- Email: [email protected]
Rydberg transitions in the ultraviolet spectra of difluorobenzenes
RYDBERG TRANSITIONS
IN THE ULTRAVIOLET
SPECTRA OF DlFLUOROBENZENES
R. GILBERT0 and C. SANDORFY D&arremenr de Chimie. Universire’de Montr6al. Monrrehl. Qukbec, Canada Received 27 May 1974
Two Rydberg series are found in the electronic absorption spectra of the three difluorobenzenes which conveige to the lowest ionization potential. Superimposed to the first ionization continuum bands belonging to a Rydberg series related to a higher IP are found. The problem of its assignment is discussed.
1. Introduction It has been known since the works of Price and Wood [I], Wilkinson [2] and El-Sayed et al. [3] that Rydberg series are found in the spectrum of benzene both below and above the first ionization potential_ At frequencies lower than the first IP we find - in addition to the three well known x* + ir bands - Rydberg series of two types; (a) a series of the np type with a quantum defect of the order of 0.50, and (b) series having a low quatitum defect of about 0.05. The latter might be of the nd type in which case they are g ++ g
and forbidden by the Laporte rule or nf in which case they violate the approximate atomic selection rule, AL = 0, f l_ Both types of series converge to the lowest
trifluorobenzene
[14], penta- [12] and hexafluoro-
benzene [ 12, 131 have also been studied. The most interesting point is perhaps the following: whereas the
photoelectron spectra give clear evidence of the sp!itting of the elg orbital in derivatives having no threefold axis, the vacuum W spectra do not seem to be affected by this. The expected splitting of the allowed LElu + I Alg ?* + n band has never been clearly_observed. Furthermore, although under these lower sym-, metries ns and nd type series become allowed and there could be a greater number the series which were ungerade in benzene none of these have been shown to
c. . .. ’
exist. Only two Rydberg series (related to the lowest
II ionization potential (9.25 ev) which is related to the elg orbital [4]. The relative insensitivity of n electron energies to
IP) were found in all the fluorobenzenes examined so far and these are of the types described above: one with a high quantum defect (?I$) and one with a low quantum defect. (However, Smith and Raymonda [ 121 go not mention the np series for hexaflu&obenz@neJ
fluorine substitution ES-8 ] and the non-interference ofthe fluorine-A03 in the related part of the spectrum
The three lowest II% of fluorobkene (FB) are at 9.20 (ad), 9.56 (vert) and 11.7 (ad) eV [4]. Nthough
makes the study of the spectra of fluorobenzenes interesting:In a previous publication [9] from this labora-
in benzenejtself there might be a o level between the elg and aIu n leveis th&e is little doubt that in fluoro-
tory the bands due to valence-shell transitions in the vacuum ultraviolet spectra of aseries tif fluorobenzenes have been discussed. The Rydberg bands of monofluo.robenz&e (FB) have been studied by Hammond et al..
benzen&, wjth the:possible exceptiqn of FB, alI’n levelk are at e+rgies lower than the lowest u level. So .th$ _ -second IP of FB. resuI& from-th& splitting :o.fthe e’,, or-._.
’;
‘.-
Volume 27, number 4
CHEMICAL PHYSICS LETTERS
reassigned these bands to the n = 3 member of a series converging to the third IP with a quantum defect of 0.55. One o.f the alms of our work on the ditluorobenzenes has been to ascertain if similar bands exist in the spectra of the latter.
