W51 e2中振动激发的甲酸甲酯的检测
Detection of vibrationally excited methyl formate in W51 e2
摘要：
甲酸甲酯在其第一扭转激发态（VT=1，在131 cm-1）的第一次检测到W51 e2。在观察到的光谱范围内，实际上检测到来自激发的甲酸甲酯的所有跃迁（82个跃迁），并且没有丢失强线。激发态的柱密度与基态的柱密度相当。对于7英寸的源尺寸，我们发现激发态的Trot = 104 +/- 14 K和N = 9.4 +4.0/-2.8 x 10^16 cm-2，而基态的Trot = 176 +/- 24 K和N = 1.7 +.2/-.2 x 10^17 cm-2。在所观察到的光谱中还存在来自处于其两个第一激发态（Vt=1，在212 cm-1处的扭转模式）和（Vb=1，在206 cm-1处的CCN面内弯曲模式）的乙腈的线。然而，混合问题阻止了对其丰度的精确估计。关于在W51 e2中检测到的激发态甲酸甲酯和乙基氰的谱线数目，看来大分子的激发态肯定是在分子云光谱测量中大量未识别谱线的原因。
英文摘要：
Methyl formate in its first torsionally excited state (vt=1 at 131 cm-1) is detected for the first time toward W51 e2. All transitions from excited methyl formate within the observed spectral range are actually detected (82 transitions) and no strong lines are missing. The column density of the excited state is comparable to that of the ground state. For a source size of 7'' we find that Trot = 104 +/- 14 K and N = 9.4 +4.0/-2.8 x 10^16 cm-2 for the excited state and Trot = 176 +/- 24 K and N = 1.7 +.2/-.2 x 10^17 cm-2 for the ground state. Lines from ethyl cyanide in its two first excited states (vt=1, torsion mode at 212 cm-1) and (vb=1, CCN in-plane bending mode at 206 cm-1) are also present in the observed spectrum. However blending problems prevent a precise estimate of its abundance. With regard to the number of lines of excited methyl formate and ethyl cyanide detected in W51 e2, it appears that excited states of large molecules certainly account for a large number of unidentified lines in spectral survey of molecular clouds.
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