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Effect of hydrogen bonding on the vibrational dephasing time in glycerol
8 October 1982
CHEMICAL PHYSICS LETTERS
Volums 91. number 1
EFFECT OF HYDROCEN BONDING ON THE VIBRATIONAL DEPHASINCTITME lN GLYCEROL
R. DOFWNVILLE, WM. FRANKLIN, N. OCKhlAN and R.R. ALFANO Ulrrafust Spectroscopy and Law Laboratory, Physics Deprrrtment, The Ctty College ofXew York, New York, New York 10031, VS.4
The nbratlonal dephasmg of the methyl CH2 symmclnc stretch made III glycerol was duectly measured over cd tcmpersture range usmg plmsecond cohercnr Raman pump and probe spectroscopy. The dephlsing time was mcrcasc dramatically a~ the tcmpcralure oi the supercooled hqmd ws lowered. T~s observation s altnbuted lo cd hydrogen bondrng with dccrcssmg temperature whch hmders the dephasmg of the CHz vibration by reducmg
an extendfound to the u~creasmolecular
The knowledge of the vrbratlonal and rotational motions of molecules in the condensed state is indispensable for a full understanding of the dynamics and mteractrons in the microscopic world of matter [ 11. A variety of experimental techniques has been employed to probe the dynarmcs of molecular motions. Recently, picosecond laser spectroscopy [2,3], has become available for directly measunng the kinetics of the vlbrational [3,4] and rotational [5] motion of molecules m the condensed state. Much picosecond work on vrbrational dephastng in the hquid state has been ploneered by Laubereau and Kaiser [4] _Direct measurement of the dephasing trme of vibratrons is achieved by fist esciting the vibratron of molecules by an intense picosecond laser pulse via stimulated Raman [6] or parametric beating [3,4]. A weak probe pulse properly delayed wrth respect to the pump pulse can directly morutor the dephasing and population of the excited vibrations as function of time [3,4]. There have been several theoretical models proposed to account for dephasmg [7-l I]_ The mechanisms arise from a vmety ofmteractronssuch as: resonant energy transfer [ 121, collisions [7], hydrodynamic proc~ses
In this letter, we present experimental data on the fist direct measurement on the vibrational dephasing of a strongly associated liquid, glycerol, over an extended temperature range. Experimental evidence is presented that correlates the dephasing interaction in this strongly associated liquid m its supercooled state wnh the strength of I@roge,r bonding. Our experimental arrangement is sirmlar to that of Laubereau and Kaiser [4]. A mode-locked Nd : glass oscillator with single pulse selector is amplified, passed through a KLP crystal producing a 4 ps pulse at 530 MI. This pulse is then divided into a pump and a probe polarized perpendicularly to each other. The pulses traveled colhnearly through a 10 cm sample located in a dewar. A two dimensional OhlA coupled to a spectrograph was used to measure the probe Stokes signals at different delay times. The dephasing times of the 2886 cm-t CHZ vibration as a function of temperature from 300 to 200 K were determined from the decay of the coherent Stokes probe signal as a function of delay time between the pump and probe laser pulses. As shown in fig. 1, the vibrational dephasing time increases as the temper.
[S] , couplu~p of h@-
modes [9],
ature
and attrac-
value
bath
interactions,
and low-frequency
fast and slow repulsive
tive mteractions.[ lo,1 I], and population changes, to name a few. The dephasing times predicted by these theones [7-i l] were found KI accord vnth the experimental results of several simple non-associated, polyatomic hquids.
100
decreases.
An e~perime~~~I
data point
is the mean
of at least 15 laser shots. In fs_ 2, the depha&g times extracted 5-m temporal profiles are plotted versus the inverse of the temperature. The data are fitted to the equation: w 0 009-2614/82/0000-0000/$02.75
0 1982 North-Holland
CHEMICAL
Volume 91. number I
PHYSICS LETTERS
8
Octabcr1982
whereTY is the dephasingtime,E,c is the activation energy,F is the temperature,and k ISthe Boltzmann constant. The upper sohd hne in fig. 2 represents the tit to eq. (1) yielding an energy E 75 +O.8 kcaI/mol and T (0)=80A~.=800 _
Flg.1.
Probe Stokes protiles 3s fun&on of d&y
etbnol;
(B) glycerol (17°C);
(C)glycerol
tune for (A)
(-55°C).
