Sloan G C, Bregman J D, Geballe T R, Allamandola L J, Woodward C E
NASA Ames Research Center, Moffett Field, CA 94035-1000, USA.
Astrophys J. 1997 Jan 10;474(2 Pt 1):735-40. doi: 10.1086/303484.
Long-slit spectra across the Orion Bar reveal significant differences in the spatial behavior of the components of the 3 microns polycyclic aromatic hydrocarbon (PAH) spectrum. The strong PAH band at 3.29 microns generally decreases exponentially with distance from the ionization front into the molecular cloud (scale height approximately 12"), although excesses appear approximately 10" and 20" behind the ionization front, close to layers of H2 and CO emission, respectively. The 3.40 microns PAH feature separates into two components with very different spatial distributions. The main component (at 3.395 microns), along with the 3.51 microns band and the PAH plateau (3.3-3.6 microns), shows excess emission approximately 10" and approximately 20" behind the ionization front, stronger than the excesses in the 3.29 microns band. The extra component of the 3.40 microns band, which peaks at approximately 3.405 microns, has a spatial distribution very similar to the H2 emission. Aromatic C-H stretches in PAHs most likely produce the 3.29 microns feature. Aliphatic C-H stretches in either attached methyl side-groups or superhydrogenated PAHs, or perhaps both, could produce the complicated spectral and spatial structure at 3.40 microns.
横跨猎户座棒状星云的长缝光谱揭示了3微米多环芳烃（PAH）光谱各成分空间行为的显著差异。3.29微米处的强PAH带通常随着离电离前沿进入分子云的距离呈指数下降（标高约12英寸），不过在电离前沿后方约10英寸和20英寸处出现过量，分别靠近H₂和CO发射层。3.40微米的PAH特征分裂为两个具有非常不同空间分布的成分。主要成分（在3.395微米处），连同3.51微米带和PAH平台（3.3 - 3.6微米），在电离前沿后方约10英寸和约20英寸处显示出过量发射，比3.29微米带中的过量发射更强。3.40微米带的额外成分，在约3.405微米处达到峰值，其空间分布与H₂发射非常相似。PAH中的芳香族C - H伸缩振动很可能产生3.29微米的特征。连接的甲基侧基或超氢化PAH中的脂肪族C - H伸缩振动，或者可能两者都有，可能产生3.40微米处复杂的光谱和空间结构。
