We have conducted a OH 18 cm survey toward 141 molecular clouds in various environments, including 33 optical dark clouds, 98 Planck Galactic cold clumps (PGCCs), and 10 Spitzer dark clouds with the Arecibo telescope. The deviations from local thermal equilibrium are common for intensity ratios of both OH main lines and satellite lines. Line intensity of OH 1667 MHz is found to correlate linearly with visual extinction when is less than 3 mag. It was converted into OH column density by adopting the excitation temperature derived from Monte Carlo simulations with 1σ uncertainty. The relationship between OH abundance X(OH) relative to H₂ and is found to follow an empirical formula, Linear correlation is found between OH and ¹³COintensity. Besides, nonthermal velocity dispersions of OH and ¹³COare closely correlated. These results imply tight chemical evolution and spatial occupation between OH and ¹³CO. No obvious correlation is found between column density and nonthermal velocity dispersion of OH and H i narrow self-absorption (HINSA), indicating different chemical evolution and spatial volume occupation between OH and HINSA. Using the age information of HINSA analysis, OH abundance X(OH) is found to increase linearly with cloud age, which is consistent with previous simulations. Fourteen OH components without corresponding CO emission were detected, implying the effectiveness of OH in tracing the “CO-dark” molecular gas.

我们使用Arecibo望远镜对141种在各种环境中的分子云进行了OH 18 cm调查，包括33光学暗云，98普朗克银河冷团（PGCC）和10 Spitzer暗云。对于OH主干线和卫星干线的强度比，局部热平衡的偏差是常见的。当小于3 mag时，发现OH 1667 MHz的线强度与消光线性相关。通过采用具有1σ不确定度的蒙特卡洛模拟得出的激发温度，将其转换为OH柱密度。OH丰度之间的关系X（OH）相对于ħ ₂和被发现遵循的经验式，在OH和¹³ CO强度之间发现线性相关。此外，OH和¹³ CO的非热速度分散密切相关。这些结果暗示了OH和¹³ CO之间的紧密化学演化和空间占据。在OH和H i的窄热吸收和窄热吸收之间没有发现明显的相关性，表明OH之间的化学演化和空间体积占有不同和HINSA。使用HINSA分析的年龄信息，OH含量X发现（OH）随云龄线性增加，这与以前的模拟是一致的。检测到14种没有相应CO释放的OH组分，这表明OH在追踪“ CO暗”分子气体中的有效性。