Iron Complexes as Potential Carriers of Diffuse Interstellar Bands: The Photodissociation Spectrum of Fe+(H2O) at Optical Wavelengths

The fullerene ion
C60+ is the
only carrier of diffuse interstellar bands (DIBs)
identified so far. Transition-metal compounds feature electronic transitions
in the visible and near-infrared regions, making them potential DIB
carriers. Since iron is the most abundant transition metal in the
cosmos, we here test this idea with Fe+(H2O).
Laboratory spectra were obtained by photodissociation spectroscopy
at 80 K. Spectra were modeled with the reflection principle. A high-resolution
spectrum of the DIB standard star HD 183143 served as an observational
reference. Two broad bands were observed from 4120 to 6800 Å.
The 4120–4800 Å band has sharp features emerging from
the background, which have the width of DIBs but do not match the
band positions of the reference spectrum. Calculations show that the
spectrum arises from a d–d transition at the iron center. While
no match was found for Fe+(H2O) with known DIBs,
the observation of structured bands with line widths typical for DIBs
shows that small molecules or molecular ions containing iron are promising
candidates for DIB carriers.

富勒烯离子C60+迄今为止是唯一已知的扩散星际带（DIBs）的载体。过渡金属化合物在可见光和近红外区域表现出电子跃迁，使其成为潜在的DIB载体。鉴于铁是宇宙中最丰富的过渡金属，本研究以Fe+(H2O)为对象，检验了这一设想。在80K的温度下，通过光解光谱获得了实验室光谱。光谱模型采用反射原理进行模拟。DIB标准星HD 183143的高分辨率光谱作为观测参考。在4120至6800Å的范围内观察到了两个宽波段。4120–4800Å波段中，从背景中突显出具有DIB宽度的尖锐特征，但并不与参考光谱的波段位置相匹配。计算表明，该光谱起源于铁中心的d–d跃迁。尽管未发现与已知DIBs相匹配的Fe+(H2O)，但观察到的具有典型DIB线宽的结构化波段表明，含有铁的小分子或分子离子是DIB载体的有利候选。