\ IS the mean pol~~~b~t~ change (-x3) ,~,a\ IS the exited-state poI.uizabtitty f q3) b) Uncerrrwntrcs when determmed mrbcate the stand.ud error of the rwzm at the 9.55 confidence level ‘19
polarlrabilw, changes from the ground- to the etctcedstate ,md certdm ~erturb~tIo~1 terms The determmatwn of t1te.w quantrttes from the coeftic~ents C, and C2 resulted m large uncertamtles due to the large reinwe uncert3mttes ot these coettkients The coeffictent C;, however, IS purely a functton of the dipole moment change between the two stntes Hence, rhls property IS deternuned wth hlgher rellabrllty Thus 1s reflected in the low reiative unocrt~tnry as compared with rhe other properws The dverage v&~es determtned for the coefficients and therr respective standard errors of the mean at the 95% confidence level ate given In table 3 The wlues were determined from a n~[r~inIu~n of ten runs Error bars are mdlcated on exft spectrum The polartzstton of the transitions are given as 0 m table 3 The change m tfte dipole moment and the mean pofanrabti!ty change between the sates are lrsted as LIand b, respecwely The determmat1on of both the rnasn,tude .md sign of these propertres from the coefficlents has been deswbed [I ] These quantities are deftned by the rekrons a = ,ug- ,ue,and b = CQ-txe, where the subscrlpt g refers to the ground stateDand the subscnpt ex refers to the excited state The evclted state IS expected to have a larger mean pola~zab~tty than the ground state. thus the value for a;, LSexpected to be larger than a resulting HI a negattve value for b. The mngmtude an d s!gn associated with b were used to ciliculare the sign of LI Provided the ground-state propertles are avaIlable, the exIted-state values can be determmed from a andb. 220
The excttcd-state quantltles and the values for a and b are given m table 3 for each of the bands investigated From these absorptton data for DRfS and thglrane, the ewted-state dipole moment was found to be less tflan that of the ground-state The sign of P_ was determmed to be negattve This IS interpreted as electron density being sl-ufted onto ihe carbon end of the molecules m these e\cned-states In awilly symmetric moiecules of CT+ point group .md higher, the polartzatlon of the transtt$on must be either parallef or perpendicular wth respect to the mdJor aus of symmetry The mtenslties of the signals (-Z,/Io) for the poiartzed and unpolartzed spectra are known to be dtfferent dceordrng to the polarization of the transition, therefore, the polarlzatlons can be determined quahtatlvely even though the agnals are too weak to permit quaintltarive fitting of the data to the throrettcal espresston This IS accornphshed by comparmg the mtenstttes of the slgnal mamma between the two types of spectra. The angle of the polanzatlon 1s gwen m table 2 m the row labeled 8. The polarlzation of the transItIon determined can be used to rud the assignment _ The ground state for both DMS and thnrane has
been cafculated to have the highest occupied orbital of b, symmetry tocahzed tn the lone-pair 3p orbItal on the sulfur [5,6,9--12). The 4s -II Rydberg transltlons (2284 ,& m DMS and 2122 W m thurane) are classified by symmetry as BI C- A1 transitIons polarrzed perpendrcular to the major a;yIs. The polarizatton angles determmed for these absorptlons support the assignments.