2. Interpretation
of the spectra
The photoelectron spectra of the three difluorobenzenes, henceforth designated as (1,4), (1,2) and (1,3) have been-measured prevIousIy by Baker et al. [15] , by Murrell and Narayan [ 161 and by KIessinger [17] _Our values differ only very slightly from theirs. Of interest to us are the three lowest IP’s of each compound which are: (1,4) : 9.18 (ad), 10.07 (advert), 12.12 (ad); (1,2) : 9.30 (ad), 9.93 (vert), 12.63 (vert); (1, 3) : 9.35 (ad), 9.94 (vert), 12.22 (ad). (ad = adiabatic, vert = vertical, advert = vertical and adiabatic.) The split in the elg IF of benzene is quite significant: O-67,0.43 and 0.42 eV in the above order. Figs. 1,2 and 3 show the absorption spectra and the numerical data are compiled in tables l-3. It is quite clear that aII three molecules possess the two usual Rydberg series converging to the lowest IP: one with a quantum defect of about 0.5 and another with about 0.05. In eachcase the vibrational fine structure of these
15 August 1974
bands is very similar to that found in the respective photoelectron spectra. The vibrational intervals are found, about 400-500,850--1000, and 1250-1450 cm-l. They are similar to those found for (I, 3,5) [14] and we shall not discuss them in detail. The lowest IP of (1,4) is at 74050 cm-l. At slightly lower frequencies, at 73700 cm-I we fmd a IocaIly prominent band. Since there is a similar band in the spectrum of (1,3,5) [14] we assign this band to the n = 3 member of a series converging to the third IP with a quantum defect of 0.86. [(I, 3,s) which has D3b symmetry has of course no “second” II’.] On the other side of the IP we found seven weaker bands, 74850,75600,76730, 77650,78200,78600 and 79030 cm-l_ This group of bands resembles those found in the same spectral range for FB. Following Smith and Raymonda [ 121 these bands should be interpreted as vibrational bands belonging to the transition with origin at 73700 cm-l. We made an attempt to interpret these bands as belonging to a series converging to the second IP. This is only possible, however, if we suppose that the lower members of the series are among the bands found in the dense 68000 cm-l region_ We have no real proof for this, however_ In (1,2) and (1,3) the situation is similar. The first IF is at 75020 and 75350 cm-l for (1,2) and (1,3), respectively. Close to these we find again one relatively intense band for both molecules (75200 and_ 75500 cm-l) which are readily assigned to the n = 3 member of a series converging to the third P. Going to higher
CHEMICAL PHYSICS LElTERS
Volume 21, number 4
llnmf 150
160
-_
74
FREQUENCY
1974
130
I40
70
66
62
1.5 Aue;ust
78
(cti’) x tCi3
Fig. 2. The Rydberg bands of 1,2-difluorobenzene.
X 0-m) 150
160
130
140
1
I 62
FREQUENCY
78
74
70
66
(cf&c
Id3
Fig. 3. The Rydberg bands of l,f-d.iflnorobenzene.
frequencies.~e spectrum of (I, 2) becomes diffuse but in that of (1,3) we fmd weaker bands at 75500,75800, 76500,76800,77100 and 77300 cm-l posing the same problem as in the case of (1,4). Now, it seems to be worth noting that the quantum defects are of the order of 0.85 for (I, 4), (I, 3, (I ; 3) ami (1,3,5) and Smith and Raymonda found 1. I.5 for penta- and hexafhrorobenzene. In all these cases the: series is tif the ns type, related to the aZu_IPof hen; Zen+. On the other hand Smith and Raymonda fourid-.’ _ &-I “p 6~ skies with a quantum defect &f 0.55 for
FI3. According to Koch and Otto [lSj , Jonsson and Lindholm [lQ] and Robin [20] a sharp Iine at 73880 cm-r in the spectrum of benzene itself can be assigned to &he3p f 3e2, transition, an dowed transition related to the lowest o iP. One possible explanation of the great difference between the quartturn defect of : : ti Q$er Rydberg series for FB and the more%eayy fluorini subst&itod detivatives of benzene that comes ... in mind.is t&it for FB the band is stiil related to a. ‘. IRydbGg se&j conv&gkg t.@the’lotiest ” I~Ai& [email protected], benzene i&If but.‘that in the dthorsjtis #at@ to that:
I’ . ._ .. : : 1._ps9.-. ;: _ .: ) .,, . ... -~.. . 1.. _:_ .. : . .‘.. ._. :,__ -.’ :.” .‘. .‘. ,.: : .: ‘.:.. . - ,.. _,’ .,’ : -:;_..‘:‘_~ :.. ‘_ _.,_ ,_ ;_.I ._;:: ,: -: -.-I f’-,,-.. .._._,.__‘“.‘_. _‘.” .:__-_;_ ._(. -:- ._‘. -- “_ : 1,;‘. - “.- -,. . . _. I... .: -,--.:.. ,-. ,I,:, .,. :.,. ._.;.: .:- :. .-y ,~. .. ,--. ‘,,:‘-,y:.r.;~.: :.:,:‘.,, “,e_., .’ :.,.T :_ ,‘-:::. ,,;.’ ;:-: .,.;-I, 2...,::.___: ; .,, ,, -1’ “‘.,-..__:‘,-. 1‘. :.y.:... ..,. _.,, ., _ ._..:.. .I 1:: ,:,..Z’ ; :.:“I ,-.; ?:;_‘;p. ._. ;::..,:_:.,L_‘.:.;i:__;,, ,,,:.,;;, _..~;:~‘:_,‘_,z~“ <,T’..:.; ._;._ ~:‘ :.;._-.-r._ __-_r_-,.~.. ,_;, .....__Y,, :,,~~-_.-.‘;: ,;_::.‘.,.:.,r.‘: ,_._‘.:‘,” ‘.:l.;.,;.~,I_,“--._ ; _.: .7.’ .:..“-’ :. .:, j ‘-ril” ‘._: ‘.I: ;;;r.k,T.:., ::i~,.~:~~._~.,5%,i~... ~:~~,;i.(.,.,:~:~,-..~~~~~~.~-~~~-~.~”~’:~~~ i., .:..‘..‘,.,>,-*. ;..‘.:; ,z_; :-. ‘._‘.’.-.‘2. .: ; .;:2.:_:: - : +.-)L.y,;,: ,.;;I;: ..:, .._ _.... .(-&<<’ L. i.~:.,l~:‘:~.~.--r.,__-“. ,._.‘. :: :-;;.,.m<,r.-. ,:.. . . . . :-.i’_. :’i .;-.:.:_..y <,.. _. -,1. ... ._ .-.,v %I’_ _5. .=__i-‘m.:: ,,_+._-;:,*;..,;l-;-. .. ~_id_i. ” 1T_.,--..:.-:.. T--.’ ‘- ’ ,.=;‘ .;.::; 1i j,:-<.;.:;+p=: .,,.. i.;_,y‘ .rr_<
:
:
.. 1..:. . . .,
.__ :.
