1200
The Journal of Physical Chemistty, Vol. 83, No. 9,
Goodman et al.
1979
(18) J. F. Stevens, Jr., P. S.Engel, and R. F. Curl, Jr., paper WM3, Sixth Austin Symposium on Gas Molecular Structure, Austin, Tex., March 3, 1976. (19) E. Flood, P. Pulay, and J. E. Boggs, J. Mol. Struct., 50, 355 (1978). We are grateful to Professor Boggs for making this manuscript available to us prior to publication. (20) L. D. Fogel and C. Steel, J . Am. Chem. SOC.,98, 4859 (1976). (21) S. F. Nelsen, J . Am. Chem. Soc., 96, 5669 (1974). (22) J. E. Anderson and J. M. Lehn, J. Am. Chem. Soc., 89, 81 (1967). (23) The vapor pressure data used to estimate the boiling point of cisdimethyldiizene were not presented in our earlier communication.'0 This data and the procedure used to obtain it are given in the
(24) (25)
(26) (27)
Experimental Section of the current paper. The melting point was done by the Stock method. W. J. Hehre, J. A. Pople, and A. J. P. Devaquet, J. Am. Ctmm. Soc., 98, 664 (1976). The calculated frequencies for the EE and SS conformers were not identical because two of the interaction constants transferred from the trans isomer were specific to the NCH bending coordinate for the in-plane CH bond. R. N. Camp, I. R. Epstein, and C. Steel, J . Am. Chem. Soc., 99, 2453 (1977). J. F. Stevens and R. F. Curl, Jr., private communication.
Vibrational Assignments for the Raman and the Phosphorescence Spectra of 9,lO-Anthraquinone and 9,lO-Anthraquinone-d,' Kevin K. Lehmann,' John Smolarek, Omar S. Khalil,3 and Lionel Goodman* Department of Chemistty, Rutgers, The State University of New Jersey, New Brunswick, New Jersey 08903 (Received November 8, 1978)
The Raman spectra of 9,lO-anthraquinone (AQ) and 9,lO-anthraquinone-d8 are examined. Raman band assignments are made from this data and from a published normal coordinate analysis. The Raman spectra of AQ at 5 K is reported and vibrational assignments for the phosphorescence spectra of AQ in n-hexane at 4.2 K are reexamined in light of new 3B1, *A, phosphorescence data. Contrary to previous work from this laboratory, it is concluded that although higher order vibronic interactions may he operative between the two closely spaced 3AU-3B1gelectronic states, these interactions are not manifested in the phosphorescence spectra of AQ in n-hexane at 4.2 K.
-
I. Introduction 9,lO-Anthraquinone (AQ) has become an important model to study vibronic interactions and possible breakdown of the Born-Oppenheimer approximation due to possible interactions between the lowest excited state (3B1,) with the nearby 3Auand 3Bluelectronic states. The low temperature, high resolution phosphorescence spectra of AQ require firm assignment of the vibrational bands in the ground state. Vibrational spectra of AQ have been studied using IRG8 and Raman s p e c t r o s ~ o p i e s . ~The - ~ ~Raman spectra were obtained on a powder a t room temperature and were tentatively assigned on the basis of a normal coordinate analysis (NCA). In this paper we report a new study of the Raman spectra of AQ and of its perdeuterated analogue AQ-ds. Raman data for AQ and AQ-d8 at -300, -100, and -5 K and the normal coordinate analysis are used to assign the Raman bands. We also report new phosphorescence data on AQ in n-hexane at 4.2 K. We use the Raman band assignments and the published IR data to reanalyze the phosphorescence spectra. The new analysis solves questionable assignments and some basic questions on vibronic effects in the phosphorescence spectra of AQ in n-hexane. 11. Experimental Section AQ and AQ-ds used in this study were zone refined under an argon atmosphere. AQ-ds was synthesized by oxidation of anthra~ene-d,,.'~ Raman spectra were run on a Cary 82 spectrometer using the Kr+ 6471-w line. Laser power was 100 mV at the sample. Polarization spectra were run with the Ar+ 5145-A line in order to minimize polarized absorption. The spectral band width was 1 cm-l except for the polarized
-
0022-3654/79/2083-1200$0 1.OO/O
TABLE I: Low F r e q u e n c y R a m a n Spectra ( c m - ' ) of AQ ref 10 t h i s s t u d y ___ r e f 11 (5K) 83K RT' 38 36 27 (a,) 30 63 63 51 (a,) 54 65 63 57 ( b g ) 60 74 73 66 (a,) 68 83 92 92 82 ( b 1 145 150 148 150 156 a RT denotes r o o m temperature.
