多组分天然气水合物在海底沉积层中稳定区及存在区的预测

本文研究了多组分天然气在海底沉积层中稳定区和存在区的一些特点. 首先,考虑盐的浓度的影响,建立了天然气含有甲烷和丙烷两种组分的水合物形成的相变曲线,即温度和压力关系曲线,同时也建立了甲烷和丙烷两种组分天然气溶解度的加权关系. 运用水合物预测模型,计算了多组分天然气水合物在海底沉积层中的稳定区及存在区,并同单组分的甲烷水合物的结果进行了对比.计算表明：两种组分的天然气水合物的稳定区与单组分甲烷水合物的稳定区有较大差别,这归因于丙烷对相变曲线大的影响;当天然气浓度大于对应的溶解度时,水合物将形成,由此决定了存在区域;稳定区和存在区范围都受到丙烷含量的较大影响,盐度的增大则减少了稳定区范围. 最后对甲烷分别与其他气体（例如二氧化碳,乙烷和硫化氢等）组合的天然气水合物形成的稳定区范围进行了简要的分析.     

Titan's prolific propane: The Cassini CIRS perspective

Although propane gas (C₃H₈) was first detected in the stratosphere of Titan by the Voyager IRIS infrared spectrometer in 1980, obtaining an accurate measurement of its abundance has proved difficult. All existing measurements have been made by modeling the ν₂₆ band at : however, different analyzes over time have yielded quite different results, and it also suffers from confusion with the strong nearby ν₅ band of acetylene. In this paper we select large spectral averages of data from the Cassini Composite Infrared Spectrometer (CIRS) obtained in limb-viewing mode at low latitudes (30^°S-30^°N), greatly increasing the path length and hence signal-to-noise ratio for optically thin trace species such as propane. By modeling and subtracting the emissions of other gas species, we demonstrate that at least six infrared bands of propane are detected by CIRS, including two not previously identified in Titan spectra. Using a new linelist for the range 1300-1400 cm^-1, along with an existing GEISA list, we retrieve propane abundances from two bands at 748 and 1376 cm^-1. At 748 cm^-1 we retrieve 4.2±0.5×10^-7 (1-σ error) at 2 mbar, in good agreement with previous studies, although lack of hotbands in the present spectral atlas remains a problem. We also determine 5.7±0.8×10^-7 at 2 mbar from the 1376 cm^-1 band — a value that is probably affected by systematic errors including continuum gradients due to haze and also an imperfect model of the ν₆ band of ethane. This study clearly shows for the first time the ubiquity of propane's emission bands across the thermal infrared spectrum of Titan, and points to an urgent need for further laboratory spectroscopy work, both to provide the line positions and intensities needed to model these bands, and also to further characterize haze spectral opacity. The present lack of accurate modeling capability for propane is an impediment not only for the measurement of propane itself, but also for the search for the emissions of new molecules in many spectral regions.