Abstract The rotational spectrum of propionitrile (ethyl cyanide, C2H5CN) in the two lowest excited vibrational states, v 13 = 1 and v 21 = 1 , was studied in detail. The compiled experimental data set consisted of published line lists, lines measured from published spectra up to 645 GHz, and new measurements at frequencies from 8 to 331 GHz. The two states are subject to considerable mutual interaction but application of a- and b-axis Coriolis coupling model to the measured A-symmetry internal rotation substate transitions was found to be successful. A total of over 1900 transitions were fitted for J values up to 76 and K a up to 24, resulting in determined vibrational separation between the two states Δ E = 6.2070246 ( 14 ) cm−1, and Coriolis coefficients | ζ 13 , 21 a | = 0.378, | ζ 13 , 21 b | = 0.127, in good agreement with quantum chemistry calculations. The new line catalog was used to model ALMA spectra of Titan’s atmosphere from 2016, fitting many weak lines not previously modeled. By including the vibrationally excited lines of C2H5CN and a new partition function, we derive a disk-averaged volume mixing ratio estimate in 2016 of 7.8 ± 0.2 ppb assumed constant above 300 km.

中文翻译：

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实验室和泰坦上两种最低激发振动态的丙腈

摘要 详细研究了丙腈（乙基氰，C2H5CN）在两个最低激发振动态v 13 = 1 和v 21 = 1 下的旋转光谱。编译后的实验数据集包括已发布的谱线列表、从已发布的高达 645 GHz 的光谱中测量的谱线，以及在 8 至 331 GHz 频率下的新测量值。这两种状态受到相当大的相互作用，但发现将 a 轴和 b 轴科里奥利耦合模型应用于测量的 A 对称内部旋转子状态转换是成功的。对于高达 76 的 J 值和高达 24 的 K a ，总共拟合了 1900 多个跃迁，从而确定两个状态之间的振动分离 Δ E = 6.2070246 ( 14 ) cm-1 和科里奥利系数 | ζ 13 , 21 a | = 0.378, | ζ 13 , 21 b | = 0.127, 与量子化学计算非常吻合。新的线目录用于对 2016 年泰坦大气的 ALMA 光谱进行建模，拟合许多以前未建模的弱线。通过包括 C2H5CN 的振动激发线和新的分区函数，我们推导出 2016 年磁盘平均体积混合比估计值为 7.8 ± 0.2 ppb，假设在 300 公里以上为常数。