The discovery of aluminum monohydroxide (AlOH) was reported in 2010 by
Tenebaum 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].