(Pg)
spectra which were run with a 3-cm-' band width. The low solubility of AQ made it impossible to obtain solution spectra, even by using a saturated solution in benzene at its boiling point. AQ has a melting point of 285 "C and is stable to 300 "C. However, local heating due to laser line absorption was enough to cause decomposition at the melting point. The decomposition product's fluorescence swamps the Raman spectra. Raman spectra of AQ and AQ-ds powders at room temperature at 100 and a t -5 K were obtained using a capillary tube, a Harney-Miller cell and cold Nz gas, and an Air Products liquid helium Helitrans cryostat, respectively. The phosphorescence spectra of AQ in n-hexane at 4.2 K was run as previously described4 except for the excitation source which was the 3371-A line of a Molectron UV400 pulsed nitrogen laser.
-
11. Results and Discussion A . Raman Spectra. The low temperature Raman spectra, 0-160 cm-l at 5 K, are shown in Figure 1. Five bands are observed below 100 cm-l and two bands are 0 1979 American
Chemical Society
Vlbrational Spectra of Anthraquinone
The Journal of Physical Chemistry, Vol. 83, No. 9, 1979
1201
TABLE 11: Assignments of the Raman Active In-Plane Vibrations (cm-I ) of 9,lO-Anthraquinone -AQ-h, AQ-d8 deuteration shift ag
'12
V11 '10
9' 'R
VI '6 V5 v 4 v 3 V2 VI
b3,
v33 v32 '31
'30 '29
V28 V21 '26 '2 5 "24
'23
a
obsd"
calcdb
obsd"
calcdb
obsd"
301 47 5 684 1144 1030 1178 1212 1317 1596 1665 3067 307 5
322 50 3 686 1031 1149 1185 1323 1476 1559 1714 3050 3075
289 47 5 645 854 814 1095 (1203)' (1203) 1569 1660
312 496 685 829 850 1102 1307 1379 1526 1700 2280 2287
12 0 39 290 216 83 9 114 27 35
(250) 364 67 8 924 (1082) (1308) (1326) (1584) (1653) 3043 3082
27 5 378 705 9 39 1124 1227 1382 1500 1628 3057 3076
234 351 651 901 (830)
27 2 355 67 9 916 85 6 1006 1268 1438 1612 2280 2288
14 13 27 23 252
This work, 5 K powder spectra.
Calculated, ref 12-14.
(1208) 1561
calcd 10
7 1 202 299 83 16 97 33 14 770 788
3 23 26 23 268 22 1 114 62 16 777 818
118 23
' Denotes marginally detected bands. TABLE 111: Assignments of the Raman Active Out-of-Plane Vibrations (cm-l ) of 9,lO-Anthraquinone deuteration AQ-h, AQ-di shift ___--
obsd" calcdb obsda calcdb obsd" calcdb b,, v 1 6
239
vis 440 v 1 4 770 v , ~ 978?
bzgvzz vl1
vz0 v19 V I R
vl1
156 419 449 654? 819 990?
232 464 733 939
224 389 609?
220 401 591 808
15 51 161
12 63 142 131
219 409 482 713 847 941
143 410 400
207 408 444 704 639 809
13 9 49
12 1 38 9 208 132
599
" This work, 5 K powder spectra.
I,
220
Calculated ref 12-
14.
IA 150
Flgure 1.
