Cappa Christopher D, Lovejoy Edward R, Ravishankara A R
Earth System Research Laboratory, NOAA, Boulder, Colorado 80305, USA.
J Phys Chem A. 2008 May 1;112(17):3959-64. doi: 10.1021/jp710586m. Epub 2008 Mar 19.
Temperature-dependent vapor pressures of the even-numbered alkanoic monoacids from C8-C18 were measured using temperature-programmed desorption (TPD). In TPD, the evaporation rates from the samples are directly measured and the vapor pressures are subsequently determined from the Hertz-Knudsen equation. Our measurements indicate that the vapor pressures of the solid even-numbered alkanoic acids decrease monotonically with increasing carbon number by more than 6 orders of magnitude going from C8 to C18. The enthalpies of sublimation increase monotonically with carbon number, from approximately 110 to 205 kJ/mol. The liquid-phase vapor pressure was measured for oleic acid, a C18 alkenoic acid. Comparison to the estimated liquid-phase vapor pressure for the corresponding C18 alkanoic acid indicates that the liquid-phase vapor pressures of these two compounds are identical. Our measured solid-phase vapor pressures for the C14 and larger alkanoic acids are lower than in previous studies. We attribute these differences to the influence of residual solvent molecules on the previous measurements, which cause the measured vapor pressures to be too large.
使用程序升温脱附（TPD）测量了C8 - C18偶数链烷单酸的温度依赖性蒸气压。在TPD中，直接测量样品的蒸发速率，随后根据赫兹 - 克努森方程确定蒸气压。我们的测量表明，固体偶数链烷酸的蒸气压随着碳原子数的增加而单调下降，从C8到C18下降超过6个数量级。升华焓随碳原子数单调增加，从约110 kJ/mol到205 kJ/mol。测量了油酸（一种C18链烯酸）的液相蒸气压。与相应C18链烷酸的估计液相蒸气压相比，表明这两种化合物的液相蒸气压相同。我们测量的C14及更大链烷酸的固相蒸气压低于先前的研究。我们将这些差异归因于残留溶剂分子对先前测量的影响，这导致测量的蒸气压过大。
