VIBRATIONAL OVERTONE SPECTRA OF C 2 H 6 AND C 2 H 4 IN CRYOGENIC LIQUIDS Helena Diez-y-Riega and Carlos Manzanares Baylor University 2009

High vibrational levels of C 2 H 4 and C 2 H 6 in cryogenic liquid solvents A collection of vibrational overtone spectra of ethylene and ethane in cryogenic solutions.  v=1-6 hydrocarbonmole fraction x10 -3 solvent (liquid)Temperature ethane22argon92 K ethylene0.76argon90 K ethylene1.39krypton120 K Experimental frequencies Local-mode parameters for the different C-H oscillators depending on the hydrocarbon

Experimental setup FT-IR

 v=2  v=3  v=4  v=5 Vibrational overtone spectra of ethane in liquid argon at 92K. 2.2% or 22x10 -3

1390 ppm or 1.39x10 -3  v=2  v=3 x10  v=4 x30

Integrated intensity at maximum absorbance 6142 cm-1

 v=1 142 ppm  v=2 760 ppm  v=3 x30  v=4 x 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, G, G, 6-31+G(d) and (3df,2pd) 1.Geometry optimization followed by determination of harmonic and anharmonic frequencies in gas phase at 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

C 2 H 4 /Ar   r exp   r calc. C 2 H 4 /Kr  Kr exp.  Kr calc. \cm -1 FUNDAMENTAL      FIRST OVERTONE                                           ( X = Ar, Kr)

 v= wavenumber (cm -1 ) Absorbance (a.u.) C 2 H 4 gas C 2 H 4 /Ar C 2 H 4 /Kr gasC 2 H 4 /Ar   r exp C 2 H 4 /Kr  Kr exp. \cm [3,0,0,0] / [3,0,0,0] [2,0,0,0]        [1,1,0,0] [2,1,0,0] 9108 [2,1,0,0]

harmonic frequency (cm -1 ) anharmonicity (cm -1 ) C 2 H 4 gas* C 2 H 4 in Ar sol C 2 H 4 Kr sol

v Thermal lens v=0 v=6

Thermal Lens Experimental setup

 v=6 of ethylene in cryogenic liquids C 2 H 4 in liquid Kr (120K) C 2 H 4 in liquid Ar (92K)

 v=6 of ethylene in cryogenic liquids Kr sol. Ar sol. center (cm-1)FWHM(cm-1)center (cm-1)FWHM (cm-1)

Summary Vibrational overtones of the C-H oscillators (  v=1-6) have been recorded between 2500 and cm -1 for ethane and ethylene dissolved in liquid argon and krypton. Concentrations in the range mole fraction were measured Solubility of C 2 H 4 in liquid argon is approximately 761 ppm at 90 K. The integrated absorption of the 6142 cm -1 band (1 st overtone) was used for this determination.

Summary Peak frequency shifts (  ) have been observed from gas phase to solution in both C 2 H 4 and C 2 H 6 Ethylene in liquid krypton showed higher  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.  is explained by the change of the harmonic frequencies and anharmonicities in solution. Summary

Acknowledgment Dr. C. E. Manzanares Yasnahir Perez-Delgado David Camejo Jenny Barroso Abraham Rodriguez Dr. Alfredo Lopez-Calvo Dr. Ansgar Brock Robert A. Welch Foundation Baylor University