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Picosecond 266 nm photolysis of neat liquids: Solvated electron formation in water and alcohols
Volume 98. number 3
CHEMICAL
PHYSICS LETTERS
24 June 1983
PICOSECOND266 nm PHOTOLYSIS OF NEAT LIQUIDS: SOLVATED ELECTRON FORMATION IN WATER AND ALCOHOLS Hiroshi MIYASAKA, Hiroshi MASUHARA and Noboru MATAGA Department of Chemistry. Faculty of Engineering Science. Osaka Uniwrsitv. Toyonaka. OsaAz 560, Japn Received I4 hlarch 1983: in final form 8 April 1983
The picosecond time-resolved absorption spectra of water and some alcohols were measured by means of 266 nm multiphoton photolysis. The formation time of the solvated electron was estimated and compared with the results obtained by pulse radiolysis and laser photoionization of solute molecules.
1. introduction Measurement of transient absorption spectra by using a picosecond laser has been one of the most familiar and useful methods to study photophysical and photochemical primary processes_ Its short pulse duration, however, inevitably requires a high output power for measurement of picosecond transient absorption spectra, which often induces non-linear phenomena such as multiphoton excitation as well as multiphoton ionization and decomposition of molecules_ Actually, we have measured the excited-state absorption spectra of some neat liquids of unsaturated and/or aromatic compounds by means of laser photolysis with the third harmonic (355 MI) of a mode-locked Nd3+ : YAG laser [l] . Similar results were also obtained by using the second harmonic (347 nm) of a mode-locked ruby laser as the excitation pulse [2] _ When solvent molecules are excited by such a multiphoton process, the excitation is ultimately transferred from the solvent to solute molecules [3] _In the case of multiphoton ionization of the solvent, the circumstances may be similar to the case of excitation transfer_ Namely, the charge produced in the solvent may be transferred to solute molecules. These phenomena are very similar to primary processes in solution radiation chemistry, which are being studied by means of picosecond pulse radiolysis. In the present work, the picosecond fourth har0 009-2614/83/0000-0000/S
03.00 0 1983 North-Holland
manic pulse (266 MI) ofa Nd3+ I YAG laser hasbeen applied to neat H20, DzO, and some alcohols. Although these liquids are transparent at this wavelength, solvated electrons are formed at an early stage after excitation_ Their dynamics are compared with the results obtained by pulse radiolysis of these liquids and picosecond laser photolysis studies on the ionization of solute molecules in these solvents_
2. Experimental
A microcomputer-controlled picosecond laser photolysis system with a repetitive Nd3* : YAG laser was used to measure transient absorption spectra_ The details of this system have been reported elsewhere [4,5] _ The samples were excited with a single 266 run pulse with ~20 ps fwhm and OS-O.7 mJ output power. This excitation pulse was focused onto a spot of 0.2-0.3 cm diameter using a quartz lens with a focal length of 10 cm. The center of this spot was monitored by a picosecond continuum with a pulse width of 24 ps, which was generated by focusing the fundamental pulse (1064 nm) onto a quartz cell of 10 cm path length containing D20 (Uvasol99.95%). A double-beam optical arrangement was adopted, and it was possible to cover the spectral range of 380 nm in one shot by using a multichannel photodiode array (5 12 channel) (MCPD). The origin of the time axis in our measurements was deter277
Volume 9s. number 3
CfiCJlICAL
mined 3s follows.
The peak absorbance at 16s the S,, + S, absorption spectrum ofpyrene in heuane \\ds plotted against optical delay. The when the absorbance was a half of the plateau
PHYSICS LETTERS
nm of cyclotime value
u as defined as the origin of the time axis. Deionized Hz0 ~3s distilled once and redistilled with a distillation apparatus of a non-boiling type. D,O (Uv~sol 99.95%). methanol, ethanol, 2-propanol (dotne spectroscol). .nld ethylene glycol (Nakarai SpcciJ Guarantee) were used without futher purification. A!1 the sampleswere deaersted bj N, bubbling .uld measured in a Suprasil cell with 1 cm path length. Xieasurcnicrits were performed at 3 1 f 1OC.
