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Towards the gas-phase UVVIS absorption spectrum of C60
17 June 1994
ELSEVIER
CHEMICAL
Chemical Physics Letters 223 (1994) 159-161
Towards the gas-phase UV-VIS absorption spectrum of &-, J. CatalAn Departamentode QuimicaFisica Aplicada,UniversidadAutbnomade Madrid, CantoBlanco, 28049 Madrid, Spain Received 2 1 March 1994
By analyzing the UV-VIS spectra for Cm in a series of n-alkanes, the positions of the absorption peaks in the corresponding gas-phase Cso spectrum were estimated from linear relations between the former positions and the corresponding Lorenz-Lorenz functions for the solvents.
1. Introduction Ever since large carbon clusters were found to be highly stable in 1985 [ I], much work has been devoted to investigating the electronic states of buckminsterfidlerene (CL&, promoted by the recent availability of macroscopic amounts [ 21 and the interest in checking for its presence in interstellar space. Recently, Hare and Kroto [ 3 ] suggested that certain signals detected in the so-called ‘diffuse interstellar bands’ [ 4-61 and the unidentified 2 17 nm band [ 79] might belong to CsO. Checking this hypothesis would be much easier were the gas-phase UV-VIS spectrum of C& available; however, this is not the case because the amount of required for the spectrum to be recorded could only be obtained by substantially raising the working temperature #l. On the other hand, several UV-VIS spectra for Cao in various solvents have indeed been recorded including those in dilute n-hexane [ 1I-141, cyclohexane [ 15 ] and methylcyclohexane [ 16 ] at room tem-
*’ When temperature reaches 700 K, C, vapour pressure in the equilibriumwiththepuresolidisonly4.12x1O-3Pa[1O],which is equivalent to a concentration in the gas phase of practically 7x lo-‘OM.
perature; those in methylcyclohexane [ 161, 3methylpentane and mixtures of the two [ 16,171 at 77IQthatinanargonmatrixat4K [18];andthe 375-415 and 595-635 nm regions for a sample that was supersonically cooled by using the resonant twophoton ionization (R2PI) technique [ 17 1. Recently, Renge showed [ 191 the possibility of precisely determining the position of the O-O component of a chromophore in the gas phase from the relation between such a position in a series of n-alkanes and the corresponding values for the LorenzLorenzfunction,f(n2)=(n2-l)/(n*+2),wheren is the refractive index. Based on this finding, in this work we approached the gas-phase UV-VIS spectrum of Cm by analysing its spectra in a series of nalkanes. The analysis was applied not only to the O-O component, but also to all those spectral peaks that can be detected precisely in order to subsequently predict the gas-phase spectrum for C6,,.
2. Experimental Spectra were recorded on a Cary 5 W-VIS spectrophotometer using a matched pair of cuvettes that were thermostated at 25°C. The C,, sample used was
0009-2614/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDZOOO9-2614(94)00448-Y
J. Catakin/Chemical PhysicsLetters223 (1994) 159-161
160
of the same purity as that employed in ref. [ 16 1. The n-alkanes used as solvents were all of spectroscopic grade and a high purity ( > 99%). CsOsolutions were made at a concentration of x 1 x 1O-’ M.
3. Results and discussion Table 1 lists the positions (in nm) of the 13 most representative peaks in the UV-VIS spectrum of C6,, in the different n-alkanes tested. The nomenclature
Table 1 Absorption spectra of C, in n-alkanes and in the gas phase: band wavelengths Band code ’
Band wavelength n-pentane
TO r2 A 73
t b A0 Al A3
C E G
619.4 591.2 589.4 567.8 540.6 427.4 421.8 407.8 403.8 390.6 328.3 256.2 210.0
’ Ref. [141. b See text.
