氨温度计的稳健性
On the robustness of the ammonia thermometer
摘要：
氨转化线经常被用作探测稠密ISM中的物理条件。前两个准亚稳（转动）能级之间的激发温度是气体动力学温度的一个很好的探针。然而，这种氨温度计的校准取决于与H2的碰撞速率的准确性。在这里，我们提出了新的碰撞率ortho-NH3和para-NH3碰撞para-H2（J=0），我们调查这些新的速率对氨的激发的影响。散射计算采用一种新的、高精度的势能面，在耦合簇CCSD（T）水平上用基组外推法计算。获得了J <= 3的氨能级的所有跃迁的速率和5-100 K范围内的动力学温度。我们发现，氨温度计的校准曲线-它涉及到所观察到的激发温度之间的前两个准亚稳态水平的气体动力学温度-不改变显着，当使用这些新的速率。因此，氨温度计的校准似乎是稳健的。新速率对反转和旋转反转跃迁的激发温度的影响也很小。
英文摘要：
Ammonia inversion lines are often used as probes of the physical conditions in the dense ISM. The excitation temperature between the first two para metastable (rotational) levels is an excellent probe of the gas kinetic temperature. However, the calibration of this ammonia thermometer depends on the accuracy of the collisional rates with H2. Here we present new collisional rates for ortho-NH3 and para-NH3 colliding with para-H2 (J=0) and we investigate the effects of these new rates on the excitation of ammonia. Scattering calculations employ a new, high accuracy, potential energy surface computed at the coupled-cluster CCSD(T) level with a basis set extrapolation procedure. Rates are obtained for all transitions involving ammonia levels with J <= 3 and for kinetic temperatures in the range 5-100 K. We find that the calibration curve of the ammonia thermometer -- which relates the observed excitation temperature between the first two para metastable levels to the gas kinetic temperature -- does not change significantly when these new rates are used. Thus, the calibration of ammonia thermometer appears to be robust. Effects of the new rates on the excitation temperature of inversion and rotation-inversion transitions are also found to be small.
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