3. Results
and discussion
Exitstion of H,O. D,O. methanol. ethanol. 3propanol .wd eth~ lene &co1 with a picosecond 266 nm 1x11s~ gives transient absorption spectra JS shown in fig. 1. All the spectra 3re very broad rind structure-
less. The peA positions 3x 7 15 ml for Hz0 and DZO. 645 nm for methanol. 730 nm for ethanol.and 590 11111 for cth? lene glycol. These spectra show no decay up to 3 11s.indickng rhdt the lifetimes of the transients 3re longer t1l.m 10 ns. Then spectra do not seem to be dscribdble to the excited singlet state. becsusc their lifetimes xe much longer than the fluorescence lifetimes (=I 11s)of,~lkmcs [6] and introduction of a OH group in alk~nes seems to enhance the degradation of the cxcitcd states. Actually. nu lluorescence data for
f.00
5m
6m
700 h,nm~~
500
600
Hz0 and these alcohols
have been reported. An alrernative assignment to the triplet states can also be excluded, because these transients are produced immediately after excitation in the picosecond time range,
and decomposition processes of H20, methanol and ethanol are the main deactivation channel of their escited states in the gas phase [7] _In conclusion, the present spectra are considered to be due to solvated
electrons because of their similarity to the well-known spectra of solvated electrons [S,9] _In the case of 2propanoi. no absorption peak was observed in the region between 400 and 760 rnn, but the spectrum is very similar to that est3blished for solvated electrons in this solvent [9] . This esplanation is consistent with a recent report that the multiphoton excitation of Hz0 with 193 and 248 nm laser pulses induces ionizstion in the gas phase [lo] _Moreover, formation of hydrsted electrons by 266 nm two-photon excitation has also been reported recently by IGkogosyan et al. [ 1 l] by messurement of the laser-induced photocurrent. These liquids are almost tr3nspxent 3t 266 nm (absorbrtnce
7m 2. Ewitntion intensit, dependences of the transient absorbsnces for ethylene gl) co1 (0) and pyrene in cyclohexane (*I. The peak absorbance of neat eth) lene gl> co1 (590 nm) and the pyrene S, - Sr transition (468 nm) a112plotted. Fi- ~
spcLtra of neat liquids obt&ed at 100 p’A.tcr excif.!rlon. (.I) H20. (b) DzO. (c) methanol, (d) eth.mol, (cl rth\ Icnr glycol, .md (I) bpropanol.
Fip. 1. TrxGrnt
27s
Jbsorption
24 June 1983
Volume 98. number 3
CHEMICAL PHYSICS LETTERS
24June1983
was increased. This behavior is mainly due to an inner filter effect and/or bleaching of the ground-state py-
rene molecule_ The contributions of these effects to the S,, + S 1 absorbance in transient spectroscopy hasbeen evaluated quantitatively in the case of pyrene for 355 nm excitation [5] _At any rate, the dependence of the absorbance of solvated electrons on excitation intensity is clearly different from that of pyrene; its upward deviation indicates that the generation of solvated electrons is through two- or higher-photon processes_ This is also confirmed in the case of the other liquids. The time-resolved transient absorption spectra of H20 and ethylene glycol are given in fig. 3. The spectra immediately after excitation are different from those at later stages, which may be due to the wavelength-dependent distribution of the arrival time of the picosecond continuum at the sample position. According to our recent study [5,12], the shorter the wavelength of the picosecond continuum, the later it reaches the sample. The difference of the arrival time between 450 and 650 nm is found to be x10- 15 ps. This difference of the arrival time affects the spectral shape immediately after excitation_ Since shorterwavelength light monitors the sample later than longer-
wavelength light, the transient absorption spectrum around 0 ps is apparently stronger in the blue part than in the red parts. Because of this effect, a simple comparison between the spectrum immediately after excitation and that at later stages is not appropriate, and a quantitative simulation considering the temporal properties of the picosecond continuum is required
Fig. 3. Time-resolved absorption spectra of neat Hz0 (a) ethylene glycol (b) obtained with 266 nm excitation.
and
Fi:. 4. Rise curves of the transient absorbances for (a) H2 0, (b) methanol, (c) ethylene glycol, and cd) 2-propanoi. The orbm of the time alis is defied at 468 nm (see text).
