Intermolecular Vibrational Energy Exchange Directly Probed with
Ultrafast Two Dimensional Infrared Spectroscopy
Hongtao Bian, Wei Zhao, and Junrong Zheng
Supporting materials
200
180
Waiting time (ps)
160
140
120
100
80
60
40
20
2160
2170
2180
2190
2200
2210
2220
2230
2240
Probe Frequency (cm-1)
S1. Rotation-free pump/probe data of 1.8 wt% benzonitrile in CCl4 at room temperature.
One contour represents 4% of the intensity. The peak intensity ratio of the red/blue at
long delay times shows the cross section ratio between the combination band and the CN
0-1 transition. In the dilute solution, heat effect is negligible. In the mixed sample, the
heat effect is not negligible. The ratio determined here can be used to determine the ratio
of the contribution of L’ or L over that of heat to the red peaks in 2D IR spectra in panel
30ps in fig.1.
1
0.40
0.35
Absorbance
0.30
0.25
0.20
23
25
30
36
40
44
48
54
0.15
0.10
0.05
2210 2220 2230 2240 2250 2260 2270 2280
-1
Fequency (cm )
S2. Temperature dependent FTIR spectra of CD3CN and Benzonitrile mixture. The
temperature increase reduces the cross sections of both CN absorptions.
2
0.0
0.04
0.02
Data
Fit
-0.08 ±--0.45819
4.20218
-0.2
y0
A1
t1
-0.3
-0.4
±0.00576
±0.13165
-1
2209 cm
-0.5
Normalized Population
Normalized Population
-0.1
0.00
-0.02
Data: Data7_B
Model: ExpDec1
-0.04
Chi^2/DoF
= 0.00006
R^2
= 0.95225
-0.06
y0
A1
t1
0.00792
-0.09529
9.01705
±0.00111
±0.0023
±0.58767
-0.08
2245 cm-1 lifetime
-0.10
-0.6
0
50
100
150
200
0
50
Waiting Time (ps)
150
200
0.02
Normalized Population
0.3
Normalized Population
100
Waiting Time (ps)
0.2
Data: Data9_B
Model: ExpDec1
Chi^2/DoF
= 0.00015
R^2
= 0.99214
0.1
y0
A1
t1
-0.1504 ±0.00269
0.4
±0.00506
3.93288
±0.13499
0.0
2224 cm-1 grow rate
0.00
-1
2254 cm
Chi^2/DoF
= 0.00005
R^2
= 0.95311
-0.02
y0
A1
t1
-0.04
-0.07242
0.08321
7.62427
±0.00199
±0.00243
±0.66499
-0.06
-0.1
-0.08
-0.2
0
10
20
30
40
50
0
10
Waiting Time (ps)
20
30
40
50
Waiting Time (ps)
0.35
0.4
0.3
2263 cm
-1
Normalized Population
Normalized Population
0.30
2232 cm
Benzonitrile rotational relaxation
Chi^2/DoF
= 0.00028
R^2
= 0.98487
0.2
y0
A1
t1
0.1
-0.02474
0.40925
5.28495
±0.00224
±0.00588
±0.19584
0.0
-0.1
-1
0.25
CD3CN rotational relaxation
0.20
Chi^2/DoF
= 0.00041
R^2
= 0.95082
0.15
y0
A1
t1
0.0031 ±0.00239
0.34745
±0.0117
1.99421
±0.13241
0.10
0.05
0.00
-0.05
0
50
100
150
Waiting Time (ps)
200
0
50
100
150
200
Waiting Time (ps)
S3. Pump/probe data and fits to obtain the time constants
CN vibrational lifetimes are from single exponential fits to the pp signals at the CN 1-2
transition frequencies 2245 and 2209 cm-1, yielding TA  9 ps, TB  4.2 ps . The relaxation
time constants to L and L’ are obtained from fitting pp data at the combination band
absorption frequencies 2254 and 2224 cm-1 at delay shorter than 50ps,
yielding TAL  7.6 ps, TB  3.9 ps , since the combination band signal is from the excitation
of L or L’. The lifetimes of L and L’ are obtained from the decays of the pp data at the
combination band absorption frequencies 2254 and 2224 cm-1 at delay between 50 to
200ps. The energy ratio deposit into A and B and the transition dipole moment ratio are
determined from the IR absorption peak area ratio based on the Lambert Beer Law.
3
0.30
0.5
0.25
Benzonitrile in CCl4
CD3CN in CCl4
Absorbance
Absorbance
0.4
0.3
0.2
0.20
0.15
0.10
0.05
0.1
2180 2200 2220 2240 2260 2280 2300 2320
-1
Frequency (cm )
0.00
2190
2200
2210
2220
2230
2240
2250
-1
Frequency (cm )
S4. FTIR spectra of CD3CN and Benzonitrile in CCl4 showing the origins of small peaks
in pump/probe data and 2D IR data
4
200
180
Waiting time (ps)
160
140
120
100
80
60
40
20
2160
2170
2180
2190
2200
2210
2220
2230
2240
Probe Frequency (cm-1)
S5. Rotation-free pump/probe data of 2.5 wt% benzonitrile in chloroform at room
temperature. One contour represents 4% of the intensity.
5
Temperature Increase Estimation
The pump/probe signal difference between 20ps and 200ps delays experimentally
obtained is
T
T
T200 Tnp Tnp
T
 ) /( )  ( 20  np ) /( np )  (T200  T20 ) / Tnp ,
Tr
Tr
Tr
Tr Tr
Tr
where T200 , and T20 are the light intensities transmitting through the sample at delay 200ps
and 20ps, respectively. Tr is the reference intensity, and Tnp is the intensity before pump.
The pump excites about 2% population initially. According to the Beer-Lambert Law, the
transmittance–pp signal changes about 2.3%, caused by the population change. Now take
the benzonitrile as an example. The signal at 200ps is ~26% of the initial one, while at
20ps, it is about 18%. These give the pp signal to be 0.023*(0.26  0.18)  0.18% .
Energy exchanges cause the signal ~8% of initial population smaller, resulting in total
0.36% bleaching by heating. In the temperature dependent IR measurements, the
transmittance change between 250C to 30 0C is ~0.02. If we assume the change with
temperature is linear, then the pp signal difference between 200ps and 20ps is ~1K. The
temperature measurements and the excited population estimations are not very precise.
The estimated uncertainty would be 0.5~2K. The value estimated here is quite consistent
with Dlott et al’s work1.
(
(1)
Deak, J. C.; Iwaki, L. K.; Dlott, D. D. Journal of Physical Chemistry A
1998, 102, 8193-8201.
6