Thermal Lens in Cryogenic Solutions: Vibrational overtone spectra of benzene in liquid ethane Helena Diez-y-Riega and Carlos E. Manzanares Department of Chemistry and Biochemistry Baylor University

This natural color image shows Titan's upper atmosphere: an active place where methane molecules are being broken apart by solar ultraviolet light . The products combine to form compounds like ethane and acetylene. N2 90% (78%) CH4 10% (1.7ppm) Image Credit: NASA/JPL/Space Science Institute

This north polar image of Titan was acquired by Cassini’s radar instrument on May 12, 2007. The liquid most likely a combination of methane and ethane, appears very dark to the radar instrument Credit: NASA/JPL

Laboratory simulation : the lakes of Titan Low temperature (90 -120 K) Low concentration of unsaturated hydrocarbons Solubility of benzene in liquid CH4, C2H6, N2 and Ar Absorption spectra of benzene dissolved in liquid ethane and methane

Measuring the solubility VARIAN / CARY 50 Bio UV-Vis Spectrophotometer (l=190nm-1100nm)

UV spectrum of benzene 69 ppm in liquid ethane at 102 K

C-H Du=6 vibrational overtone of benzene 16481 cm-1 Thermal lensing: C-H Du=6 vibrational overtone of benzene 16481 cm-1 u=6 u=0 H

Experimental setup COAXIAL CONFIGURATION Pass step Pump beam cut Io It Pump beam Probe beam A. Lopez-Calvo and C. E. Manzanares J. Phys. Chem. A, 110 (35), 10427 -10434

Thermal Lens C-H Du=6 vibrational overtone benzene in CCl4 at 298K TLS (arb. units) DEmax=16450 cm-1 1% DEmax=16450 cm-1 0.1% 0.01% =100ppm DEmax=16471 cm-1

Thermal Lens C-H Du=6 vibrational overtone benzene 2% in hexane at 298K, Pex=120mW TLS (arb. units) DEmax = 16431 cm-1

Thermal Lens Liquid ethane 99% at 100 K* Liquid benzene 99.99% at 298 K Du=6 *A. Lopez-Calvo and C. E. Manzanares: J. Phys. Chem. A 2008, 112, 1730-1740

Thermal Lens C-H Du=6 vibrational overtone benzene 58 ppm in liquid ethane at 120K, Pex= 220mW DEmax=16498 cm-1 TLS (au)

Thermal Lens C-H Du=6 vibrational overtone benzene in liquid ethane, Pex= 600mW DEmax=16467 cm-1 19 Torr = 48 ppm, 100 K TLS (au) DEmax=16498 cm-1 19 Torr = 50 ppm, 120 K TLS (au)

V = 6 (600 nm) (355 nm) (223 nm)

Summary The solubility of benzene in liquid ethane has been measured using UV spectroscopy: C-H Du=6 vibrational overtone spectra of solutions of benzene have been obtained benzene in carbon tetrachloride at room temperature in concentrations as low as 100 ppm. benzene dissolved in hexane at room temperature. This spectrum has evidenced the viability of using a saturated hydrocarbon as a solvent. Temperature (K) Solubility (ppm) 102 76 132 145 162 156

Summary The weak Du=6 C-H vibrational overtone spectra of benzene dissolved in liquid ethane at 120K and 100K, and very low concentrations (~50 ppm) have been obtained. We have shown that it is possible to study overtone spectra of molecules in solution at the solubility level (ppm) of cryogenic liquids.

Acknowledgement Dr. C. E. Manzanares Dr. Alfredo Lopez-Calvo Yasnahir Perez-Delgado Nicholas Hernandez David Camejo Jenny Barroso Robert A. Welch Foundation Baylor University