March 2014

Aluminum Monohydroxide

The discovery of aluminum monohydroxide (AlOH) was reported in 2010 by Tenenbaum and Ziurys in the circumstellar envelope of hypergiant star VY Canis Majoris. The observations were made with the 12 meter telescope at the Arizona Radio Observatory on Kitt Peak. The rotational spectrum of AlOH used to make the detection was reported by Apponi et al. in 1993. As noted in the discovery paper, earlier searches for AlOH in IRC +10216 and Orion-KL were unsuccessful. No further confirming detections have been reported to date.

The large (~158°) but not linear bond angle of AlOH indicates that it is intermediate between a covalently bonded compound (such as H–OH, where the bond angle is less than 110°) and a predominately ionically bonded compound (such as Li–OH, which is linear). The dipole moment of AlOH (0.98 D) indicates a fair degree of charge transfer, but it is much less than LiOH (4.71 D) [RCCSD(T)/aug-cc-pVTZ results for dipole moments].

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