:
.
..
CHEMICAL PHYSICS LElTERS
Volume 27, number 4
\
15 August 1974
Table 1
Observed and calculated frequencies of Rydberg bands ccmverghg to the lowest ionization Potential of 1.4-difluorobenzene. Vibrational iutexvals associated with Rydberg bands
+(obs)
n
bti’
1
Vibration
~&alC)
(cm-‘)
(cm-’ )
unkaIc) - u,(obs) (cm-‘)
61120 66790
-100
69380
+10
70770 71610 72150 72520 72780
+40 -20 +90 i-20 -150
56060 64840
-30
68430
+10
70240 71280
0 +90
Series R; A = 0.07 3 4
66890 67320 67740 68120 69370 69810 70730 71630 72060 72500 72930
5 6 7 a 9 10
430 850
1230 440
Series RI A = 0.52 3 4
64870 65220 65660 66090 66450 68420 68860 70240 71190
5 6 7
350 790 1220. 360 430
has been a-&r) in benzene.
3. Conclusions
The results can be summed up as follows: (i) All three molecules possess one Rydberg series of the np type and one of the nf or nd type, both converg&g to. the lowest STIP. These series seem to be characteristk of all fluorobepenes and probably many other benzene derivatives. (ii) Wecould not obtain 3 decisive argument settling the pr6blem of th& +&gnment of the ba@s found in *UVspe&u&in the.v&ix&ofthef%tIP.Thus, id least for the tin&being, weare &dy to kept t&e -_: ~&i
-, ,;_
:.
.: ;
.. ; . : :
._.
)
more conservative assignment of Smith and Raymonda relating these to the third and not the second IP. It is possible, however, that for benzene and FB this is a o IP while for the more highly fluorine substituted derivatives it is the higher n IP. A number of questions remain unanswered and would warrani further research. (a) WhatZs the reason that no ns type Rydberg series converging to the first IIFare found even though these become allowed under the lower symmetry of many of the derivatives? (Acttii Ailen and Schnepp [21] .found an extra btid. in the circular dichroism spectrum of some berkjtie~eri~atives which ‘k+ns to have thti right location
to be.tl&3s
+-elk b&d.):
-.
: .,.
..
(b) The s&6 question can be asked ~oncerning’so~e :
_. .~:
._
-.,. :.
:
15 August 1974
CHENfCAL PHYSLCS LR’lTRRS
Vohrme 27, number 4
Table 2 Observed and cahxlated frequencies of Rydberg bands converging to the Lowest ionization potential of 1,2-dithiorobenzene. tional intervals associated with Rydberg bands Vibration fern-r 1
n
v&slc)
Vibra-,
- vnfobs)
mf-‘1
SeriesRi A = 0.03 3
62910
-1150
68390
-10
70910
-30
72250
72270
i-20
73080
73090
+10
64060 64540
480 1010
65070
1500
65560 65960 4
400
68400 68930
530 1000
69400 69790 70300
1390 510
70880
5
71410
530
71910 6 7
1030
Series Rr A = 0.46 58350
3 66600
4
67130
70020
-20
-20
1000 1380
67980 1010
68140 70040 70540
-10
530
67600
5
66590
500 1020
71060
1370
(71410)
6
71790
71770
7
72780
72780
8
73510
73420
9
73820
73S40
+20
10
74150
74140
-10
:. : .‘ effect on thi ultraviolet spktk? ‘ AH that F be Hd tit $T present stagk 2j ‘A< n&my of $e i&ted observatikisare manif&;itio~~ of tJxe2. I:, “ff . uorokffect” thai is the stiti effect df flUo~e4i3~~‘:
np .and nd manifolds. ’ (c) If the above argument iS correct .why are no ,, : Ry$erg s@fs observed which coqverge to.$he second IP r&ult@g from-the split of -tie elg orbital bf benzene? a&&&l
members
_
refie+h
.;’
_, .,
W
little
of the
: fa)Ho~tOexplainthattht:sizeabfe.spfitofthee~g:~ -J&l
~~~~hotoelectr0~
-. : -_’ .,_ ..‘ ._. -1‘
I-‘.
spe*.hj=
-
-,. __..“.’
