Computational Molecular Spectroscopy:
Fe-containing Molecules of Astrochemical Interest
Tsuneo Hirano,1 Umpei Nagashima,2 and Per Jensen3
1)
Ochanomizu University, Japan.
2)Foundation for Computational Science (FOCUS), Japan.
3)
Bergische Universität, Germany
The aim of Astrochemistry is to elucidate how molecules have evolved in space, i.e., todetermine which molecules are there and which reactions have formed them. More than 180
molecules have been detected already. Although Fe is known to have a large cosmic
abundance comparable to those of Mg and Si, the only iron-containing molecules detected in
the cosmic environment so far are FeH in sunspots [1], FeO toward Sgr B2 [2,3]，andFeCN toward IRC +10216 [4]. In 1994, we made a preliminary ab initio calculation for
FeCO as a candidate for observation in interstellar space, but attempts to detect it in space
failed [5,6]. Then we started ab initio calculations on several Fe-containing molecules ofastrochemical interest, including FeC [7], FeN [8], FeS, FeNC [9], FeCN [10], FeOH [11,12],and FeCO [13 (electronic properties)]. We will report here recent progress of computational
molecular spectroscopy on Fe-containing molecules.
For FeCO, we have published a very accurate 3D potential energy surface [14], and reported
many ro-vibrational properties. The calculated rotational constant B0 deviates by only 0.03%
from experimental value. For FeCN, observed by the Ziurys group toward IRC +10216 [4],the electronic ground state was erroneously claimed to be 4∆i [4] simply because rotational
spectrum for the other electronic states was not observed in their laboratory. OurMR-SDCI+Q calculations show that the 4∆i state is higher in energy than the 6∆i state by ca.
4000 cm-1.
FeOH is another possible interstellar molecule candidate, but neither laboratory experiments
nor space observations have been reported. Stimulated by IR cold-chemistry experiments onFeO+ reactions by the Dieter Gerlich group [15], we have calculated the equilibrium
structures and energy levels of FeO, FeO+, and FeOH+. Presently, 3D PES calculations for
FeOH+ are in progress.
We hope these studies will be helpful for identification of more Fe-containing molecules inspace.
References.

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