I00
50
Cm-'
Raman spectra of AQ-h, in the 0-150-cm-' region at 5 K.
located a t 150 and 156 cm-'. The data are compared to that of Miyazaki andl ItolO and of Rasanen and Stenmanll in Table I The 148-cm-l line, reported by Ito as having a preferential B, polarization and assigned as a combination of 66 and 82 cm-l, splits into two lines at 150 and 156 cm-' at 5 K. The 66-cm-l line shifts to 74 cm-' while the 82-cm-I line shifts to 92 cm-l at 5 K. This leads to a frequency sum of 166 cm-' for this combination thus eliminating that possibility. Combination of the 60 + 83 cm-l and 68 + 83 cm-' lines, which give good agreement in the room temperature spectra (145 and 150 cm-l), becomes 157 and 166 cm-' at 5 K, hence, also negating them as possible combinations. Two possible explanations remain. First, these two lines are combinations of the 63 92 and 65 92 cm-I lines in the low temperature spectra which gives a good numerical
+
+
agreement with one combination but not the other. Second, these lines are factor group splitting components of a molecular vibration. The second possibility was deemed invalid by Rasanen and Stenmanl' because these lines are wider than other AQ molecular lines and because of the observation that the strong lines at 150 cm-' in naphthaquinone and in anthrone crystals disappear in solution or in melts. Our line width measurements at 5 K do not show a difference between the 150- and 156-cm-l pair and molecular lines. The assignment of these two lines as a lattice combination is plausible but uncertain. Furthermore the deuteration shift (9-10 cm-') for these bands is much too large for lattice modes. The (rn(AQ)/rn(AQ-d8))1/2= 1.02 factor for lattice modes predicts only a 3-cm-' isotope shift. Hence we assign the 150/156-cm-' pair as a factor group split molecular band. The Raman data at higher frequencies agree essentially with that of Rasanen and Stenman,l' but differ from that published by Singh and Singh6 who observe several additional intense lines. These lines are definitely due to impurities. The Raman active molecular vibrations of AQ (in-plane 12 ag and 11 b3g; and out-of-plane 4 bl, and 6 bSg)are
1202
The Journal of Physical Chemistry, Vol. 83, No. 9, 1979
Goodman et al.
TABLE IV: Assignment of the IR Single Crystal Spectra of 9,lO-Anthraquinone (cm-l) AQ-h, au
v34
obsda
calcdb
obsda
calcdb
1010
800 755 638
816 728 640 446 135
210
750
9 40 850 7 37 492 146
112
124 122 97 46 11
3080 3040 1681 1594 1455 1310 1304 1168 (1053) 40 I 236
307 6 3057 1698 1607 1460 1296 1175 1124 818 507 208
2295 2275 1676 1568 1400 1120 1021 872 (8951 39 5 222
2288 2280 1697 1579 1357 1015 1171 8 69 7 66 481 197
785 165 5 26 55 190 283 296 158 12 14
788 777 1 28 103 281 4 255 52 26 11
3075 3045 1576 1475 1330 1285 1205 1145 9 35 624 390
3074 3050 1597 1477 1392 1307 1158 1041 959 618 37 7
2295 2279 1550 1405 1310 1243 955 828 922 601 382
2286 2276 1558 1412 1339 1271 854 811 9 30 587 376
780 765 26 70 20 42 250 317 13 23 8
788 774 39 65 53 36 304 230 29 31 1
967 798 67 1 47 2 339 137
845 743 562 398 348 160
813 724 555 411 337 128
125 72 131 92 27 7
94 74 116 61 2 9
v37 '38
b1U
v39 '40
'41 '42
v43 '44
V45 '46
v47 '48
'49
b*u v 5 0 v51 '52
'53
'54 '55
'56 ' 5 7
'58 '59
'6Q
b3U ' 6 1 '62
'63 '64
'65 '66
Reference 7.