(nm)
n-hexane
620.0 598.0 590.3 568.0 541.3 427.8 422.1 408.2 404.0 391.0 328.4 256.6 211.0
n-heptane
620.4 598.4 590.4 568.4 542.0 428.0 422.6 408.2 404.2 391.2 328.4 256.6 211.2
n-octane
620.4 598.4 591.0 568.6 542.4 428.0 422.6 408.4 404.4 391.2 328.6 256.8 212.0
n-nonane
621.0 598.8 590.6 568.6 542.8 428.2 422.8 408.6 404.4 391.4 328.8 257.2 213.0
n-dodecane
621.4 599.4 592.2 569.6 543.6 428.4 423.0 408.6 404.8 391.6 329.0 257.4 213.4
n-pentadecane
621.6 599.5 592.2 570.4 543.8 428.6 423.4 408.8 404.8 391.6 329.2 257.6 214.0
gas phase predicted b
exp. c
607.3 + 0.2 583.7f0.2 574.3+ 0.2 554.2kO.3 522.9fO.l 421.4fO.l 413.6fO.l 402.850.1 397.9fO.l 385.3kO.l 323.1 +O.l 248.750.1 190.0f0.2
607
402.4 398.0 385.7
“Ref. [17].
zoo
500
800
Wavelength
Fig. 1. Absorption spectrumof&,in (forbandcodeseeref. [14]).
n-heptane solution. (a) 200-800 nm. (b) 370-450nm;
(a)X20;
and (c) 415-8OOnm; (a)X 180
J. Catakin /Chemical Physicstitters 223 (1994) X5%161
used was originally proposed by Leach et al. [ 15 I. Fig. 1 shows the positions of the most readily identifiable peaks in the spectrum of CM in n-heptane, which are analysed below. As can be seen, there was good correlation between the positions of the spectral peaks (in cm-‘) and f( n2); the mean correlation coefficient was 0,976 and the predicted peak positions were subject to relatively small errors (less than 0.3 nm). It is interesting to note that the prediction for the O-O component (607.3 f0.2 nm) is quite consistent with the value obtained by Smalley and coworkers [ 18 ] for a supersonically cooled sample ( 607 nm), and so are the positions of peaks A,,, A, and Aj. In addition, because no substantial changes in the relative intensities of the peaks obtained for C&, in the different n-alkanes were observed, such intensities must be roughly similar in the gas-phase spectrum. Accordingly, our predictions must be faithful reproductions of the peaks in the gas-phase spectrum of Cm. The shifts in the high-end peaks from n-hexane to the gas phase are not constant, but vary between 330-470 cm-‘; others, such as peak 6i, are shifted by 650 cm-‘, and still others such as C, E and G are shifted much more markedly (by 500,120O and 5000 cm-‘, respectively). It is interesting to note that peak G is shifted so strongly that it is pushed into the vacuum UV region. This is consistent with the information obtained by electron energy loss spectroscopy [ 20,2 11, so the 200300 nm region in the gas-phase spectrum is accurately described by a strong peak at x 250 nm. This in turn is coherent with the astrophysical characteristics of RCorBor stars, which exhibit a single spectral peak at z 240 nm in this region [ 91. The results obtained in this work also suggest that Renge’s conclusions for O-O components can also be applied to the other spectral peaks, which is quite interesting taking into account that the different excited electronic states of a molecular system are pola&able to a variable extent. Acknowledgement We are greatly indebted to CICYT of Spain for tinancial support Project No. PB90-0226X02-0 1.