Volume 77, number
1
CHEhItCAL PHYSICS LETTERS
Several posslbdlttes elclst for the 4p - 12 (19598 in DMS and the 1922 a m thurane) and the 3d +H (1740.4 rn thmane) Rydberg transxtxons. The p and d Rydbergs could be either a transrtron to a B, or A, state. The poiartzntton an&e for these absorprlons supported the A1 + At asstgnment for the p and the Bt * A1 asstgnment for the d Rydbergs The parameters, the change m the dipole moment and the change m the mean poIarlzabtl~t~es, can be used to characterrze the absorptrons The values of the e\crted-state properties determmed Imply characterlstlc differences among the translt~ons with respect to the magnrtudes for the parameters These parameters suggest factors that are ~portant in considenng the bonding dtfferences m the molecules The change m the dipole moment assocrated wtth these compounds ~3s found to be smlilar m magmtude and dtrectton as abserved for the s Rydberg transtttons m the ketone compounds [I ,2] _ The change m dtpoIe moments observed for DMS and for thrrrane IS from 2 6 to 2 9 D for the s and p Rydberg transrttons resultmg m the lie, bemg less than and m the oppostte dtrectron to ti, The drpole moment change for the d Rydberg trnrwtlon m thnrane nas the same sign but IS almost twce as large as the v.tlue for the s and p Rydbergs (5.59 D) This difference IS attnbuted to the penetratlon of the core orbitals by the ewted-state orbital slmllarly to that observed for atomic transrtlons [6]. The s and p Rydberg orbrtaIs have precursors m the core
and are
expected to rn~x stgmficantly
whereas
the d orbttal lacks precursors and IS less penetrating Thus penetration of the Rydberg orbrtals IS evidenced m the change m polarrzabdtty. The change m polartzabrhty for the two compounds IS found to increase from the s to p to d Rydberg transrttons Prevtous results for the cychc ketones e_xhrbrted larger polartzabrhty changes than the alkyl ketones [1,2] _ The results obtained for these sulfide conlpounds are conststent wtth the ketone data but do not show a srmtlar rmg effect. The relative change ur polarrzablltty IS consrstent for these conlpou~ds. For DMS, tms change varies for the s p Rydbergs to be about 1 2.2 while for thnrane, the s p d Rydbergs is found to be about 1.2.7 10. These results do not rule out other posstble assignments except those forbtdden by symmetry constder-
1 Janua.ry
19si
atrons. The magnitude of both the change ~1 dipole moment and m the mean polarizabillty support the extravalerit assrgnments smce populatton of a large moiecula, Rydberg orbttal would be expected to have large magnitudes associated wrth these propertaes Further mvestrgatrons of the sulfides usmg electrrcfield techniques to determme the extent the nng mfluences these parameters are m progress The authors gratefully acknowledge the financral support of thrs research by the Robert A Welch Foundation and the North Texas State UIllversIt~~ Faculty Research Fund
References
Ii1 G C Causley and B R Russeli, J Citem Phys 72 (1980) 1673
r21 G C_ Causle:8 and B R Russell, J 4m Chem Sac, 101 (1979) 5573
I31 J D Scott and B R Russeti 3 Cbem Phys 63 (1975) 3143 VoI I,ed EC Lim I41 W Lrptsy, m Ewtedstates, (Acsdemrc Press, New Yorh, 1974) p 129, and reFerences therein [Sl L B Clark and WT Simpson J Chem Phys. 43 (1965) 3666 [cl hl B Robm, L-l~ghet ewltcd states of polyatomic molecules, Vols I ,2 (Acndemtc Press, New York, 1974) p 176 N Brtsco and R D Morse, Chem Phys Letrers 20 (1973) 404 S 5 Thompson, D-G Carroll, F Watson, Xl. O’Donnell and S P hl&iyM, J. Chem Phys 45 (1966) 1367 E J. hIcA!duffand K-N Houk, Can J Chem 55 (1977) 318 G L Bendazzolt, C GottareUl =d P Palmterx,J Am Chem. Sot. 96 (1974) 11 S Cradock and R A Whrteford, 3 Chem. Sot. Ckradap TKlns II 68 (1972) 281. D-C. Frost, F G Herrmg, A Katnb and CA hIcDowetl, Chem Phys Letters 20 (1973) 401. J.D Scott, G C Causiey and B.R. Russell, J. Chem. Phys 59 (1973) 6577 E R Lipp~ncott,G i%SgZtKtJm and J hl Stutman, J. Phys Chem 70 (1966) 78 L Pterce and hf Hnyashi, J Chem Pb>s. 3S (1961) 4’79. A N Vere~cha~, A P Anastas’eva and S G. Vul‘fson, IN Akad Nauk SSSR Ser. Rhim. (1969) 551.
G.L Cunrungham, A W. Boyd, R.J. hfyers, W.D. GWM and W I. LeVan, J. Chem Phys 19 (19.51) 676.