0 -90
:StitUdb~,OXl6,-$1&~@1~~~$$~~
~O~~~.~~~e~~~
pidfo@d Sect:_.iin u-eItktron [SY$] ‘.,‘.’ “(; ’ ;;. ___ ei&rgies -.... : ..._._., .,,_, ~ _::._ ,,__:~~ __I _,._ ..::-_ ..,_.,L _. .( ...-. ;.._.‘, ., : :.,j ;_ .i; _.,,:. .. _‘,..” : .: .,-.; ‘ _,. ._’,: ..,.:; ,:. i _’ . .. .‘-, ,:,. _.’ : .‘ .,-__ ..,,
~,_: ::.
CHEMICAL
Volume 27, number 4
PHYSICS
LETTERS
15
August 1974
Table 3 Observed and calculated frequencies of Rydbcrg bands converging to the lowest ionization potential of 1,3difluorobenzene. tional intervals associated with Rydberg bands Vibr$ion (cm 1
n
Qzdc) (cm-’ )
QxIc) - +obs) (cm_’ )
62330 67960
-20
70530
+20
71910 72750 73280 73650
+30 - +60
Vibra-
Series R; A = 0.06 3 4
67980 68300 68530 69010 70510 7’1060 71630 71880 72690
5
6 7 8 9
320 550 (1030) 550 1120
73520
+130
Series RI A = 0.54 3 4 5
6 7 8 9. 10
65250 69480 70030 70790 71290 72450 73150 73520 73819
56900 65860 69510
+610 +30
71340 72390 73050 73490 73800
+50 -60 -100 -30 -10
550 1310
Acknowledgement
[5] C.R. Brundle, M.B. Robin and N.A. Kuebler, J. Am.eem. Sot 94 (1972)
References [i] W.C. Price and R.W. Woo& J:C lem. Phys. 3 (1935).439_. [Z] P-G. wilkinson; Can. J. Phys. 34 (1956) 596.. ~[3] .M.F:A. El-Sayed, M. Kasha and Y. Tanaka, J. Chem. Phys. :3+ (1961) 334. .: .: _:. ..: ._ .I [4j D-w. Tume&C.-Baker, A.D; Baker and C.R. BrundIe, .j :” &fi&di~ photoeI&ti&i~~ectios~py (Intersc&tiw, New ..,.- York.19701 chs:i0 and 11. &d references therein. .
1451.1466.
[6] I.D. Clark and D.C. Frost, J. Am. Chem. Sot. 89 (1967) 244. [7] D-W; Turner, Tetrahedron Letters (1967) 3419. .[8] G. Bilanger and C. Sandorfy, Chem. Phys. Letters 3 (1969) 6.61. [9] R Gilbert, P. Sauvageau and C. Sandorfy, Can- J. Cbem. 50 (1972) 543. [IO] V.J. Hammond, W-C. Price, J.P. Teegan and A-D. Walsh, Disc&ions Faraday Sot. 9 (1950) 53.. [ 1l] .R. Gib&t_and C. @ridorfy, &em. Phys. Letters 9 (1970 121. -[12] D:R..Smith and’J.W:.F&ymonda, Cherp;Phys. L&t&s 12
We acknowledge financial help from the National Research Council of Canada and a postgraduate scholarship to one of us (R.G.).
..
(1971)
269.
.[131.C. Slusc-Goffart and J_‘Mo&ny, .. .-. ‘_-:, ... (l?j&).2jl_-. :
.-
:
:
_-
.; _. _, _I _.
.:
(3h&:Ph$s.
Let&
25
Volume 27. number 4
CHEMICAL PHYSfCS LEkT.ERS
f 141 R, Gilberr, P. Sawageau and C. Ssndorfy, Chem. i%ys_ Letters 17 (1972) 465. [IS] A.D. Baker, D.P. hfay and D_W. Turner, J, Chem. Sot. B (196fs) 22. [16] B. Narayan and J.N. Munell, Mot. whys. 19 (1970) 169. [l? j M. Klessinger, Anger- Chem. 11 (1972) 525.
15 Axsgust1974
w-1 B.O. Jonssonand E. Lindholm, Ark& Fysik 39 (196% 65. M.B. Robin, Higherexcited states of po!y?tomic moleIX&S, Voi, 2 (Academic Press, New-York, 19741. S. Allen and 0. Schnepp, J. Cbem. Pbys., ta be publisbdd.