161
References
[I] H.W. Kroto, J.R. Health, S.C. O’Brien, R.F. Curl and R.E. Smalley, Nature 318 (1985) 162. [2] W. Kriitschmer, L.D. Lamb, K Fostiropoulos and D.R. Huffman, Nature 347 (1990) 354. [ 31J.P. Hare and H.W. Kroto, Accounts Chem. Res. 25 ( 1992) 106. [4]G.H. Herbig, Astrophys. J. 196 (1975) 129; 331 (1988) 999. (51 P.J. Sarre,Nature 353 (1991) 356. [6] S.J. Fossey, Nature 353 (1991) 393. [7] B.D. Savage and J.S. Mathis, Ann. Rev. Astrophys. 17 (1179) 73. [ 81 T.P. Stecher and B. DOM, Astrophys. J. 142 (1965) 1683. [9] E.L. Fitzpatrick and D. Massa, Astrophys, J. 307 (1986) 286. [lO]C.K. Mathews, M.S. Baba, T.S. Laksmi Narasimhan, R. Balasubramanian, N. Sivaraman, T.G. Srinivasan and P.R. Vasudeva Rao, J. Phys. Chem. 96 (1992) 3566. [ 111H. Ajie, M.M. Alvarez, S.J. Anz, R.D. Beck, F. Diederich, K. Fostiropoulos, Huffman, W. Krastcher, Y. Rubin, K-E. Schriever, D. Sensharma and R.L. Wbetten, J. Phys. Chem. 94 (1990) 8630. [ 121 J.P. Hare, H.W. Kroto and R. Taylor, Chem. Phys. Letters 177 (1991) 394. [ 131P.M. Allemand, A. Koch, F. Wudl, Y. Rubin, F. Diederich, M.M. Alvarez, S.J. Anz and R.L. Whetten, J. Am. Chem. sot. 113 (1991) 1050. [ 14 ] S. Leach, M. Vervloet, A. Desprt%, E. Bmheret, J.P. Hare, T.J. Dennis, H.W. Kroto, R. Taylorand R.M. Walton, Chem. Phys. 160 (1992) 451. [ 151 J. Catalan and J. Elguero, J. Am. Chem. Sot. 115 (1993) 9249. [ 161 R.L. Whetten, M.M. Alvarez, S.J. Anz, K-E. Schriver, R.D. Beck, F. Diederich, Y. Rubin, R. Et& C.S. Foote, A.P. Darmanyan and J.W. Arbogast, Mater. Res. Sot. Symp. Proc.206 (1991)3. [ 171R.E. Haufler, Y. Chai, L.P.F. Chibante, M.R. Fraelich,R.B. Weisman, R.F. Curl and R.S. Smalley, J. Chem. Phys. 95 (1991) 2197. [ 181 Z. Gasyna, P.N. Schatz, J.P. Hare, T.J. Dennis, H.W. Kroto, R. Taylor and R.M. Walton, Chem. Phys. Letters 183 ( 1991) 283. [ 19 ] I. Renge, J. Photochem. Photobiol. A 69 ( 1992) 135. [ 201 C. Bulhard, M. Allan and S. Leach, Chem. Phys. Letters 209 (1993) 434. [ 211R. Abouaf, J. Pommier and S. Cveejanovich, Chem. Phys. Letters 213 (1993) 503.
ELSEVIER
CHEMICAL
Chemical Physics Letters 223 (1994) 159-161
Towards the gas-phase UV-VIS absorption spectrum of &-, J. CatalAn Departamentode QuimicaFisica Aplicada,UniversidadAutbnomade Madrid, CantoBlanco, 28049 Madrid, Spain Received 2 1 March 1994
By analyzing the UV-VIS spectra for Cm in a series of n-alkanes, the positions of the absorption peaks in the corresponding gas-phase Cso spectrum were estimated from linear relations between the former positions and the corresponding Lorenz-Lorenz functions for the solvents.
1. Introduction Ever since large carbon clusters were found to be highly stable in 1985 [ I], much work has been devoted to investigating the electronic states of buckminsterfidlerene (CL&, promoted by the recent availability of macroscopic amounts [ 21 and the interest in checking for its presence in interstellar space. Recently, Hare and Kroto [ 3 ] suggested that certain signals detected in the so-called ‘diffuse interstellar bands’ [ 4-61 and the unidentified 2 17 nm band [ 79] might belong to CsO. Checking this hypothesis would be much easier were the gas-phase UV-VIS spectrum of C& available; however, this is not the case because the amount of required for the spectrum to be recorded could only be obtained by substantially raising the working temperature #l. On the other hand, several UV-VIS spectra for Cao in various solvents have indeed been recorded including those in dilute n-hexane [ 1I-141, cyclohexane [ 15 ] and methylcyclohexane [ 16 ] at room tem-
*’ When temperature reaches 700 K, C, vapour pressure in the equilibriumwiththepuresolidisonly4.12x1O-3Pa[1O],which is equivalent to a concentration in the gas phase of practically 7x lo-‘OM.
perature; those in methylcyclohexane [ 161, 3methylpentane and mixtures of the two [ 16,171 at 77IQthatinanargonmatrixat4K [18];andthe 375-415 and 595-635 nm regions for a sample that was supersonically cooled by using the resonant twophoton ionization (R2PI) technique [ 17 1. Recently, Renge showed [ 191 the possibility of precisely determining the position of the O-O component of a chromophore in the gas phase from the relation between such a position in a series of n-alkanes and the corresponding values for the LorenzLorenzfunction,f(n2)=(n2-l)/(n*+2),wheren is the refractive index. Based on this finding, in this work we approached the gas-phase UV-VIS spectrum of Cm by analysing its spectra in a series of nalkanes. The analysis was applied not only to the O-O component, but also to all those spectral peaks that can be detected precisely in order to subsequently predict the gas-phase spectrum for C6,,.