221
Volume 77. number 1
ELECTRIC
DICHROISM
1 Jarmar>
1981
SPECTROSCOPY IN THE VACUUM ULTRAVIOLET
DIMETHYLSULFIDE
AND THIIRAN
Dame1 D ALTENLOH
and B R. RUSSELL
Deparitnerit ojCI~er?~~srr)~ Xorth Teras Srare Utrtt erstry, Detrro~~, Teros 76-703 L/SA Kecened 6 August 1980. III final form 8 October 1980
Eleculc field techmques have been used to mvesugate certam s, p and d Rydberg absorpuon bands for dunethylsulfide (DXIS) and ethylene sulfide (thurnne) wth respect to the polarlzatIon of the translhons, the &pole moment, nod mean polar-
~znbht~ changes that occur upon
cxcnatlon
A techruque using Intense electric Gelds, electnc lmear &chroism (ELD) ha been developed and dcscribed m previous amcles and used to obtain certam ekcned-state propertles [14] These parameters are the change m dipole moment between the ground and evclted states, the corresponding changes m polarizablhcy. and the angle between the electnc dipole transltlon rnornent and the change m &pole moment between the two states (polarlzatlon of the transition). These parameters are used to help charactenze electronic states for certam absorptlons for dunethylsulfide (DMS) and thhrane (ethylene sulfide) The absorptlons Investigated are the 2122 A band of thurane and the 2284 a band of DMS, the 1922a band of thurane and the 19598 band of DMS, and the 1740A band of thurane previously rdentlfied as the 4s -II, 4p +-II, 3d + iz Rydberg cransltlons, respectively [5,6] (table
I)nese two dlvalent sulfur compounds are the slmplest of two classes, the symmetnc straight-cham atkyl sulfides and the cychc sulfides. The basic difference between these two classes of compounds IS the bresence of the ring. Assuming that the geometries reman unchanged upon excltatlon for these compounds, then excited-state properties with respect to the structural restnctlons of the ring can be inferred from the results of the electnc-field data. The vacuum ultravioIet
at dlstmgulslung the Rydberg from the non-Rydberg for senes of sulfur compounds. They noted that the energes of Rydberg absorption bands appeared to “line up” when the ionization potenmls were ahgned. Robln [6] presented extensive arguments based on term values and sunddntles with the oxygen analogs to assign the absorptlons to be discussed. These pre-
rlbsorptlons
vlous assignnlents
were in apparent
contrackclon
to
those of Basco and Morse [7]. The results obtained from the electric-field studies are consistent with the assignments of Clark and Simpson and Robin Vapor-phase spectra for timethylsulfide and thurane were obtamed with apparatus wiuch has been described prevrously [ 1 _I] _Certam modlficatlons have been made to Interface wrth a microprocessor (Apple II+). The ELD signal was obtamed by locking-m on the fundamental of the ac fields. Thus slgnal IS four times as Intense as the overtone used prewously Examples of the ELD and absorption spectra for the s, p and d Rydberg bands for thurane are gven in figs. 1-3. Slmllar spectra for the s and p Rydberg bands for DMS were obtamed but are not shown Analysts of these spectral data IS accomphshed by a least-squares fit to the theoretical expression below [ i,3]. The theoretlcal denvation of tlus equation as well as the manner the data 1s treated to obtam certam excited-state parameters has been described [ 11.
217
TiIble 1 ~ornp~a~on of data for ~rne~~~ut~de znd thmanc a) ~_ ~_I______ ____-__ ---__ --lon=rltion
-
-__
______Dimethyl sulfide
-
term value (cm-‘)
72891
4sAk 4PBI 3dAI
43870 5116.5 56290
47 125
s
26500
26000 21000 SO00
II
52029 5749 1
19100 13800
IlP rid
1 5Oc-0.01
ground-srate &pole moment (D) me.m polxrlzsbdtty ( k3)
c-s
4 73
1 802
1 819 1492
98” 52’
65” 48
C-C
bond an&e
c-s-c
1.5x lo-’
4SA, ~PBI 3dA1
1.65+0 01
33
7
bond length (Sr)
-Thurime
70092
potentul (cm-’ )
transxtronenergy (cm-‘)
ground-state
J.Januxy 1981
CHEMICAL PHYSICS LETTERS
Volume 77, number 1
2 2x 10-3
4 8x 1O-3 1.9x 10-z 1.2x10-
n) Data obtaned from refs [6 13-17)
6-O
45
(1)
30
VO % ;;
I.5
where Go, Z,I 1s the energy regon for the absorption band (cm- 1); A"(Z),dAo(~)~d~ and d2A0(3)fdZ2 are the absorption profile and the correspondmg first and second derivatives, -f,/f O(E) IS the electrtc field
S 00 25
SIgnal.