[5] _ However, it could be concluded that the generation of solvated electrons in these liquids is very fast. being almost completed within the escitation pulse width, 20 ps. since the spectrum at 33 ps is identical with those at later stages and no evolution is observed after this delay time. in order to estimate the formation time of solvated electrons, its absorbance is plotted against delay time in fig_ 4. For H1O, methanol, and ethylene glycol, the peak of each spectrum is analyzed, while the absorbance at 750 nm is plotted in thes case of Z-propanok The rise time of the absorbance of hydrated electrons from 10% to 90% of the plateau value is 27 f 3 ps. Since the formation time of hydrated electrons is known to be very fast (less than 0.3 ps) [ 13], this value may be determined by the pulse width of the multiphotonic excitation and that of the monitoring continuum_ The risetimes in methanol. ethylene glycol and Zpropanol are obtained to be 3 1 i 5,30 i 3, and 57 rt 4 ps respectively. By using the value of 20 ps for the exciting pulse width and 24~s for the monitoring pulse width, and assuming a simultaneous biphotonic process for ionization, we have simulated the rise curves of the solvated electron absorbance with its 279
CHEXllCAL
Volume 98. number 3 formation
time as parameter-The
results
24 June 1983
PHYSICS LETTERS
of this simu-
lation show that the formation time of the solvated electron is < 10 ps for methanol as well as ethylene gllycol. and 20-25 ps for 2-propanol. The formation process of solvated electrons has been investigated directly by means of picosecond pulse radlulysis and laser photoionization of the solute. The electron injected into solvent is first localized in a shallow trap. giving an absorption spectrum in the near infrared region [ 16 16]_ This localized electron then changes to a solvated electron with an absorption band in the visible region, ~vhich has been monitored for elucidating its formation time. The present form&ion time ofsolvated electrons in each liquid is in agreement with the results obtained by a pulse rrldiolysis study [ l-11. On the othe; hand. Wanget al. [ 171 reported the formation time ofsolvated electrons in methanol (17 f 3 ps) and ethanol (26 F 5 ps) by means of two-photon ionization of pyrene with the third harmonic of a mode-locked Nd’+ : glasslaser.Their values seem to be a little longer than ours and those obtained by pulse rxholysis. indicating that the salvation process depends on bow the electron is injected in the liquids. Namely. WI only the energy of the ionizing state but Aso its may determine the fate of the injected elecThe electron injected by electron pulse irradiation is solvated in the spurs where the disrriburions ofpositive ion and electron are quite different from rhat in J photochemic;ll system. Furthermore. rhe possibility oflocA heating due to inhomogencous energy dissipation along the trdck of the incident clecrron ma) influence the electron dynamics. Therefore. it seems to be rather difficult to determine rhc formation time of‘solvated electron under ideally homogeneous conditions. The present multiphoton excitJtIon may provide another method for elucidating electron sohation in nedt liquids.
The present multiphoton excitation of neat liquids is a new method to produce solvated electrons. In comparison with the other two methods of electron injection, the present method is considered hardly to pertrurb the homogeneous conditions of the neat liquid. A comparison of the results obtained by these three methods of electron injection may be fruitful for elucidating the picosecond dynamics of electrons in polar solvents. There is a possibility of solvent excitation in the laser photolysis in solution_ This process should be examined in detail in order to obtain reliable and accurate transient absorption spectra of solution systems. In the case of 3.55 nm photolysis, the present alcohols gave signals of stimulated Raman scattering and no information on solvated electrons was obtained, while nothing was induced in the case of water [l]_ Similar results were also obtained in the case of 532 nm photolysis. These photophysical behaviors of neat liquids depending on the excitation shortly.
wavelength will be published
Acknowledgement
chxxtel
tron 10 some extent.
NM and HM thank the Grant-in-Aid for Special Project Research on Photobiology from the Japanese Ministry of Education. Science, and Culture.
References
I I] H. Masuhnra, H. Miyasaka, N. lkeda and N. Mataga,Chem.
131
[41
4. Concluding
remarks
It is confirmed that 266 mn picosecond excitation and alcohols, which are transparent at this wavelength, leads to the formation of solvated e!ectrons. Multiphoton excitation is responsible for this process. and the formation time constants have been estimated.
of water
Phys. Letters 82 (1981) 59. Hidakd. T. Nakayama and H. Teranishi, Chem. Phys. Letters 82 (1981) 55. H. hliyauha, N. Ikeda. H. hiasuhara and N. hlataga, Abstract of the Symposium on Molecular Structure of Japan. Kyoro (1981); to be published. H. hfasuhara. N. Ikeda. H. Miyasaka and N. hlataga, J. Spectrosc. Sot. Japan 31 (1982) 19. H. Miyasaka. H. Masuhara and N. Mataga. Laser Chem., to be published_ W-R. Ware and R.L. Lyke. Chem. Phys. Letters 24 (1974) 195; L. Flamigni, F. Barigeiletti. S. Dellonte and G. Orlandi, Chem. Phyr Letters 89 (1982) 13. H. Okabe. Photochemistry of small molecules (Wiley-
[ 21 K. Hamanoue,T.
