AlH lines in the blue spectrum of Proxima Centauri

Abstract

The recently computed ExoMol line lists for isotopologues of AlH are used to analyse the blue spectrum (4000–4500 Å) of Proxima Cen (M5.5 V). Comparison of the observed and computed spectra enables the identification of a large number of 27AlH lines of the A 1Π –X 1Σ+ band system: The spectral range covering 1-0, 0-0, and 1-1 bands are dominated by clearly resolved AlH lines. We reveal the diffuse nature of transitions close to the dissociation limit which appears in the form of increasingly wider (up to 5 Å) and shallower (up to the continuum confusion limit) AlH line profiles. The predicted wavelengths of AlH diffuse lines are systematically displaced. The effect of broadening by predissociation states on the line profiles is included by increasing the radiative damping rate by up to 5 orders of magnitude. We determine empirical values of damping rates for a number of the clean 0-0 Q-branch transitions by comparing the observed and synthetic stellar spectra. We find excellent agreement between our damping rates and lifetimes available in the literature. A comparison of 27Al1H ExoMol and REALH spectra shows that the observed spectrum is better described by the ExoMol line list. A search for 26Al1H lines in the Proxima Cen spectrum does not reveal any notable features; giving an upper limit of 27Al1H /26Al1H >100.

Formation of AlO, AlOH, and Al(OH)3 in the Interstellar Medium and Circumstellar Envelopes of AGB Stars

“…AlH is chosen due to its simplicity and observation in the atmosphere of Proxima Centauri. 54 The addition of the hydroxyl radical (OH) results in the formation of the stable intermediate cis-HAlOH, which can lose two hydrogen atoms as H 2 to produce AlO with a net exothermicity of 51.3 kcal mol −1 . Even though the transition state lies nearly 55 kcal mol −1 above the previous intermediate, it still lies 38.9 kcal mol −1 below the energies of the initial reactants.…”

“…Figure shows the proposed reaction pathway between aluminum hydride (AlH) and the small, oxygen-containing molecules OH, H 2 O, and AlO. AlH is chosen due to its simplicity and observation in the atmosphere of Proxima Centauri . The addition of the hydroxyl radical (OH) results in the formation of the stable intermediate cis -HAlOH, which can lose two hydrogen atoms as H 2 to produce AlO with a net exothermicity of 51.3 kcal mol –1 .…”

“…The reaction of aluminum hydride with water has recently provided a promising pathway to the formation of larger, hydrated aluminum oxide clusters, 53 but AlH 3 has yet to be conclusively observed toward any astronomical sources. However, the simpler diatomic, AlH, has been observed in the atmosphere of our nearest stellar neighbor, 54 rendering this molecule a possible reactant for the creation of AlO or AlOH in circumstellar and interstellar environments.…”

Theoretical study on spectroscopic properties of 10 Λ-S and 26 Ω states for AlH molecule

“…计算得到的光谱常数和跃迁数据与现有的实验值符合很好. 研究发现:1) A 1 P 1 -(0, 0), (0, 1), (0, 2), (1, 0), (1,1), (1,2), (1,3), (1,4)和(1, 5)带Q(J'')支的跃迁比较强, 随着J''的增大, Du = 0带的爱因 斯坦A系数和振动分支比值逐渐减小, 加权的吸收振子强度值逐渐增大; Du ≠ 0带的爱因斯坦A系数、振 动分支比和加权的吸收振子强度值逐渐增大; 2) A 1 P 1 态u' = 0和1能级的辐射寿命随着J'的增大而缓慢增 大; 3) AlH分子的A 1 P 1 (u' = 0和1, J' = 1, +) → (u'' = 0-3, J'' = 1, -)跃迁满足双原子分子激光冷 却的准则, 即对角化分布的振动分支比, A 1 P 1 (u' = 0和1, J' = 1, +)态极短的辐射寿命, , a 3 P 1 和a 3 转动光谱研究了AlH分子的X 1 S + , a 3 P, A 1 P, b 3 S -, C 1 S + 态的光谱性质, 并在红外线、可见光和紫外 线中识别出许多带 [4,5,7−21] . 例如, Halfen和Ziurys [5] 利用太赫兹直接吸收光谱测量了755 GHz附近 AlH分子X 1 S + 态J = 2 ← 1的转动光谱.…”

“…带和C 1 S + → A 1 P (0, 0)和(1, 1)带, 紫外区域 C 1 S + → X 1 S + (0, 0), (1, 1)和 (1, 2)带 . 最 近 , Szajna研究组 [17] 采用傅里叶变换光谱仪观测到 AlH的高分辨率可见光发射光谱, 覆盖了A 1 P → X 1 S + 系统的(0, 0), (0, 1), (0, 2), (1, 0), (1,1), (1,2),…”