Pardo J R, Bermúdez C, Cabezas C, Agúndez M, Gallego J D, Fonfría J P, Velilla-Prieto L, Quintana-Lacaci G, Tercero B, Guélin M, Cernicharo J
Grupo de Astrofísica Molecular, Instituto de Física Fundamental (IFF-CSIC), C/ Serrano 121, 28006 Madrid, Spain.
Centro de Desarrollos Tecnológicos, Observatorio de Yebes (IGN), 19141 Yebes, Guadalajara, Spain.
Astron Astrophys. 2020 Aug 10;640. doi: 10.1051/0004-6361/202038571. eCollection 2020 Aug.
Observations of IRC +10216 with the Yebes 40m telescope between 31 and 50 GHz have revealed more than 150 unidentified lines. Some of them can be grouped into a new series of 26 doublets, harmonically related with integer quantum numbers ranging from =54 to 80. The separation of the doublets increases systematically with , i.e., as expected for a linear species in one of its bending modes. The rotational parameters resulting from the fit to these data are = 290.8844 ± 0.0004 MHz, = 0.88 ± 0.04 Hz, = 0.1463 ± 0.0001 MHz. The rotational constant is very close to that of the ground state of HCN. Ab initio calculations show an excellent agreement between these parameters and those predicted for the lowest energy vibrationally excited state, =1, of HCN. This is the first detection, and complete characterization in space, of vibrationally excited HCN. An energy of 41.5 cm is estimated for the state. In addition, 17 doublets of HCN in the =1 state, for which laboratory spectroscopy is available, have been detected for the first time in IRC+10216. Several doublets of HCN in its =1 state have been also observed. The column density ratio between the ground and the lowest excited vibrational states are ≈127, 9.5, and 1.5 for HCN, HCN, and HCN, respectively. We find that these lowest-lying vibrational states are most probably populated via infrared pumping to vibrationally excited states lying at ≈600 cm. The lowest vibrationally excited states thus need to be taken into account to precisely determine absolute abundances and abundanceratios for long carbon chains. The abundance ratios N(HCN)/N(HCN) and N(HCN)/N(HCN) are 2.4 and 7.7 respectively.
使用耶贝斯40米望远镜在31至50吉赫兹对IRC +10216进行的观测揭示了150多条未识别谱线。其中一些可以归为一个新的由26个双峰组成的系列，与从J = 54到80的整数量子数呈谐波相关。双峰之间的间距随J系统地增加，即如线性分子在其一种弯曲模式下所预期的那样。对这些数据进行拟合得到的转动参数为：A = 290.8844 ± 0.0004兆赫兹，D J = 0.88 ± 0.04赫兹，H J = 0.1463 ± 0.0001兆赫兹。转动常数与HCN基态的转动常数非常接近。从头算计算表明这些参数与HCN最低能量振动激发态v = 1所预测的参数之间有极好的一致性。这是首次在太空中探测并完整表征振动激发的HCN。估计v = 1态的能量为41.5厘米-1。此外，首次在IRC +10216中探测到了v = 1态的17个HCN双峰，其有实验室光谱数据可用。还观测到了v = 1态的几个HCN双峰。对于HCN、HCN和HCN，基态与最低激发振动态之间的柱密度比分别约为127、9.5和1.5。我们发现这些最低的振动态很可能是通过红外泵浦到约600厘米-1的振动激发态而被填充的。因此，为了精确确定长碳链的绝对丰度和丰度比，需要考虑最低的振动激发态。N(HCN)/N(HCN)和N(HCN)/N(HCN)的丰度比分别为2.4和7.7。