151 [61
171
Interscience, (1978)
280
New York, 1978) p_ 201.
[ 81 G-E. Hall and G.A. Kenney-Wallace, Chem. Phys. 32 313.
Volume
9s. number 3
[9] L.M. Dorfman and F.Y. Jou. Electrons in (Springer. Berlin. 1973) p_ 447. [ lo] R-J. Donovan, Specialist Periodical Report, and Enegy Transfer, VoL 4 (Chem. Sot., 1980) p. 126. [ 1 l] D.A. Angelov. D.A. Nikogosym and A.A.
CHEMICAL
PHYSICS LETTERS
fluids Gas Kinetics London,
Oraevsky.
Kvantovaya Electron. 7 (1980) 2573; D.N. Nikogosyan and D.A. Angelov, Chem. Phys. Letters 77 (1981) 208. [ 121 H. hlasuhara, H. hliyasaka, A. Karen,T. Uemiya, N. hfataga, hi. Koishi. -4. Takeshima and Y. Tsuchiya, Opt. Commun. 44 (1983) 426.
24 June 1983
[ 131 J. Wiesenfeld and E. Ippen, Chem. Phys. Letters 73 (1980) 47. [ 141 G-A. Kenney-\vallace and C-D. Jonah, J. Phys. Chem. 86 (1982) 2572. [ 151 D. Huppert, G.A. Kenney-Wallace and P.M. Rentzepis. J. Chem. Phyr 7.5 (1981) 2265.
[ 16) W-J. Chase and J-W_Hunt, J. Phys. Chem. 76 (1975) 2835. [ 171 Y. Wang. hl.H. Crawfold, M.J. hlcAuliffe and K.B. Eisenthal, Chem. Phys. Letters 74 (1980) 160.
281
CHEMICAL
PHYSICS LETTERS
24 June 1983
PICOSECOND266 nm PHOTOLYSIS OF NEAT LIQUIDS: SOLVATED ELECTRON FORMATION IN WATER AND ALCOHOLS Hiroshi MIYASAKA, Hiroshi MASUHARA and Noboru MATAGA Department of Chemistry. Faculty of Engineering Science. Osaka Uniwrsitv. Toyonaka. OsaAz 560, Japn Received I4 hlarch 1983: in final form 8 April 1983
The picosecond time-resolved absorption spectra of water and some alcohols were measured by means of 266 nm multiphoton photolysis. The formation time of the solvated electron was estimated and compared with the results obtained by pulse radiolysis and laser photoionization of solute molecules.
1. introduction Measurement of transient absorption spectra by using a picosecond laser has been one of the most familiar and useful methods to study photophysical and photochemical primary processes_ Its short pulse duration, however, inevitably requires a high output power for measurement of picosecond transient absorption spectra, which often induces non-linear phenomena such as multiphoton excitation as well as multiphoton ionization and decomposition of molecules_ Actually, we have measured the excited-state absorption spectra of some neat liquids of unsaturated and/or aromatic compounds by means of laser photolysis with the third harmonic (355 MI) of a mode-locked Nd3+ : YAG laser [l] . Similar results were also obtained by using the second harmonic (347 nm) of a mode-locked ruby laser as the excitation pulse [2] _ When solvent molecules are excited by such a multiphoton process, the excitation is ultimately transferred from the solvent to solute molecules [3] _In the case of multiphoton ionization of the solvent, the circumstances may be similar to the case of excitation transfer_ Namely, the charge produced in the solvent may be transferred to solute molecules. These phenomena are very similar to primary processes in solution radiation chemistry, which are being studied by means of picosecond pulse radiolysis. In the present work, the picosecond fourth har0 009-2614/83/0000-0000/S
03.00 0 1983 North-Holland
manic pulse (266 MI) ofa Nd3+ I YAG laser hasbeen applied to neat H20, DzO, and some alcohols. Although these liquids are transparent at this wavelength, solvated electrons are formed at an early stage after excitation_ Their dynamics are compared with the results obtained by pulse radiolysis of these liquids and picosecond laser photolysis studies on the ionization of solute molecules in these solvents_
2. Experimental
A microcomputer-controlled picosecond laser photolysis system with a repetitive Nd3* : YAG laser was used to measure transient absorption spectra_ The details of this system have been reported elsewhere [4,5] _ The samples were excited with a single 266 run pulse with ~20 ps fwhm and OS-O.7 mJ output power. This excitation pulse was focused onto a spot of 0.2-0.3 cm diameter using a quartz lens with a focal length of 10 cm. The center of this spot was monitored by a picosecond continuum with a pulse width of 24 ps, which was generated by focusing the fundamental pulse (1064 nm) onto a quartz cell of 10 cm path length containing D20 (Uvasol99.95%). A double-beam optical arrangement was adopted, and it was possible to cover the spectral range of 380 nm in one shot by using a multichannel photodiode array (5 12 channel) (MCPD). The origin of the time axis in our measurements was deter277
Volume 9s. number 3
CfiCJlICAL
mined 3s follows.