,
deuteration shift
calcdb
'35 36
AQ-d,
obsda
970 815 69 3 490 37 5 167 References 12-14.
assigned in Tables I1 and 111. IR vibrations are listed in Table IV with the Mulliken notation used throughout. Assignments are made by comparison with AQ-d8and with the NCA. In the 100-500-~m-~ region, NCA predicts nine fundamentals, seven ring deformations, and two C=O modes; nine are observed, counting the 150/156-cm-l pair as one band. The unpolarized bands at 156 and 419 cm-l are assigned b2 the perpendicularly polarized bands at 239 and 440 cm-T are assigned to bl,. All are in good agreement with the calculated position and with isotope shifts. The bands at 250 and 449 cm-l are tentatively assigned as b3g and b2ginstead of possible factor group pairs of the 239and 440-cm-l bands, respectively, even though the isotope shifts within the pairs are identical. The latter assignment would leave two missing bands in this region. The 301and 364-cm-l bands are assigned ag and b3 , respectively, since this order agrees better with NCA. $he very strong band at 475 cm-l is assigned to ag (ull). Five fundamentals are calculated in the 600-850-cm-l region; seven bands are observed. The strong pair of parallel polarized bands at 684 and 676 cm-' shift to 654 and 652 cm-l, respectively, on deuteration based upon their intensities. The more intense 684-cm-l band is assigned to ag (vl0) and the less intense 676-cm-' band to b3g(ual). The band at 770 cm-l is perpendicularly polarized and assigned to uI4 (big). The band at 795 cm-l is assigned to an impurity since Singh and Singh observed a relatively strong signal at this frequency. The room temperature band at 819 cm-l is unpolarized and splits into two bands at 817 and 820 cm-I at 5 K. This band is assigned as a b2gfundamental. It is identified with one or both of the 592/599-cm-l pair in AQ-d8 giving an
isotope shift in agreement with NCA calculation. In the 900-1130-~m-~ region five bands are predicted. The very intense band at 1030 cm-l is the % (u8) mode and is assigned to 814 cm-l in AQ-d8. The strong parallel polarized band at 924 cm-l is assigned to bSg ( u ~ and ~) identified with the 901-cm-' band in AQ-d8, in close agreement with NCA. The b3g( ~ 2 9 )mode is assigned to the slightly parallel polarized 1082-cm-' band in AQ and the weak 830-cm-' band in AQ-$. The bands at 978 and 990 cm-l are tentatively assigned to blg and bZgvibrations, respectively. In the 1140-1350-cm-' region, six fundamental vibrations are predicted. Twelve bands are actually observed, but four are marginally detectable (Table V). Ignoring these and obvious combinations the 1144-cm-' band in AQ and the 854-cm-l band in AQ-d8 are assigned to age(ug) in close agreement with NCA. The 1173/1178-~m-~ p a r is assigned to a factor split ag (u7) fundamental, identified with the 1087/1095-~m-~ pair in AQ-d8. The bands at 1212 and 1317 cm-' in AQ are assigned to ap. The bands at 1308 and 1326 cm-' are both tentatively assigned to bSg. Four fundamentals are predicted in the 1400-1860-~m-~ region. The very intense band at 1665 cm-l is assigned to the ag C=O stretching mode ( u J . The ag fundamental (u4) is assigned to the strong lines a t 1596 (AQ) and 1569 cm-' (AQ-d8). Firm assignment of weak b, modes in this region is difficult due to the large number of combination bands possible in this region. Complete analysis of the Raman spectra of AQ a t 5 K is given in Table V where all combinations are listed. The very weak bands observed by Ranasen and Stenman at 211, 226, 258, 575, 917, 1243, 1440, and 1480 cm-' are absent at 5 K but appear close to twice the noise level a t
The Journal of Physical Chemistry, Vol. 83, No. 9, 1979
Vibrational Spectra of Anthraquinone
500
30 0
400
1203
DO cm-’
200
Flgure 2. Raman spectra of AQ-hs in the 100-500-cm-’ region: (A) 5 K, (B) 100 K, (C) room temperature.
Figure 3. AQ-h, phosphorescence spectra: slowly cooled,
M in n-hexane at 4.2 K.
I ,
s
I
m
w
4800
4750
Figure 4. AQ-h8 phosphorescence spectra: fast cooled,
4700
4650
4600
M in n-hexane at 4.2 K.
room temperature. We conclude that these lines are not intrinsic to AQ and discard any assignments based on them. A portion of the Raman spectra of AQ (100-500 cm-’) a t -300, -100, and -5 K is shown in Figure 2. The increased splitting of the 150-cm-l line upon decrease in temperature is shown. B. Phosphorescence Spectra. The lowest electronic
state of AQ has been assigned as a 3B1,435which gains intensity through vibronic coupling with an upper state via blu, bZu,and bSuvibrations. Analysis of the spectra was based on the IR ground state vibrational frequencies by Pecile and Lune113 and new Raman data. The IR spectra have since been reassigned by Gazis, Heim, Meister, and Dorr7 (reproduced for convenience in Table IV). The
1204
Goodman et al.
