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VIBRATIONAL OVERTONE SPECTRA OF C2H6 AND C2H4 IN
CRYOGENIC LIQUIDS
Helena Diez-y-Riega and Carlos ManzanaresBaylor University
2009
High vibrational levels of C2H4 and C2H6 in cryogenic liquid solvents
A collection of vibrational overtone spectra of ethylene and ethane in cryogenic solutions. Dv=1-6
hydrocarbon mole fraction x10-3 solvent (liquid) Temperature
ethane 22 argon 92 K
ethylene 0.76 argon 90 K
ethylene 1.39 krypton 120 K
Experimental frequencies
Local-mode parameters for the different C-H oscillators depending on the hydrocarbon
0.00
0.50
1.00
1.50
2.00
2.50
4000 6000 8000 10000 12000 14000 16000
Wavenumber / cm-1
Dv=2
Dv=3
Dv=4
Dv=5
Vibrational overtone spectra of ethane in
liquid argon at 92K.
2.2% or 22x10-3
4000 5000 6000 7000 8000 9000 10000 11000 120000.0
0.1
0.2
0.3
0.4
0.5
Ethylene in liquid Kr at 121 K
wavenumber (cm-1)
Abso
rban
ce (a
.u.)
1390 ppm or 1.39x10-3
Dv=2
Dv=3x10
Dv=4x30
0 200 400 600 800 1000 12000
0.5
1
1.5
2
2.5
3
3.5
4
4.5Solubility of ethylene in liquid Ar at 90K
Concentration of ethylene (ppm)
Inte
grat
ed a
bsor
banc
e (a
.u.)
S =761ppm or 7.6x10-4
Integrated intensity atmaximum absorbance
6142 cm-1
2500 3500 4500 5500 6500 7500 8500 9500 10500 11500 125000.0
0.1
0.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0 Ethylene in liquid Ar at 90 K
wavenumber (cm-1)
Abso
rban
ce (a
.u.)
Dv=1142 ppm
Dv=2760 ppm
Dv=3x30
Dv=4x50
760 ppm or 7.60x10-4
Fundamental and first overtone transitions
Gaussian 03. Density functional theory (DFT) level using the exchange correlation hybrid functional Becke’s 3-parameters and Lee-Yang-Parr (B3LYP)
Different basis set: 6-31G, 6-311G, 6-311+G, 6-311++G, 6-31+G(d) and 6-311++(3df,2pd)
1. Geometry optimization followed by determination of harmonic and anharmonic frequencies in gas phase at 298.15 K
2. Geometry optimization in the presence of the solvent using the integral equation formalism of the polarizable continuum model (IEFPCM)
3. Calculation of harmonic and anharmonic frequencies using the IEFPCM of the optimized molecular structure in the presence of the solvent at the temperature corresponding to liquid argon (90K) or liquid krypton (120K)
Tomasi’s PCM model
5500 5750 6000 62500.00
0.10
0.20
C2H4/Ar DwAr exp DwAr calc. C2H4/Kr DwKr exp. DwKr calc. \cm-1
FUNDAMENTAL 2984 4 13 5 n11
3072 5 1 -20 n2+n12 3099 7 14 6 n5
FIRST OVERTONE 5725 10 5719 16 n5+n12+n6
5784 4 5779 9 9 n1+n3+n12
5835 5830 n11+n12+n6
5910 9 33 5905 15 10 n11+n2+n3
5917 10 5911 16 n0+n2+n6
5940 10 11 5933 17 9 n1+n11
5985 0 2 5978 7 10 n5+n11
6060 12 6052 20 n1+n2+n12
6091 25 6084 11 n1+n9
6142 9 17 6135 16 9 n5+n9
6187 13
Xsolventgas freqfreq
(X = Ar, Kr)
Dv=3
90008500 wavenumber (cm-1)
Abso
rban
ce (a
.u.)
C2H4 gas
C2H4 /Ar
C2H4 /Kr
gas C2H4/Ar DwAr exp C2H4/Kr DwKr exp. \cm-1
8619 8616 3 8614 5 [3,0,0,0] /2n1+n11
8734 8721 148755 8738 17 8728 26 [3,0,0,0] 8770 8774 -3 8766 5 [2,0,0,0]+2n12
8790 8790 0 11n +2n12+n2+n3 8886 8866 20 8851 358976 8967 10 8957 19 [1,1,0,0]+2n12 9002 8982 20 9001 1 [2,1,0,0]
9108 [2,1,0,0]
harmonic
frequency (cm-1)anharmonicity
(cm-1)C2H4 gas* 3170 -59C2H4 in Ar sol. 3140 -56.4C2H4 Kr sol. 3132 -55.3
3.5 4 4.5 5 5.5 6 6.5 7 7.52700
2800
2900
3000
3100
3200
Birge-Sponer plot of ethylene in L-Kr
V+1
DE/v
(cm
-1)
Thermal Lens Experimental setup
Argon laser, 514 nm Dye laser
Stepper motor
Function generator
Argon probe laser, 488 nm
Photodiode
Cryopump
Lock-in amplifier
Pre-amplifier
Lock-in amplifier
PMT Power supply
XYZ stage
PMT
IF
Iris
BF
L
L
RF
M
DF
Shutter
Cryostat & sample cell
Data acquisition & control
Dv=6 of ethylene in cryogenic liquids
Kr sol. Ar sol. center (cm-1) FWHM(cm-1) center (cm-1) FWHM (cm-1)
16131 460 16161 11316230 453 16242 5016447 187 16463 19616560 219 16633 19416768 281 16753 65
16840 120
Summary
Vibrational overtones of the C-H oscillators (Dv=1-6) have been recorded between 2500 and 17000 cm-1 for ethane and ethylene dissolved in liquid argon and krypton. Concentrations in the range 10-3 - 10-4 mole fraction were measured
Solubility of C2H4 in liquid argon is approximately 761 ppm at 90 K. The integrated absorption of the 6142 cm-1 band (1st overtone) was used for this determination.
Summary
Peak frequency shifts (Dw) have been observed from gas phase to solution in both C2H4 and C2H6
Ethylene in liquid krypton showed higher Dw than solutions in liquid argon. These red-shifts are explained by the change in local mode parameters from the gas phase to liquid solution.
DFT frequency analysis of the fundamental and first vibrational overtone transitions of ethylene was done.
1. Calculated (DFT) anharmonic and harmonic (scaled) frequencies in gas phase agree with the experimental results.
2. Calculations (IEFPCM) of harmonic frequencies in the presence of the solvent did not show any shift in the frequencies.
3. Anharmonic frequency calculations in the gas phase and in the presence of the solvent showed a shift to lower energies.
Dw is explained by the change of the harmonic frequencies and anharmonicities in solution.
Summary
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