The peak absorbance at 16s the S,, + S, absorption spectrum ofpyrene in heuane \\ds plotted against optical delay. The when the absorbance was a half of the plateau
PHYSICS LETTERS
nm of cyclotime value
u as defined as the origin of the time axis. Deionized Hz0 ~3s distilled once and redistilled with a distillation apparatus of a non-boiling type. D,O (Uv~sol 99.95%). methanol, ethanol, 2-propanol (dotne spectroscol). .nld ethylene glycol (Nakarai SpcciJ Guarantee) were used without futher purification. A!1 the sampleswere deaersted bj N, bubbling .uld measured in a Suprasil cell with 1 cm path length. Xieasurcnicrits were performed at 3 1 f 1OC.
3. Results
and discussion
Exitstion of H,O. D,O. methanol. ethanol. 3propanol .wd eth~ lene &co1 with a picosecond 266 nm 1x11s~ gives transient absorption spectra JS shown in fig. 1. All the spectra 3re very broad rind structure-
less. The peA positions 3x 7 15 ml for Hz0 and DZO. 645 nm for methanol. 730 nm for ethanol.and 590 11111 for cth? lene glycol. These spectra show no decay up to 3 11s.indickng rhdt the lifetimes of the transients 3re longer t1l.m 10 ns. Then spectra do not seem to be dscribdble to the excited singlet state. becsusc their lifetimes xe much longer than the fluorescence lifetimes (=I 11s)of,~lkmcs [6] and introduction of a OH group in alk~nes seems to enhance the degradation of the cxcitcd states. Actually. nu lluorescence data for
f.00
5m
6m
700 h,nm~~
500
600
Hz0 and these alcohols
have been reported. An alrernative assignment to the triplet states can also be excluded, because these transients are produced immediately after excitation in the picosecond time range,
and decomposition processes of H20, methanol and ethanol are the main deactivation channel of their escited states in the gas phase [7] _In conclusion, the present spectra are considered to be due to solvated
electrons because of their similarity to the well-known spectra of solvated electrons [S,9] _In the case of 2propanoi. no absorption peak was observed in the region between 400 and 760 rnn, but the spectrum is very similar to that est3blished for solvated electrons in this solvent [9] . This esplanation is consistent with a recent report that the multiphoton excitation of Hz0 with 193 and 248 nm laser pulses induces ionizstion in the gas phase [lo] _Moreover, formation of hydrsted electrons by 266 nm two-photon excitation has also been reported recently by IGkogosyan et al. [ 1 l] by messurement of the laser-induced photocurrent. These liquids are almost tr3nspxent 3t 266 nm (absorbrtnce
7m 2. Ewitntion intensit, dependences of the transient absorbsnces for ethylene gl) co1 (0) and pyrene in cyclohexane (*I. The peak absorbance of neat eth) lene gl> co1 (590 nm) and the pyrene S, - Sr transition (468 nm) a112plotted. Fi- ~
spcLtra of neat liquids obt&ed at 100 p’A.tcr excif.!rlon. (.I) H20. (b) DzO. (c) methanol, (d) eth.mol, (cl rth\ Icnr glycol, .md (I) bpropanol.