2. Experimental Spectra were recorded on a Cary 5 W-VIS spectrophotometer using a matched pair of cuvettes that were thermostated at 25°C. The C,, sample used was
0009-2614/94/$07.00 0 1994 Elsevier Science B.V. All rights reserved SSDZOOO9-2614(94)00448-Y
J. Catakin/Chemical PhysicsLetters223 (1994) 159-161
160
of the same purity as that employed in ref. [ 16 1. The n-alkanes used as solvents were all of spectroscopic grade and a high purity ( > 99%). CsOsolutions were made at a concentration of x 1 x 1O-’ M.
3. Results and discussion Table 1 lists the positions (in nm) of the 13 most representative peaks in the UV-VIS spectrum of C6,, in the different n-alkanes tested. The nomenclature
Table 1 Absorption spectra of C, in n-alkanes and in the gas phase: band wavelengths Band code ’
Band wavelength n-pentane
TO r2 A 73
t b A0 Al A3
C E G
619.4 591.2 589.4 567.8 540.6 427.4 421.8 407.8 403.8 390.6 328.3 256.2 210.0
’ Ref. [141. b See text.
(nm)
n-hexane
620.0 598.0 590.3 568.0 541.3 427.8 422.1 408.2 404.0 391.0 328.4 256.6 211.0
n-heptane
620.4 598.4 590.4 568.4 542.0 428.0 422.6 408.2 404.2 391.2 328.4 256.6 211.2
n-octane
620.4 598.4 591.0 568.6 542.4 428.0 422.6 408.4 404.4 391.2 328.6 256.8 212.0
n-nonane
621.0 598.8 590.6 568.6 542.8 428.2 422.8 408.6 404.4 391.4 328.8 257.2 213.0
n-dodecane
621.4 599.4 592.2 569.6 543.6 428.4 423.0 408.6 404.8 391.6 329.0 257.4 213.4
n-pentadecane
621.6 599.5 592.2 570.4 543.8 428.6 423.4 408.8 404.8 391.6 329.2 257.6 214.0
gas phase predicted b
exp. c
607.3 + 0.2 583.7f0.2 574.3+ 0.2 554.2kO.3 522.9fO.l 421.4fO.l 413.6fO.l 402.850.1 397.9fO.l 385.3kO.l 323.1 +O.l 248.750.1 190.0f0.2
607
402.4 398.0 385.7
“Ref. [17].
zoo
500
800
Wavelength
Fig. 1. Absorption spectrumof&,in (forbandcodeseeref. [14]).
n-heptane solution. (a) 200-800 nm. (b) 370-450nm;
(a)X20;
and (c) 415-8OOnm; (a)X 180
J. Catakin /Chemical Physicstitters 223 (1994) X5%161
used was originally proposed by Leach et al. [ 15 I. Fig. 1 shows the positions of the most readily identifiable peaks in the spectrum of CM in n-heptane, which are analysed below. As can be seen, there was good correlation between the positions of the spectral peaks (in cm-‘) and f( n2); the mean correlation coefficient was 0,976 and the predicted peak positions were subject to relatively small errors (less than 0.3 nm). It is interesting to note that the prediction for the O-O component (607.3 f0.2 nm) is quite consistent with the value obtained by Smalley and coworkers [ 18 ] for a supersonically cooled sample ( 607 nm), and so are the positions of peaks A,,, A, and Aj. In addition, because no substantial changes in the relative intensities of the peaks obtained for C&, in the different n-alkanes were observed, such intensities must be roughly similar in the gas-phase spectrum. Accordingly, our predictions must be faithful reproductions of the peaks in the gas-phase spectrum of Cm. The shifts in the high-end peaks from n-hexane to the gas phase are not constant, but vary between 330-470 cm-‘; others, such as peak 6i, are shifted by 650 cm-‘, and still others such as C, E and G are shifted much more markedly (by 500,120O and 5000 cm-‘, respectively). It is interesting to note that peak G is shifted so strongly that it is pushed into the vacuum UV region. This is consistent with the information obtained by electron energy loss spectroscopy [ 20,2 11, so the 200300 nm region in the gas-phase spectrum is accurately described by a strong peak at x 250 nm. This in turn is coherent with the astrophysical characteristics of RCorBor stars, which exhibit a single spectral peak at z 240 nm in this region [ 91. The results obtained in this work also suggest that Renge’s conclusions for O-O components can also be applied to the other spectral peaks, which is quite interesting taking into account that the different excited electronic states of a molecular system are pola&able to a variable extent. Acknowledgement We are greatly indebted to CICYT of Spain for tinancial support Project No. PB90-0226X02-0 1.