The Journal of Physical Chemistry, Vol. 83, No. 9, 1979
TABLE V: Vibrational Analysis of the Raman Spectra of 9,lO-Anthraquinone Powder a t 5 K v , cmre1 int assignment 38 63 65 74 92 150 156 239 250 302 364 418 421 440 449 475 654 67 6 684 770 793 795 817
15 29 26.7 17 3.5 1.7 4.1 4.1 4.7 1.5 2.1 0.23 0.17 0.87 0.92 12.2 0.4 2.0 7.0 1.85 sh 0.06 0.4
820 900 924 978
0.6 0.2 1.2 0.5
992 1006 1014 1023 1030 1082 1100
0.52 0.23 0.7 sh 21.0 0.6 0.2
1144 1164 1173 1178 1206
19.0 0.2 8.7 31.4 sh
v,(1
cm-I
u14;
t u s , = 791; b,, u d 0 t u 4 , = 797;b3, u~~ t v , =~ 813; b,, or 2 x u,, = 814 V I , ; bz, u , , t u6,= 897 b3g
'30;
2x
u6, =
1.2 0.6
1243 1308 1310
0.2 0.7 sh
1318 1326 1400 1429 1450 1460 1479 1560
2.3 0.35 0.2
1570 1580 1584 1596 1631 1634 1640 1650 1665 1702 1738
980 or
u I o t u I z = 985; A, u,, t v s 9 = 996; b,, u , , t u l , = 1004; a, u j 9 t u~~ = 1014; a,
ag u , t~ u 6 2 = 1083; b,, u,, + u s 8 = 1102; b,, or v 4 , + u , , = 1100; b,, v , ; a, u,;
u,;
a,
u 6 , t u b U= v6;
1205; b,, or
t u , , = 1206; b,,
u,,
1212 1217
ag
u , t ~ u4, = 1220; b2, or u , , t u h 2 = 1220; b,,
u , t ~ u,, = 1310; b,, u d 6 + u j 7 = 1312; b,, or v F St u j , = 1310; b,, u , ; a, uq7
+
~
6
=6 1428; b2g
u , ~t u j , = 1452; b,,
0.6 0.2 0.2 sh 2.4 20.0 0.3 0.3 0.8 100.0
TABLE VI: Vibrational Analysis of the Phosphorescence Spectrum of 9,10-Anthraquinone-h, in n-Hexane at 4.2 K ground state vibrnC
+ u 6 , = 1477; b,, u , t~ u,, = 1558; b,, or v j s t u,, = 1559;a,
u,,
u,;
a,
uj,
+ u6,=
2x
u B Z = 1630;a
u d 6 t u S 2=
1635;Pbl, 1642; b i g
v , ; a, totally symmetric C=O str u , ~ u s , = 1705; b,,
+
0.2
availability of the new ground state vibrational data discussed in section IIIA warrants a new vibrational analysis of the phosphorescence spectra. Further, in the n-hexane 4.2 K phosphorescence spectra,
21 783 21 763 21 743 21 724 21 707 21 616 21 555 21 529 21 371 21 266 21 259 21 1 8 5 21 1 6 3 21 140 21 096 21 089 21 078 21 058 20 992 20 970 20 838 20 796 20 628 20 613 20 520 20 490 20 476 20 463 20 444 20 432 20 421 20 327 20 301 20 288 20 204 20 198 20 180 20 152 20 101
Av,
cm-'
assignmentb
0 20 40 59 76 167 228 254 412 517 524 598 620 643 687 694 7 05 725 791 8 13 945 987 1155 1170 1263 1293 1307 1320 1339 1351 1362 1456 1482 1495 1576 1585 1603 1631 1683
0-0; principle site 0-lattice 0-1at ti ce 0-lattice 0-lattice 0-u,,; o p skeletal def 0 - v , , ; ip skeletal def 0 - u ,,-lattice 0-06 6 - ~I 6 ; 0-b 3U-b,g site; 0-620 t 1 0 3 site; 0-620 t 96 O - V ~ , - U , ,O-b3g-bIu ; O-v,, 0 - u ,,-lattice site; 0-791 + 104 site; 0-791 t 96
v,
cnl-.___
167 236
62 6
O-'63
708
0 - u , ,-lattice O-uSz;skeletal def
816
0-u,,-lattice 0 - u , ,skeletal ; def 0-u3 2 - ~ 0-b 3g-b l u 0 - u s , ; CH bend 0-u,,; ring str 0-u , o-u,, 4
0-u,,;ring str site; 0-1456 t 105 site; 0-1456 t 92 0-u,,; ring str 0-u,,-lattice 0-u ,-u ,o; 0-b 3u-ag 0-u,,; ring str 0 - u , , ; ring str 0-v,,-lattice 0-v,,-u,; 0-bju-ag 0-u,, ; assymetric C = O str 0-u,,-lattice
935 1145 1168 1304 1310 1330 1455 1576 1594 1681