30 -20 --
IO --
I%. 2 Dephasmg time VCISUSthe uwcrse tcmpcrsture (0) and
cm-1 = The glycerol molecule’ [C3 Hs(OH)3 1 has three hydroxyl groups per molecule which can hydrogen bond with other glycerol molecules to form a polymerrc aggregate network which causes the high viscosity of this liquid. In fg_ 2. the reciprocal of the drfiusion coefficient,D-t, as a function of temperature is plotted from the data of Larsson and Dahlborg [ 131. The D values were extracted from neutron scattering experiments and were interpreted to arise from the motion of the CHzOH groups inhtbtted by hydrogen bonding [ 131. The salient feature of these curves is that the slopes of T, and D-1 are parallel. The activation energy [ 13) from the D-l curve is 3 + 1 kcal/mol. This is the energy needed to break a smgle hydrogen bond. The actrvation energy obtained from T, versus T-’ in fig. 2 is in excellent agreement wtth this value. This mchcates that the dephasmg time, T2, is inversely proportional to this diffusion coefficient. The infinite temperature dephasmg tune T.,(O) = 80 fs gives a measure of the correlation time of fluctuatron without local restrictions. Various dephasing trme models have been introduced to account for the dephasing of the molecular vibrations [7- I2 j . The colhsional [7] and hydrodynamtc [8] theories predict a decrease in the time wtth a decrease IIItemperature - which is opposite to our observation. The exchange models [9.12] cannot account for the 800 cm-t excitation energy. The slow modulation models [ IO.11J are concerned with the inhomogeneous lurewidths and predict the linewrdths to increase with decreasing temperature. The dephasing time measurements obtained from coherent Stokes scattering are a direct measure of the homogeneous linewidths [4,l4] _These models have been developed for low.viscostly non-associated liqutds. A theoretical treatment applied to high-viscosrty associated liqurds remains to be formulated. The dephzrsingof CH, is most hkely due to the participation of rotational, rocking, torsions. stcric, and other low-frequency modes [9]. Our results strongly suggest that these dephasing interacttons of the CH stretch vrbratronalmode are significantly reduced by
inverse of the difiuslon cocfficlcnt YCISUSthe mvcrsc tcmpcrJturc
1131w. tcli
Volume 92. number 1
CHEMICAL PHYSICS LETTERS
8 October
1982
hydrogen bonding [l] which inhibits and restricts these motions [9] _Our conclusions are further ~pported by the Raman measurements by Wang and Wright [lS] showmg rhat the Iow.fre~uency modes are inhibited by hydrogen bonding. Upon cooling the sample, the hydrogen bond breakage diminishes causing the formation of large aggregates which slow down local molecular motions and environmental fluctuations. This resulr accounts for our observed large increase in the vtbrat~onai depha~~ time with de~r~a~~temperarure.
131 R R. Alfano and S L. Shapno, Sci. Am. 228 (1973) 42: Phys Rev. Letters 26 (1971) 1247; R.R A&no. Bull. Am. Phys. Sot. 15 (1970) 1324. 141 A. Laubereau and W. Raer. Rev. Mod. Phys. 50 (1978) 607; D von der Lmde. in: Ultrashort light pulses, ed. S.L Shapuo (Sprmger, BerIm, 1977). 151 P.P. Ho and R.R Al&o. J. Chcm. Phys 67 (1977) 1004; 68(1978)4551;74(1981) 1805. 161 N. BloembeEen, Am. J Phys 35 (1967) 989; R.L. Carmen, F. Shimuu. C S. Wang and N. Bioembergen,
We thank Dr. R. Lauver for contmued interest in the research and NASA for support of research under grant NAG 3-130.
(1975) 6. IS] D.W. Oxtoby, J. Chem. Phys 70 (1979) 2605 191 S Marks, PA. Cornellus and C. Hams, I. Chem. Phys. 73
[ 11 S.
BrltOS
and Rhl.
of molcculx
PICA.
cds., Vlbratronai spt?ctroscopy
hqulds and sobds. NATO Series B Physxs,
Vol. 56 (Plenum Press. New York, 1980) [a] A 3 Dehlariz, D.A Sterner and W H. Glen, (1972) 3782
102
Scrence 156
Phys.Rex At f1970) 60; J.& Chordmaw zmd W. K&et. Phys. Rev. 144 (1966)676. (71 S F. FEher and A Lauberrau, Chem. Phys. Letters 35
(1980) 3069. IlO] W. Rorhschdd, J. Chem. Phys. 65 (1976) 455;2958. [ 1 l] R S. Schwetler and D. Chandler, J. Chem Phys. 76 (1982) 2296. iI21 R. Abbott and D W. Ouroby, J. Chem. Phys. 70 (1979) [131 K E. Larsson and 0. Dahlborg, Physica 30 (1964) 1561. I141 _ SM. George. H. Auwerer and C B. Hti, J Chem. Phys 73 (1980)%573. [ 151 C.H. Wang and R.3. W~gb~,J.~em. Phys.SS (1971) 3300.