161
References
[I] H.W. Kroto, J.R. Health, S.C. O’Brien, R.F. Curl and R.E. Smalley, Nature 318 (1985) 162. [2] W. Kriitschmer, L.D. Lamb, K Fostiropoulos and D.R. Huffman, Nature 347 (1990) 354. [ 31J.P. Hare and H.W. Kroto, Accounts Chem. Res. 25 ( 1992) 106. [4]G.H. Herbig, Astrophys. J. 196 (1975) 129; 331 (1988) 999. (51 P.J. Sarre,Nature 353 (1991) 356. [6] S.J. Fossey, Nature 353 (1991) 393. [7] B.D. Savage and J.S. Mathis, Ann. Rev. Astrophys. 17 (1179) 73. [ 81 T.P. Stecher and B. DOM, Astrophys. J. 142 (1965) 1683. [9] E.L. Fitzpatrick and D. Massa, Astrophys, J. 307 (1986) 286. [lO]C.K. Mathews, M.S. Baba, T.S. Laksmi Narasimhan, R. Balasubramanian, N. Sivaraman, T.G. Srinivasan and P.R. Vasudeva Rao, J. Phys. Chem. 96 (1992) 3566. [ 111H. Ajie, M.M. Alvarez, S.J. Anz, R.D. Beck, F. Diederich, K. Fostiropoulos, Huffman, W. Krastcher, Y. Rubin, K-E. Schriever, D. Sensharma and R.L. Wbetten, J. Phys. Chem. 94 (1990) 8630. [ 121 J.P. Hare, H.W. Kroto and R. Taylor, Chem. Phys. Letters 177 (1991) 394. [ 131P.M. Allemand, A. Koch, F. Wudl, Y. Rubin, F. Diederich, M.M. Alvarez, S.J. Anz and R.L. Whetten, J. Am. Chem. sot. 113 (1991) 1050. [ 14 ] S. Leach, M. Vervloet, A. Desprt%, E. Bmheret, J.P. Hare, T.J. Dennis, H.W. Kroto, R. Taylorand R.M. Walton, Chem. Phys. 160 (1992) 451. [ 151 J. Catalan and J. Elguero, J. Am. Chem. Sot. 115 (1993) 9249. [ 161 R.L. Whetten, M.M. Alvarez, S.J. Anz, K-E. Schriver, R.D. Beck, F. Diederich, Y. Rubin, R. Et& C.S. Foote, A.P. Darmanyan and J.W. Arbogast, Mater. Res. Sot. Symp. Proc.206 (1991)3. [ 171R.E. Haufler, Y. Chai, L.P.F. Chibante, M.R. Fraelich,R.B. Weisman, R.F. Curl and R.S. Smalley, J. Chem. Phys. 95 (1991) 2197. [ 181 Z. Gasyna, P.N. Schatz, J.P. Hare, T.J. Dennis, H.W. Kroto, R. Taylor and R.M. Walton, Chem. Phys. Letters 183 ( 1991) 283. [ 19 ] I. Renge, J. Photochem. Photobiol. A 69 ( 1992) 135. [ 201 C. Bulhard, M. Allan and S. Leach, Chem. Phys. Letters 209 (1993) 434. [ 211R. Abouaf, J. Pommier and S. Cveejanovich, Chem. Phys. Letters 213 (1993) 503.