IN THE ULTRAVIOLET
SPECTRA OF DlFLUOROBENZENES
R. GILBERT0 and C. SANDORFY D&arremenr de Chimie. Universire’de Montr6al. Monrrehl. Qukbec, Canada Received 27 May 1974
Two Rydberg series are found in the electronic absorption spectra of the three difluorobenzenes which conveige to the lowest ionization potential. Superimposed to the first ionization continuum bands belonging to a Rydberg series related to a higher IP are found. The problem of its assignment is discussed.
1. Introduction It has been known since the works of Price and Wood [I], Wilkinson [2] and El-Sayed et al. [3] that Rydberg series are found in the spectrum of benzene both below and above the first ionization potential_ At frequencies lower than the first IP we find - in addition to the three well known x* + ir bands - Rydberg series of two types; (a) a series of the np type with a quantum defect of the order of 0.50, and (b) series having a low quatitum defect of about 0.05. The latter might be of the nd type in which case they are g ++ g
and forbidden by the Laporte rule or nf in which case they violate the approximate atomic selection rule, AL = 0, f l_ Both types of series converge to the lowest
trifluorobenzene
[14], penta- [12] and hexafluoro-
benzene [ 12, 131 have also been studied. The most interesting point is perhaps the following: whereas the
photoelectron spectra give clear evidence of the sp!itting of the elg orbital in derivatives having no threefold axis, the vacuum W spectra do not seem to be affected by this. The expected splitting of the allowed LElu + I Alg ?* + n band has never been clearly_observed. Furthermore, although under these lower sym-, metries ns and nd type series become allowed and there could be a greater number the series which were ungerade in benzene none of these have been shown to
c. . .. ’
exist. Only two Rydberg series (related to the lowest
II ionization potential (9.25 ev) which is related to the elg orbital [4]. The relative insensitivity of n electron energies to
IP) were found in all the fluorobenzenes examined so far and these are of the types described above: one with a high quantum defect (?I$) and one with a low quantum defect. (However, Smith and Raymonda [ 121 go not mention the np series for hexaflu&obenz@neJ
fluorine substitution ES-8 ] and the non-interference ofthe fluorine-A03 in the related part of the spectrum
The three lowest II% of fluorobkene (FB) are at 9.20 (ad), 9.56 (vert) and 11.7 (ad) eV [4]. Nthough
makes the study of the spectra of fluorobenzenes interesting:In a previous publication [9] from this labora-
in benzenejtself there might be a o level between the elg and aIu n leveis th&e is little doubt that in fluoro-
tory the bands due to valence-shell transitions in the vacuum ultraviolet spectra of aseries tif fluorobenzenes have been discussed. The Rydberg bands of monofluo.robenz&e (FB) have been studied by Hammond et al..
benzen&, wjth the:possible exceptiqn of FB, alI’n levelk are at e+rgies lower than the lowest u level. So .th$ _ -second IP of FB. resuI& from-th& splitting :o.fthe e’,, or-._.
’;
‘.-
Volume 27, number 4
CHEMICAL PHYSICS LETTERS
reassigned these bands to the n = 3 member of a series converging to the third IP with a quantum defect of 0.55. One o.f the alms of our work on the ditluorobenzenes has been to ascertain if similar bands exist in the spectra of the latter.