Fip. 1. TrxGrnt
27s
Jbsorption
24 June 1983
Volume 98. number 3
CHEMICAL PHYSICS LETTERS
24June1983
was increased. This behavior is mainly due to an inner filter effect and/or bleaching of the ground-state py-
rene molecule_ The contributions of these effects to the S,, + S 1 absorbance in transient spectroscopy hasbeen evaluated quantitatively in the case of pyrene for 355 nm excitation [5] _At any rate, the dependence of the absorbance of solvated electrons on excitation intensity is clearly different from that of pyrene; its upward deviation indicates that the generation of solvated electrons is through two- or higher-photon processes_ This is also confirmed in the case of the other liquids. The time-resolved transient absorption spectra of H20 and ethylene glycol are given in fig. 3. The spectra immediately after excitation are different from those at later stages, which may be due to the wavelength-dependent distribution of the arrival time of the picosecond continuum at the sample position. According to our recent study [5,12], the shorter the wavelength of the picosecond continuum, the later it reaches the sample. The difference of the arrival time between 450 and 650 nm is found to be x10- 15 ps. This difference of the arrival time affects the spectral shape immediately after excitation_ Since shorterwavelength light monitors the sample later than longer-
wavelength light, the transient absorption spectrum around 0 ps is apparently stronger in the blue part than in the red parts. Because of this effect, a simple comparison between the spectrum immediately after excitation and that at later stages is not appropriate, and a quantitative simulation considering the temporal properties of the picosecond continuum is required
Fig. 3. Time-resolved absorption spectra of neat Hz0 (a) ethylene glycol (b) obtained with 266 nm excitation.
and
Fi:. 4. Rise curves of the transient absorbances for (a) H2 0, (b) methanol, (c) ethylene glycol, and cd) 2-propanoi. The orbm of the time alis is defied at 468 nm (see text).
[5] _ However, it could be concluded that the generation of solvated electrons in these liquids is very fast. being almost completed within the escitation pulse width, 20 ps. since the spectrum at 33 ps is identical with those at later stages and no evolution is observed after this delay time. in order to estimate the formation time of solvated electrons, its absorbance is plotted against delay time in fig_ 4. For H1O, methanol, and ethylene glycol, the peak of each spectrum is analyzed, while the absorbance at 750 nm is plotted in thes case of Z-propanok The rise time of the absorbance of hydrated electrons from 10% to 90% of the plateau value is 27 f 3 ps. Since the formation time of hydrated electrons is known to be very fast (less than 0.3 ps) [ 13], this value may be determined by the pulse width of the multiphotonic excitation and that of the monitoring continuum_ The risetimes in methanol. ethylene glycol and Zpropanol are obtained to be 3 1 i 5,30 i 3, and 57 rt 4 ps respectively. By using the value of 20 ps for the exciting pulse width and 24~s for the monitoring pulse width, and assuming a simultaneous biphotonic process for ionization, we have simulated the rise curves of the solvated electron absorbance with its 279
CHEXllCAL
Volume 98. number 3 formation
time as parameter-The
results
24 June 1983
PHYSICS LETTERS
of this simu-
lation show that the formation time of the solvated electron is < 10 ps for methanol as well as ethylene gllycol. and 20-25 ps for 2-propanol. The formation process of solvated electrons has been investigated directly by means of picosecond pulse radlulysis and laser photoionization of the solute. The electron injected into solvent is first localized in a shallow trap. giving an absorption spectrum in the near infrared region [ 16 16]_ This localized electron then changes to a solvated electron with an absorption band in the visible region, ~vhich has been monitored for elucidating its formation time. The present form&ion time ofsolvated electrons in each liquid is in agreement with the results obtained by a pulse rrldiolysis study [ l-11. On the othe; hand. Wanget al. [ 171 reported the formation time ofsolvated electrons in methanol (17 f 3 ps) and ethanol (26 F 5 ps) by means of two-photon ionization of pyrene with the third harmonic of a mode-locked Nd’+ : glasslaser.Their values seem to be a little longer than ours and those obtained by pulse rxholysis. indicating that the salvation process depends on bow the electron is injected in the liquids. Namely. WI only the energy of the ionizing state but Aso its may determine the fate of the injected elecThe electron injected by electron pulse irradiation is solvated in the spurs where the disrriburions ofpositive ion and electron are quite different from rhat in J photochemic;ll system. Furthermore. rhe possibility oflocA heating due to inhomogencous energy dissipation along the trdck of the incident clecrron ma) influence the electron dynamics. Therefore. it seems to be rather difficult to determine rhc formation time of‘solvated electron under ideally homogeneous conditions. The present multiphoton excitJtIon may provide another method for elucidating electron sohation in nedt liquids.
