Solubility and spectroscopy of unsaturated hydrocarbons in cryogenic solvents.
The exploration of Saturn's moon, Titan has revealed an atmosphere rich in nitrogen as in Earth, and has established the presence of gaseous methane. Data from the Cassini-Huygens mission have shown the existence of liquid bodies of methane and ethane, such as lakes and rivers with geological structures similar to Earth, with bays, islands, and channels. Moreover, the Cassini-Huygens mission has shown strong evidence that Titan's surface and atmosphere have an active hydrological cycle alike, with condensed hydrocarbons instead. Although identification of chemical species is hard, many organic molecules have been detected in the atmosphere, and in icy form on the surface. Spectroscopic properties and solubility of many unsaturated hydrocarbons dissolved in liquid methane and ethane is unknown. Thus, in this work, vibrational spectroscopy in the IR-NIR-Vis of small organic molecules such as benzene, ethene, 2-methyl-1,3-butadiene (isoprene), and formaldehyde dissolved in liquid ethane, rare gases, and nitrogen under Titan's conditions (low temperatures, and concentrations in the order of 10⁻⁴ mole fraction) are presented. Our studies indicate that the presence of the solvent interacting with the solute produces frequency shift and change in the linewidth from that of the gas phase. Additionally, solubilities of unsaturated hydrocarbons in liquid ethane and liquid argon have been measured. In order to study the weak fifth CH vibrational overtone of the selected molecules, Fourier Transform spectroscopy is not sensible enough. Thermal Lens spectroscopy has been found to be a very sensitive technique, good for detecting samples of low concentration in transparent solutions. In addition to the traditional double-beam configuration, whose absorption process is carried out with one photon absorption, we have also developed a new triple-beam thermal lens apparatus in a collinear configuration, in order to enhance the thermal lens signal upon two photon absorption.