The results of the least-squares fit are given m table 2 for the coefficw&s C, , CT,, and C, for the absorptions studed. The coeffictents C, and C2 represent terms mvokng ground- and excited-state quantities. These quantities include the &pole moment and mean 4
WAVELENGTH
(nm 1
Fig 1. Examples of the absorption (r1O), unpolarized h&t elecuochrom~m (-fpn/io) and 90” polarized hght electrochiomism (-Iz”/lo) spectra for the 2122 II band of tbmrane. ?fiis IS classified as the 4s +-/t (ES,+ Al) transition. The molar absorptivity (em) for the absorptxon spectrum f~ m P mole-’ cm-l.
Volume
77, number
1
CHEMICAL
PHYSICS LETTERS
?I
4 *
V
-06 12
or
06
-06
19
192.2
4
WAVEtLENGR-i
’
I
19:
1741
WAVELENGTH
Frg. 2. Examples of the absorption (.4o), unpoiarrzed bght ele~t~o~~ornlsm (--f#‘nl!o) and 90” polarued light eiectrochromtsm (-ff90fp)kpectra for the 1922A band of thurane This IS ciasstfied as the 4p - I) (A 3-A 1) transthon The molar ahsorpttvrty (em) for the nbsorphon spectrum IS m Q mole-* cm-’
Trtble 1 E?rpenmental
1
174.7
kern)
I735
(nm)
Fig 3 Examples of the absorption @to}, unpolarraed hght electrochromrsm (--en/& and 90° pohurrzed hght electrochronusm (-1F’/P) spectra for the 1740.4 band of thurane. Thrs IS classuied as the 3d - II (B I+- At) transthon. The molar absorpttvtty (em) for the absorptton spectrum LSm P mole-’ cm -r
coefticrenrs
Cle’Q dunethyl
sulfide 2284 d
NPEa) UPE b)
dunethyl
sulfide
1959 A
@p
(em-a)
(-2 8 t 0.7) x 104 (-27zO4)%104
(1.9 t 0 91 x to-2 (9 1 +-8 0) x 10-s
NPEa) UPE b)
(-3 5 +_1.6) x ,103 (-7 6 i 1.7) x IO+
(-2 6 iz 1.0) x ltYz (5.3 = 2.0) x t0-z
-59207 -14St 17
f-9.6 (-6.3
+ 3 9) X IO4 + 1.8) x IO4
(2.4 c 0.7) x 10-i (L.7 t 0 6) x LO-’
-15 6 -14 0 -8 8 ?I 2.4
(-8.8 I-i.0
f 5.3) x iO-+ f 0 9) X 104
(5 0 +4 5) x Lo-2 (1 2 f 0 9) x 10-t
-8.6 -I$.2
t l.S t 2.5
(-2.4 (-1.5
f 0 5) x 104 e 0.7) x 10-4
(I 3 rO 9) x IO-’ (8 9 t 4.2) x 10-2
-55.3 -44.5
t 4 5 t 3.1
thtkine
2122 A
NPE a) UPC b)
ihtirane
1922 Jk
NPE a) UPE b)
thhmne
17401%
NPE a) wEbI
e) PO” pohwized
C$‘p(cm-t)
right eIectrochromtsm.
b) Unpokinzed
-12.7 -94
f. 0 6 x06
hght eiectrochromrsm.
219
CI-ILXIICAL Ptik SICS LETTERS
Volume 77, number 1
1 January
1981
Table 3
Calculrtted ewlted-state parameters far DAIS and thtlrane a*b) --_-.- ~---^ _--- --- --1____-----RUlldh~ISUlfX~ Paranwter ~-_
--.--_
2xu
-
Q Eiex 0 R(‘)
_.
x
_ .“... _-
-
76201 -12ZOl (S3 I 27) 6 3~ 1O-5
b %.?\ ~EI)o =
-_
--
I-~----
- .uc, LSthe
-160 156
550 ZLO - -
-_-
----
--.
1959X _ -- _--17=07-I 7502 (16 ~23) 15UlO”L -3.50 3-13 _---
-
- --
5 150 = 150 ---___-
~__”
-_--
Tlwrnnc --..