2. Interpretation
of the spectra
The photoelectron spectra of the three difluorobenzenes, henceforth designated as (1,4), (1,2) and (1,3) have been-measured prevIousIy by Baker et al. [15] , by Murrell and Narayan [ 161 and by KIessinger [17] _Our values differ only very slightly from theirs. Of interest to us are the three lowest IP’s of each compound which are: (1,4) : 9.18 (ad), 10.07 (advert), 12.12 (ad); (1,2) : 9.30 (ad), 9.93 (vert), 12.63 (vert); (1, 3) : 9.35 (ad), 9.94 (vert), 12.22 (ad). (ad = adiabatic, vert = vertical, advert = vertical and adiabatic.) The split in the elg IF of benzene is quite significant: O-67,0.43 and 0.42 eV in the above order. Figs. 1,2 and 3 show the absorption spectra and the numerical data are compiled in tables l-3. It is quite clear that aII three molecules possess the two usual Rydberg series converging to the lowest IP: one with a quantum defect of about 0.5 and another with about 0.05. In eachcase the vibrational fine structure of these
15 August 1974
bands is very similar to that found in the respective photoelectron spectra. The vibrational intervals are found, about 400-500,850--1000, and 1250-1450 cm-l. They are similar to those found for (I, 3,5) [14] and we shall not discuss them in detail. The lowest IP of (1,4) is at 74050 cm-l. At slightly lower frequencies, at 73700 cm-I we fmd a IocaIly prominent band. Since there is a similar band in the spectrum of (1,3,5) [14] we assign this band to the n = 3 member of a series converging to the third IP with a quantum defect of 0.86. [(I, 3,s) which has D3b symmetry has of course no “second” II’.] On the other side of the IP we found seven weaker bands, 74850,75600,76730, 77650,78200,78600 and 79030 cm-l_ This group of bands resembles those found in the same spectral range for FB. Following Smith and Raymonda [ 121 these bands should be interpreted as vibrational bands belonging to the transition with origin at 73700 cm-l. We made an attempt to interpret these bands as belonging to a series converging to the second IP. This is only possible, however, if we suppose that the lower members of the series are among the bands found in the dense 68000 cm-l region_ We have no real proof for this, however_ In (1,2) and (1,3) the situation is similar. The first IF is at 75020 and 75350 cm-l for (1,2) and (1,3), respectively. Close to these we find again one relatively intense band for both molecules (75200 and_ 75500 cm-l) which are readily assigned to the n = 3 member of a series converging to the third P. Going to higher
CHEMICAL PHYSICS LElTERS
Volume 21, number 4
llnmf 150
160
-_
74
FREQUENCY
1974
130
I40
70
66
62
1.5 Aue;ust
78
(cti’) x tCi3
Fig. 2. The Rydberg bands of 1,2-difluorobenzene.
X 0-m) 150
160
130
140
1
I 62
FREQUENCY
78
74
70
66
(cf&c
Id3
Fig. 3. The Rydberg bands of l,f-d.iflnorobenzene.
frequencies.~e spectrum of (I, 2) becomes diffuse but in that of (1,3) we fmd weaker bands at 75500,75800, 76500,76800,77100 and 77300 cm-l posing the same problem as in the case of (1,4). Now, it seems to be worth noting that the quantum defects are of the order of 0.85 for (I, 4), (I, 3, (I ; 3) ami (1,3,5) and Smith and Raymonda found 1. I.5 for penta- and hexafhrorobenzene. In all these cases the: series is tif the ns type, related to the aZu_IPof hen; Zen+. On the other hand Smith and Raymonda fourid-.’ _ &-I “p 6~ skies with a quantum defect &f 0.55 for
FI3. According to Koch and Otto [lSj , Jonsson and Lindholm [lQ] and Robin [20] a sharp Iine at 73880 cm-r in the spectrum of benzene itself can be assigned to &he3p f 3e2, transition, an dowed transition related to the lowest o iP. One possible explanation of the great difference between the quartturn defect of : : ti Q$er Rydberg series for FB and the more%eayy fluorini subst&itod detivatives of benzene that comes ... in mind.is t&it for FB the band is stiil related to a. ‘. IRydbGg se&j conv&gkg t.@the’lotiest ” I~Ai& [email protected], benzene i&If but.‘that in the dthorsjtis #at@ to that:
I’ . ._ .. : : 1._ps9.-. ;: _ .: ) .,, . ... -~.. . 1.. _:_ .. : . .‘.. ._. :,__ -.’ :.” .‘. .‘. ,.: : .: ‘.:.. . - ,.. _,’ .,’ : -:;_..‘:‘_~ :.. ‘_ _.,_ ,_ ;_.I ._;:: ,: -: -.-I f’-,,-.. .._._,.__‘“.‘_. _‘.” .:__-_;_ ._(. -:- ._‘. -- “_ : 1,;‘. - “.- -,. . . _. I... .: -,--.:.. ,-. ,I,:, .,. :.,. ._.;.: .:- :. .-y ,~. .. ,--. ‘,,:‘-,y:.r.;~.: :.:,:‘.,, “,e_., .’ :.,.T :_ ,‘-:::. ,,;.’ ;:-: .,.;-I, 2...,::.___: ; .,, ,, -1’ “‘.,-..__:‘,-. 1‘. :.y.:... ..,. _.,, ., _ ._..:.. .I 1:: ,:,..Z’ ; :.:“I ,-.; ?:;_‘;p. ._. ;::..,:_:.,L_‘.:.;i:__;,, ,,,:.,;;, _..~;:~‘:_,‘_,z~“ <,T’..:.; ._;._ ~:‘ :.;._-.-r._ __-_r_-,.~.. ,_;, .....__Y,, :,,~~-_.-.‘;: ,;_::.‘.,.:.,r.‘: ,_._‘.:‘,” ‘.:l.;.,;.~,I_,“--._ ; _.: .7.’ .:..“-’ :. .:, j ‘-ril” ‘._: ‘.I: ;;;r.k,T.:., ::i~,.~:~~._~.,5%,i~... ~:~~,;i.(.,.,:~:~,-..~~~~~~.~-~~~-~.~”~’:~~~ i., .:..‘..‘,.,>,-*. ;..‘.:; ,z_; :-. ‘._‘.’.-.‘2. .: ; .;:2.:_:: - : +.-)L.y,;,: ,.;;I;: ..:, .._ _.... .(-&<<’ L. i.~:.,l~:‘:~.~.--r.,__-“. ,._.‘. :: :-;;.,.m<,r.-. ,:.. . . . . :-.i’_. :’i .;-.:.:_..y <,.. _. -,1. ... ._ .-.,v %I’_ _5. .=__i-‘m.:: ,,_+._-;:,*;..,;l-;-. .. ~_id_i. ” 1T_.,--..:.-:.. T--.’ ‘- ’ ,.=;‘ .;.::; 1i j,:-<.;.:;+p=: .,,.. i.;_,y‘ .rr_<
:
:
.. 1..:. . . .,
.__ :.
