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

Experimental setup FT-IR

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)

v

Thermal lens T

0

v=0

v=6

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

C2H4 in liquid Kr (120K)

C2H4 in liquid Ar (92K)

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

Acknowledgment

Dr. C. E. Manzanares

Yasnahir Perez-DelgadoDavid CamejoJenny Barroso

Abraham Rodriguez

Dr. Alfredo Lopez-CalvoDr. Ansgar Brock

Robert A. Welch Foundation

Baylor University