The present multiphoton excitation of neat liquids is a new method to produce solvated electrons. In comparison with the other two methods of electron injection, the present method is considered hardly to pertrurb the homogeneous conditions of the neat liquid. A comparison of the results obtained by these three methods of electron injection may be fruitful for elucidating the picosecond dynamics of electrons in polar solvents. There is a possibility of solvent excitation in the laser photolysis in solution_ This process should be examined in detail in order to obtain reliable and accurate transient absorption spectra of solution systems. In the case of 3.55 nm photolysis, the present alcohols gave signals of stimulated Raman scattering and no information on solvated electrons was obtained, while nothing was induced in the case of water [l]_ Similar results were also obtained in the case of 532 nm photolysis. These photophysical behaviors of neat liquids depending on the excitation shortly.
wavelength will be published
Acknowledgement
chxxtel
tron 10 some extent.
NM and HM thank the Grant-in-Aid for Special Project Research on Photobiology from the Japanese Ministry of Education. Science, and Culture.
References
I I] H. Masuhnra, H. Miyasaka, N. lkeda and N. Mataga,Chem.
131
[41
4. Concluding
remarks
It is confirmed that 266 mn picosecond excitation and alcohols, which are transparent at this wavelength, leads to the formation of solvated e!ectrons. Multiphoton excitation is responsible for this process. and the formation time constants have been estimated.
of water
Phys. Letters 82 (1981) 59. Hidakd. T. Nakayama and H. Teranishi, Chem. Phys. Letters 82 (1981) 55. H. hliyauha, N. Ikeda. H. hiasuhara and N. hlataga, Abstract of the Symposium on Molecular Structure of Japan. Kyoro (1981); to be published. H. hfasuhara. N. Ikeda. H. Miyasaka and N. hlataga, J. Spectrosc. Sot. Japan 31 (1982) 19. H. Miyasaka. H. Masuhara and N. Mataga. Laser Chem., to be published_ W-R. Ware and R.L. Lyke. Chem. Phys. Letters 24 (1974) 195; L. Flamigni, F. Barigeiletti. S. Dellonte and G. Orlandi, Chem. Phyr Letters 89 (1982) 13. H. Okabe. Photochemistry of small molecules (Wiley-
[ 21 K. Hamanoue,T.
151 [61
171
Interscience, (1978)
280
New York, 1978) p_ 201.
[ 81 G-E. Hall and G.A. Kenney-Wallace, Chem. Phys. 32 313.
Volume
9s. number 3
[9] L.M. Dorfman and F.Y. Jou. Electrons in (Springer. Berlin. 1973) p_ 447. [ lo] R-J. Donovan, Specialist Periodical Report, and Enegy Transfer, VoL 4 (Chem. Sot., 1980) p. 126. [ 1 l] D.A. Angelov. D.A. Nikogosym and A.A.
CHEMICAL
PHYSICS LETTERS
fluids Gas Kinetics London,
Oraevsky.
Kvantovaya Electron. 7 (1980) 2573; D.N. Nikogosyan and D.A. Angelov, Chem. Phys. Letters 77 (1981) 208. [ 121 H. hlasuhara, H. hliyasaka, A. Karen,T. Uemiya, N. hfataga, hi. Koishi. -4. Takeshima and Y. Tsuchiya, Opt. Commun. 44 (1983) 426.
24 June 1983
[ 131 J. Wiesenfeld and E. Ippen, Chem. Phys. Letters 73 (1980) 47. [ 141 G-A. Kenney-\vallace and C-D. Jonah, J. Phys. Chem. 86 (1982) 2572. [ 151 D. Huppert, G.A. Kenney-Wallace and P.M. Rentzepis. J. Chem. Phyr 7.5 (1981) 2265.
[ 16) W-J. Chase and J-W_Hunt, J. Phys. Chem. 76 (1975) 2835. [ 171 Y. Wang. hl.H. Crawfold, M.J. hlcAuliffe and K.B. Eisenthal, Chem. Phys. Letters 74 (1980) 160.
281