CHEMICAL PHYSICS LETTERS
Volums 91. number 1
EFFECT OF HYDROCEN BONDING ON THE VIBRATIONAL DEPHASINCTITME lN GLYCEROL
R. DOFWNVILLE, WM. FRANKLIN, N. OCKhlAN and R.R. ALFANO Ulrrafust Spectroscopy and Law Laboratory, Physics Deprrrtment, The Ctty College ofXew York, New York, New York 10031, VS.4
The nbratlonal dephasmg of the methyl CH2 symmclnc stretch made III glycerol was duectly measured over cd tcmpersture range usmg plmsecond cohercnr Raman pump and probe spectroscopy. The dephlsing time was mcrcasc dramatically a~ the tcmpcralure oi the supercooled hqmd ws lowered. T~s observation s altnbuted lo cd hydrogen bondrng with dccrcssmg temperature whch hmders the dephasmg of the CHz vibration by reducmg
an extendfound to the u~creasmolecular
The knowledge of the vrbratlonal and rotational motions of molecules in the condensed state is indispensable for a full understanding of the dynamics and mteractrons in the microscopic world of matter [ 11. A variety of experimental techniques has been employed to probe the dynarmcs of molecular motions. Recently, picosecond laser spectroscopy [2,3], has become available for directly measunng the kinetics of the vlbrational [3,4] and rotational [5] motion of molecules m the condensed state. Much picosecond work on vrbrational dephastng in the hquid state has been ploneered by Laubereau and Kaiser [4] _Direct measurement of the dephasing trme of vibratrons is achieved by fist esciting the vibratron of molecules by an intense picosecond laser pulse via stimulated Raman [6] or parametric beating [3,4]. A weak probe pulse properly delayed wrth respect to the pump pulse can directly morutor the dephasing and population of the excited vibrations as function of time [3,4]. There have been several theoretical models proposed to account for dephasmg [7-l I]_ The mechanisms arise from a vmety ofmteractronssuch as: resonant energy transfer [ 121, collisions [7], hydrodynamic proc~ses
In this letter, we present experimental data on the fist direct measurement on the vibrational dephasing of a strongly associated liquid, glycerol, over an extended temperature range. Experimental evidence is presented that correlates the dephasing interaction in this strongly associated liquid m its supercooled state wnh the strength of I@roge,r bonding. Our experimental arrangement is sirmlar to that of Laubereau and Kaiser [4]. A mode-locked Nd : glass oscillator with single pulse selector is amplified, passed through a KLP crystal producing a 4 ps pulse at 530 MI. This pulse is then divided into a pump and a probe polarized perpendicularly to each other. The pulses traveled colhnearly through a 10 cm sample located in a dewar. A two dimensional OhlA coupled to a spectrograph was used to measure the probe Stokes signals at different delay times. The dephasing times of the 2886 cm-t CHZ vibration as a function of temperature from 300 to 200 K were determined from the decay of the coherent Stokes probe signal as a function of delay time between the pump and probe laser pulses. As shown in fig. 1, the vibrational dephasing time increases as the temper.
[S] , couplu~p of h@-
modes [9],
ature
and attrac-
value
bath
interactions,
and low-frequency
fast and slow repulsive
tive mteractions.[ lo,1 I], and population changes, to name a few. The dephasing times predicted by these theones [7-i l] were found KI accord vnth the experimental results of several simple non-associated, polyatomic hquids.
100
decreases.
An e~perime~~~I
data point
is the mean
of at least 15 laser shots. In fs_ 2, the depha&g times extracted 5-m temporal profiles are plotted versus the inverse of the temperature. The data are fitted to the equation: w 0 009-2614/82/0000-0000/$02.75
0 1982 North-Holland
CHEMICAL
Volume 91. number I
PHYSICS LETTERS
8
Octabcr1982
whereTY is the dephasingtime,E,c is the activation energy,F is the temperature,and k ISthe Boltzmann constant. The upper sohd hne in fig. 2 represents the tit to eq. (1) yielding an energy E 75 +O.8 kcaI/mol and T (0)=80A~.=800 _
Flg.1.
Probe Stokes protiles 3s fun&on of d&y
etbnol;
(B) glycerol (17°C);
(C)glycerol
tune for (A)
(-55°C).