-___-__
2iXh - --
--I---27105 -1120.5 (90) 22x10”
f-150) I30 .-
._-- -_
-
--~
--
1922 A -~--_~ 29r03 -1.3 5 0 3 t 19) (1s 1OYlO”4
1740x
(-400) 400 _-.-
-1560 I555
-
_---------
56kO3 -31=03 (83 c 17) 43x104 I 360 + 360
cfipolr moment change CD), JIM, IS the ewrted-state
cbpole moment (D), U IS the angle between t~.tnsruon manwxn and dipole moment ckmge (de@, A’(’ f IS n perturbntron term (au cm/erg). b = ag - eye\ IS the mean pol~~~b~t~ change (-x3) ,~,a\ IS the exited-state poI.uizabtitty f q3) b) Uncerrrwntrcs when determmed mrbcate the stand.ud error of the rwzm at the 9.55 confidence level ‘19
polarlrabilw, changes from the ground- to the etctcedstate ,md certdm ~erturb~tIo~1 terms The determmatwn of t1te.w quantrttes from the coeftic~ents C, and C2 resulted m large uncertamtles due to the large reinwe uncert3mttes ot these coettkients The coeffictent C;, however, IS purely a functton of the dipole moment change between the two stntes Hence, rhls property IS deternuned wth hlgher rellabrllty Thus 1s reflected in the low reiative unocrt~tnry as compared with rhe other properws The dverage v&~es determtned for the coefficients and therr respective standard errors of the mean at the 95% confidence level ate given In table 3 The wlues were determined from a n~[r~inIu~n of ten runs Error bars are mdlcated on exft spectrum The polartzstton of the transitions are given as 0 m table 3 The change m tfte dipole moment and the mean pofanrabti!ty change between the sates are lrsted as LIand b, respecwely The determmat1on of both the rnasn,tude .md sign of these propertres from the coefficlents has been deswbed [I ] These quantities are deftned by the rekrons a = ,ug- ,ue,and b = CQ-txe, where the subscrlpt g refers to the ground stateDand the subscnpt ex refers to the excited state The evclted state IS expected to have a larger mean pola~zab~tty than the ground state. thus the value for a;, LSexpected to be larger than a resulting HI a negattve value for b. The mngmtude an d s!gn associated with b were used to ciliculare the sign of LI Provided the ground-state propertles are avaIlable, the exIted-state values can be determmed from a andb. 220
The excttcd-state quantltles and the values for a and b are given m table 3 for each of the bands investigated From these absorptton data for DRfS and thglrane, the ewted-state dipole moment was found to be less tflan that of the ground-state The sign of P_ was determmed to be negattve This IS interpreted as electron density being sl-ufted onto ihe carbon end of the molecules m these e\cned-states In awilly symmetric moiecules of CT+ point group .md higher, the polartzatlon of the transtt$on must be either parallef or perpendicular wth respect to the mdJor aus of symmetry The mtenslties of the signals (-Z,/Io) for the poiartzed and unpolartzed spectra are known to be dtfferent dceordrng to the polarization of the transition, therefore, the polarlzatlons can be determined quahtatlvely even though the agnals are too weak to permit quaintltarive fitting of the data to the throrettcal espresston This IS accornphshed by comparmg the mtenstttes of the slgnal mamma between the two types of spectra. The angle of the polanzatlon 1s gwen m table 2 m the row labeled 8. The polarlzation of the transItIon determined can be used to rud the assignment _ The ground state for both DMS and thnrane has
been cafculated to have the highest occupied orbital of b, symmetry tocahzed tn the lone-pair 3p orbItal on the sulfur [5,6,9--12). The 4s -II Rydberg transltlons (2284 ,& m DMS and 2122 W m thurane) are classified by symmetry as BI C- A1 transitIons polarrzed perpendrcular to the major a;yIs. The polarizatton angles determmed for these absorptlons support the assignments.