:
.
..
CHEMICAL PHYSICS LElTERS
Volume 27, number 4
\
15 August 1974
Table 1
Observed and calculated frequencies of Rydberg bands ccmverghg to the lowest ionization Potential of 1.4-difluorobenzene. Vibrational iutexvals associated with Rydberg bands
+(obs)
n
bti’
1
Vibration
~&alC)
(cm-‘)
(cm-’ )
unkaIc) - u,(obs) (cm-‘)
61120 66790
-100
69380
+10
70770 71610 72150 72520 72780
+40 -20 +90 i-20 -150
56060 64840
-30
68430
+10
70240 71280
0 +90
Series R; A = 0.07 3 4
66890 67320 67740 68120 69370 69810 70730 71630 72060 72500 72930
5 6 7 a 9 10
430 850
1230 440
Series RI A = 0.52 3 4
64870 65220 65660 66090 66450 68420 68860 70240 71190
5 6 7
350 790 1220. 360 430
has been a-&r) in benzene.
3. Conclusions
The results can be summed up as follows: (i) All three molecules possess one Rydberg series of the np type and one of the nf or nd type, both converg&g to. the lowest STIP. These series seem to be characteristk of all fluorobepenes and probably many other benzene derivatives. (ii) Wecould not obtain 3 decisive argument settling the pr6blem of th& +&gnment of the ba@s found in *UVspe&u&in the.v&ix&ofthef%tIP.Thus, id least for the tin&being, weare &dy to kept t&e -_: ~&i
-, ,;_
:.
.: ;
.. ; . : :
._.
)
more conservative assignment of Smith and Raymonda relating these to the third and not the second IP. It is possible, however, that for benzene and FB this is a o IP while for the more highly fluorine substituted derivatives it is the higher n IP. A number of questions remain unanswered and would warrani further research. (a) WhatZs the reason that no ns type Rydberg series converging to the first IIFare found even though these become allowed under the lower symmetry of many of the derivatives? (Acttii Ailen and Schnepp [21] .found an extra btid. in the circular dichroism spectrum of some berkjtie~eri~atives which ‘k+ns to have thti right location
to be.tl&3s
+-elk b&d.):
-.
: .,.
..
(b) The s&6 question can be asked ~oncerning’so~e :
_. .~:
._
-.,. :.
:
15 August 1974
CHENfCAL PHYSLCS LR’lTRRS
Vohrme 27, number 4
Table 2 Observed and cahxlated frequencies of Rydberg bands converging to the Lowest ionization potential of 1,2-dithiorobenzene. tional intervals associated with Rydberg bands Vibration fern-r 1
n
v&slc)
Vibra-,
- vnfobs)
mf-‘1
SeriesRi A = 0.03 3
62910
-1150
68390
-10
70910
-30
72250
72270
i-20
73080
73090
+10
64060 64540
480 1010
65070
1500
65560 65960 4
400
68400 68930
530 1000
69400 69790 70300
1390 510
70880
5
71410
530
71910 6 7
1030
Series Rr A = 0.46 58350
3 66600
4
67130
70020
-20
-20
1000 1380
67980 1010
68140 70040 70540
-10
530
67600
5
66590
500 1020
71060
1370
(71410)
6
71790
71770
7
72780
72780
8
73510
73420
9
73820
73S40
+20
10
74150
74140
-10
:. : .‘ effect on thi ultraviolet spktk? ‘ AH that F be Hd tit $T present stagk 2j ‘A< n&my of $e i&ted observatikisare manif&;itio~~ of tJxe2. I:, “ff . uorokffect” thai is the stiti effect df flUo~e4i3~~‘:
np .and nd manifolds. ’ (c) If the above argument iS correct .why are no ,, : Ry$erg s@fs observed which coqverge to.$he second IP r&ult@g from-the split of -tie elg orbital bf benzene? a&&&l
members
_
refie+h
.;’
_, .,
W
little
of the
: fa)Ho~tOexplainthattht:sizeabfe.spfitofthee~g:~ -J&l
~~~~hotoelectr0~
-. : -_’ .,_ ..‘ ._. -1‘
I-‘.
spe*.hj=
-
-,. __..“.’