20 077 1706 19 873 1910 19 836 1947 19 818 1965 19 738 2045 O - U , , - U3 2 ; 0-b lu-b 3u 1 9 714 2069 0 - U,-v, 3 2 -lattice 19 486 2297 O-U,,-U,;O-b2,-ag ,; 19 307 2476 O - U , ~ - U0-b,,-a, ~ 19 292 2491 0-u,z - ,-lattice 1 8 945 2838 0-u,,-u ,;0-b , -ag 18 922 2861 O-U,,-U,-lattice 18 836 2947 0-u,,-u ; 0-b 2 u-ag 18 644 31 39 O-U,,-U,;0-b,,-a, 18 544 32 39 site; 0-3345 t 1 0 4 18 537 3246 site; 0-3345 + 96 18 517 3266 O-U,,-U 3 ; O-blu-ag 1 8 510 377 3 18 505 3278 1 8 4 7 2 3311 18 438 3345 0-u,,-u,; 0-b,,-a, 18 414 3369 0-v,,-u,-lattice 1 8 072 3711 O - U ~ ~ - U ~ - U ~ ~ bIU bIU 1 7 824 3959 0 - u 4 , - 2 X U , 1 7 713 4070 bIU 17 286 4477 O - I J , ~ - V ~ - U ~ Assignments are based on a Vacuum corrected. Single cround state vibrations of ref 7 and this work. crystal IR frequencies at room temperature.
the possibility of combination bands involving three quanta of a bl, mode at 687 cm-' was raised. This band was
The Journal of Physical Chemistry, Vol. 83, No. 9, 1979
Quenching of Benzene Fluorescence
1205
cation from this laboratory, they were assigned as 3 X u49 made possible by higher order vibronic coupling mechanisms. We conclude that although these higher order vibronic interactions might exist, they are not manifested in the phosphorescence spectra of AQ in n-hexane at 4.2
interpreted as evidence for nonadiabatic interactions. Other bands at 517,524,1263,1293,1351,1362,1947,1965, 3239, and 3246 cm-' could not be interpreted. We reexamined the phosphorescence spectra of AQ in n-hexane at 4.2 K using different concentrations and cooling rates. Figure 3 shows the high energy region of the phosphorescence spectra of 1 X loT5M AQ in n-hexane slowly cooled by hanging the sample in an inner liquid nitrogen cooled dewar and then slowly adding liquid helium. Figure 4 shows the phosphorescence spectra of 1X M AQ in n-hexane. Rapid cooling was affected by immersing the sample directly into liquid helium. The 517,524-cm-' and 687,694-cm-l pairs are enhanced in the concentrated, fast-cooled sample. This secures their assignments as secondary sites. The 517-cm-l line is separated from the strong 620-cm-l line by 103 cm-l and the 524-cm-' band is separated from the 620-cm-l one by 96 cm-l. These spacings are preserved for the 687- and 694-cm-' mode from the strong 791-cm-l (b3J mode and the 1351/1362-cm-l pair from the medium intense 1456-cm-l line. All. others are accounted for and the modified vibrationd analysis of the AQ phosphorescence in n-hexane at 4.2 K is given in Table VI. The data presented in this section show the 687- and 694-cm-l bands as [secondary sites. In a previous publi-
K. References and Notes (1) Supported by National Science Foundation Grant CHE 76-23813. (2) Taken in part from the senior thesis of K.K.L., Rutgers University, 1977. Department of Chemistry, Harvard University, Cambridge, MA. Abbott Diagnostics, Dallas, TX 75247. 0. Khalil and L. Goodman, J. Phys. Chem., 80, 2170 (1976). K. Drabe, H. Vesnvliet, and D. Wiersma, Chem. Phys. Lett., 35, 469 (1975). S. N. Singh and R. S.Singh, Spectrochim. Acta, Part A , 24, 1591 (1968). E.Gazis, P. Heim, Ch. Meister, and F. Dorr, Spectrochlm. Acta, Part A , 26, 497 (1970). C. Pecile and B. Lunelli, J . Chem. Phys., 46, 2109 (1967). F. Stenman, J. Chem. Phys., 51, 3413 (1969). Y. Miyazaki and M. Ito, Bull. Chem. SOC. Jpn., 46, 103 (1973). J. Rasanen and F. Stenman, Phys. Fenn., 10, 183 (1975). N. Strokach, E. Gastilovich, and D. Shigorin, Opt. Spectrosc., 30, 22 (1971). N. Strokach, E. Gastilovich, and D. Shigorin, Opt. Spectrosc., 31, 30 (1971). N. Strokach, E. Gastilovich, and D. Shigorin, Opt. Spectrosc., 30, 238 (1971). G. M. Badger, J. Chem. Soc., 764 (1947).