Volume 77, number
1
CHEhItCAL PHYSICS LETTERS
Several posslbdlttes elclst for the 4p - 12 (19598 in DMS and the 1922 a m thurane) and the 3d +H (1740.4 rn thmane) Rydberg transxtxons. The p and d Rydbergs could be either a transrtron to a B, or A, state. The poiartzntton an&e for these absorprlons supported the A1 + At asstgnment for the p and the Bt * A1 asstgnment for the d Rydbergs The parameters, the change m the dipole moment and the change m the mean poIarlzabtl~t~es, can be used to characterrze the absorptrons The values of the e\crted-state properties determmed Imply characterlstlc differences among the translt~ons with respect to the magnrtudes for the parameters These parameters suggest factors that are ~portant in considenng the bonding dtfferences m the molecules The change m the dipole moment assocrated wtth these compounds ~3s found to be smlilar m magmtude and dtrectton as abserved for the s Rydberg transtttons m the ketone compounds [I ,2] _ The change m dtpoIe moments observed for DMS and for thrrrane IS from 2 6 to 2 9 D for the s and p Rydberg transrttons resultmg m the lie, bemg less than and m the oppostte dtrectron to ti, The drpole moment change for the d Rydberg trnrwtlon m thnrane nas the same sign but IS almost twce as large as the v.tlue for the s and p Rydbergs (5.59 D) This difference IS attnbuted to the penetratlon of the core orbitals by the ewted-state orbital slmllarly to that observed for atomic transrtlons [6]. The s and p Rydberg orbrtaIs have precursors m the core
and are
expected to rn~x stgmficantly
whereas
the d orbttal lacks precursors and IS less penetrating Thus penetration of the Rydberg orbrtals IS evidenced m the change m polarrzabdtty. The change m polartzabrhty for the two compounds IS found to increase from the s to p to d Rydberg transrttons Prevtous results for the cychc ketones e_xhrbrted larger polartzabrhty changes than the alkyl ketones [1,2] _ The results obtained for these sulfide conlpounds are conststent wtth the ketone data but do not show a srmtlar rmg effect. The relative change ur polarrzablltty IS consrstent for these conlpou~ds. For DMS, tms change varies for the s p Rydbergs to be about 1 2.2 while for thnrane, the s p d Rydbergs is found to be about 1.2.7 10. These results do not rule out other posstble assignments except those forbtdden by symmetry constder-
1 Janua.ry
19si
atrons. The magnitude of both the change ~1 dipole moment and m the mean polarizabillty support the extravalerit assrgnments smce populatton of a large moiecula, Rydberg orbttal would be expected to have large magnitudes associated wrth these propertaes Further mvestrgatrons of the sulfides usmg electrrcfield techniques to determme the extent the nng mfluences these parameters are m progress The authors gratefully acknowledge the financral support of thrs research by the Robert A Welch Foundation and the North Texas State UIllversIt~~ Faculty Research Fund
References
Ii1 G C Causley and B R Russeli, J Citem Phys 72 (1980) 1673
r21 G C_ Causle:8 and B R Russell, J 4m Chem Sac, 101 (1979) 5573
I31 J D Scott and B R Russeti 3 Cbem Phys 63 (1975) 3143 VoI I,ed EC Lim I41 W Lrptsy, m Ewtedstates, (Acsdemrc Press, New Yorh, 1974) p 129, and reFerences therein [Sl L B Clark and WT Simpson J Chem Phys. 43 (1965) 3666 [cl hl B Robm, L-l~ghet ewltcd states of polyatomic molecules, Vols I ,2 (Acndemtc Press, New York, 1974) p 176 N Brtsco and R D Morse, Chem Phys Letrers 20 (1973) 404 S 5 Thompson, D-G Carroll, F Watson, Xl. O’Donnell and S P hl&iyM, J. Chem Phys 45 (1966) 1367 E J. hIcA!duffand K-N Houk, Can J Chem 55 (1977) 318 G L Bendazzolt, C GottareUl =d P Palmterx,J Am Chem. Sot. 96 (1974) 11 S Cradock and R A Whrteford, 3 Chem. Sot. Ckradap TKlns II 68 (1972) 281. D-C. Frost, F G Herrmg, A Katnb and CA hIcDowetl, Chem Phys Letters 20 (1973) 401. J.D Scott, G C Causiey and B.R. Russell, J. Chem. Phys 59 (1973) 6577 E R Lipp~ncott,G i%SgZtKtJm and J hl Stutman, J. Phys Chem 70 (1966) 78 L Pterce and hf Hnyashi, J Chem Pb>s. 3S (1961) 4’79. A N Vere~cha~, A P Anastas’eva and S G. Vul‘fson, IN Akad Nauk SSSR Ser. Rhim. (1969) 551.
G.L Cunrungham, A W. Boyd, R.J. hfyers, W.D. GWM and W I. LeVan, J. Chem Phys 19 (19.51) 676.
221