0 -90
:StitUdb~,OXl6,-$1&~@1~~~$$~~
~O~~~.~~~e~~~
pidfo@d Sect:_.iin u-eItktron [SY$] ‘.,‘.’ “(; ’ ;;. ___ ei&rgies -.... : ..._._., .,,_, ~ _::._ ,,__:~~ __I _,._ ..::-_ ..,_.,L _. .( ...-. ;.._.‘, ., : :.,j ;_ .i; _.,,:. .. _‘,..” : .: .,-.; ‘ _,. ._’,: ..,.:; ,:. i _’ . .. .‘-, ,:,. _.’ : .‘ .,-__ ..,,
~,_: ::.
CHEMICAL
Volume 27, number 4
PHYSICS
LETTERS
15
August 1974
Table 3 Observed and calculated frequencies of Rydbcrg bands converging to the lowest ionization potential of 1,3difluorobenzene. tional intervals associated with Rydberg bands Vibr$ion (cm 1
n
Qzdc) (cm-’ )
QxIc) - +obs) (cm_’ )
62330 67960
-20
70530
+20
71910 72750 73280 73650
+30 - +60
Vibra-
Series R; A = 0.06 3 4
67980 68300 68530 69010 70510 7’1060 71630 71880 72690
5
6 7 8 9
320 550 (1030) 550 1120
73520
+130
Series RI A = 0.54 3 4 5
6 7 8 9. 10
65250 69480 70030 70790 71290 72450 73150 73520 73819
56900 65860 69510
+610 +30
71340 72390 73050 73490 73800
+50 -60 -100 -30 -10
550 1310
Acknowledgement
[5] C.R. Brundle, M.B. Robin and N.A. Kuebler, J. Am.eem. Sot 94 (1972)
References [i] W.C. Price and R.W. Woo& J:C lem. Phys. 3 (1935).439_. [Z] P-G. wilkinson; Can. J. Phys. 34 (1956) 596.. ~[3] .M.F:A. El-Sayed, M. Kasha and Y. Tanaka, J. Chem. Phys. :3+ (1961) 334. .: .: _:. ..: ._ .I [4j D-w. Tume&C.-Baker, A.D; Baker and C.R. BrundIe, .j :” &fi&di~ photoeI&ti&i~~ectios~py (Intersc&tiw, New ..,.- York.19701 chs:i0 and 11. &d references therein. .
1451.1466.
[6] I.D. Clark and D.C. Frost, J. Am. Chem. Sot. 89 (1967) 244. [7] D-W; Turner, Tetrahedron Letters (1967) 3419. .[8] G. Bilanger and C. Sandorfy, Chem. Phys. Letters 3 (1969) 6.61. [9] R Gilbert, P. Sauvageau and C. Sandorfy, Can- J. Cbem. 50 (1972) 543. [IO] V.J. Hammond, W-C. Price, J.P. Teegan and A-D. Walsh, Disc&ions Faraday Sot. 9 (1950) 53.. [ 1l] .R. Gib&t_and C. @ridorfy, &em. Phys. Letters 9 (1970 121. -[12] D:R..Smith and’J.W:.F&ymonda, Cherp;Phys. L&t&s 12
We acknowledge financial help from the National Research Council of Canada and a postgraduate scholarship to one of us (R.G.).
..
(1971)
269.
.[131.C. Slusc-Goffart and J_‘Mo&ny, .. .-. ‘_-:, ... (l?j&).2jl_-. :
.-
:
:
_-
.; _. _, _I _.
.:
(3h&:Ph$s.
Let&
25
Volume 27. number 4
CHEMICAL PHYSfCS LEkT.ERS
f 141 R, Gilberr, P. Sawageau and C. Ssndorfy, Chem. i%ys_ Letters 17 (1972) 465. [IS] A.D. Baker, D.P. hfay and D_W. Turner, J, Chem. Sot. B (196fs) 22. [16] B. Narayan and J.N. Munell, Mot. whys. 19 (1970) 169. [l? j M. Klessinger, Anger- Chem. 11 (1972) 525.
15 Axsgust1974
w-1 B.O. Jonssonand E. Lindholm, Ark& Fysik 39 (196% 65. M.B. Robin, Higherexcited states of po!y?tomic moleIX&S, Voi, 2 (Academic Press, New-York, 19741. S. Allen and 0. Schnepp, J. Cbem. Pbys., ta be publisbdd.