Quenching of Benzene Fluorescence in Pulsed Proton Irradiation. Temperature Dependencet M. 1.. West" and J. H. Miller Radiologicai Physics, Baftelle Pacific Northwest Laboratories, Richiand, Washington 99352 (Received November 21, 1977; Revised Manuscript Received January 8, 1979) Publication costs assisted by the US. Department of Energy
Dilute solutions of benzene in cyclohexane were irradiated with subnanosecond pulses of protons and changes in the time-resolved emission are studied as a function of temperature. Measurements were also made for ultraviolet excitation and the activation energy for quenching by solvent perturbations is compared to other values reported in the literature. An analysis of the radioluminescencedata based on dynamic quenching of excited states by proton induced free radicals suggests that most of the temperature dependence is from thermally activated solvent perturbations present under both proton and ultraviolet excitation. The experimental measurements are compared to model predictions and the temperature dependence of model parameters is discussed.
The study of fluorescence from excited molecules provides a useful technique for investigating the transport and transformation of energy in condensed systems. Pulsed radioluminescence, in particular, can be used to probe the early physical-chemical events following deposition of ionizing radiation. In an earlier publication,l we reported on the fluorescence decay of benzene in cyclohexane for proton and ultraviolet excitation and found the decay for proton excitation to be nonexponential. The decay for proton excitation was shown to be consistent with an intratrack quenching from radicals that were created along the individual particle tracks. In a more recent study,2 we developed a model for this intratrack quenching which included radical recombination as well as diffusional 'This paper is based on work performed under United States Energy Research and Development Agency Contract EY-76-C-06-1830. 0022-3654/79/2083-1205$01 .OO/O
expansion of the track core to explain the observed decrease in quenching rate with increasing time. Fluorescence decay was studied for incident proton energies of 0.3-1.9 MeV and the energy dependence of model parameters was shown to be a consequence of the energy dependence of the incident proton stopping power. In this paper, we report on a further investigation of this quenching mechanism through a study of the temperature dependence of fluorescence decay. Fluorescence response curves are obtained for both protons and ultraviolet excitation. Our UV measurements are compared to other values reported in the literature. We then discuss the temperature dependence of model parameters and make a comparison to the experimental data. Experimental Section The experimental apparatus is the same as that discussed in previous publications.l>* Subnanosecond proton
0 1979 American
Chemical Society