30 -20 --
IO --
I%. 2 Dephasmg time VCISUSthe uwcrse tcmpcrsture (0) and
cm-1 = The glycerol molecule’ [C3 Hs(OH)3 1 has three hydroxyl groups per molecule which can hydrogen bond with other glycerol molecules to form a polymerrc aggregate network which causes the high viscosity of this liquid. In fg_ 2. the reciprocal of the drfiusion coefficient,D-t, as a function of temperature is plotted from the data of Larsson and Dahlborg [ 131. The D values were extracted from neutron scattering experiments and were interpreted to arise from the motion of the CHzOH groups inhtbtted by hydrogen bonding [ 131. The salient feature of these curves is that the slopes of T, and D-1 are parallel. The activation energy [ 13) from the D-l curve is 3 + 1 kcal/mol. This is the energy needed to break a smgle hydrogen bond. The actrvation energy obtained from T, versus T-’ in fig. 2 is in excellent agreement wtth this value. This mchcates that the dephasmg time, T2, is inversely proportional to this diffusion coefficient. The infinite temperature dephasmg tune T.,(O) = 80 fs gives a measure of the correlation time of fluctuatron without local restrictions. Various dephasing trme models have been introduced to account for the dephasing of the molecular vibrations [7- I2 j . The colhsional [7] and hydrodynamtc [8] theories predict a decrease in the time wtth a decrease IIItemperature - which is opposite to our observation. The exchange models [9.12] cannot account for the 800 cm-t excitation energy. The slow modulation models [ IO.11J are concerned with the inhomogeneous lurewidths and predict the linewrdths to increase with decreasing temperature. The dephasing time measurements obtained from coherent Stokes scattering are a direct measure of the homogeneous linewidths [4,l4] _These models have been developed for low.viscostly non-associated liqutds. A theoretical treatment applied to high-viscosrty associated liqurds remains to be formulated. The dephzrsingof CH, is most hkely due to the participation of rotational, rocking, torsions. stcric, and other low-frequency modes [9]. Our results strongly suggest that these dephasing interacttons of the CH stretch vrbratronalmode are significantly reduced by
inverse of the difiuslon cocfficlcnt YCISUSthe mvcrsc tcmpcrJturc
1131w. tcli
Volume 92. number 1
CHEMICAL PHYSICS LETTERS
8 October
1982
hydrogen bonding [l] which inhibits and restricts these motions [9] _Our conclusions are further ~pported by the Raman measurements by Wang and Wright [lS] showmg rhat the Iow.fre~uency modes are inhibited by hydrogen bonding. Upon cooling the sample, the hydrogen bond breakage diminishes causing the formation of large aggregates which slow down local molecular motions and environmental fluctuations. This resulr accounts for our observed large increase in the vtbrat~onai depha~~ time with de~r~a~~temperarure.
131 R R. Alfano and S L. Shapno, Sci. Am. 228 (1973) 42: Phys Rev. Letters 26 (1971) 1247; R.R A&no. Bull. Am. Phys. Sot. 15 (1970) 1324. 141 A. Laubereau and W. Raer. Rev. Mod. Phys. 50 (1978) 607; D von der Lmde. in: Ultrashort light pulses, ed. S.L Shapuo (Sprmger, BerIm, 1977). 151 P.P. Ho and R.R Al&o. J. Chcm. Phys 67 (1977) 1004; 68(1978)4551;74(1981) 1805. 161 N. BloembeEen, Am. J Phys 35 (1967) 989; R.L. Carmen, F. Shimuu. C S. Wang and N. Bioembergen,
We thank Dr. R. Lauver for contmued interest in the research and NASA for support of research under grant NAG 3-130.
(1975) 6. IS] D.W. Oxtoby, J. Chem. Phys 70 (1979) 2605 191 S Marks, PA. Cornellus and C. Hams, I. Chem. Phys. 73
[ 11 S.
BrltOS
and Rhl.
of molcculx
PICA.
cds., Vlbratronai spt?ctroscopy
hqulds and sobds. NATO Series B Physxs,
Vol. 56 (Plenum Press. New York, 1980) [a] A 3 Dehlariz, D.A Sterner and W H. Glen, (1972) 3782
102
Scrence 156
Phys.Rex At f1970) 60; J.& Chordmaw zmd W. K&et. Phys. Rev. 144 (1966)676. (71 S F. FEher and A Lauberrau, Chem. Phys. Letters 35
(1980) 3069. IlO] W. Rorhschdd, J. Chem. Phys. 65 (1976) 455;2958. [ 1 l] R S. Schwetler and D. Chandler, J. Chem Phys. 76 (1982) 2296. iI21 R. Abbott and D W. Ouroby, J. Chem. Phys. 70 (1979) [131 K E. Larsson and 0. Dahlborg, Physica 30 (1964) 1561. I141 _ SM. George. H. Auwerer and C B. Hti, J Chem. Phys 73 (1980)%573. [ 151 C.H. Wang and R.3. W~gb~,J.~em. Phys.SS (1971) 3300.