Optical transitions between surface states associated with dangling bonds in $\mathrm{Si}\mathrm{}\left(111\right)2\times 1$ have been measured by means of reflection anisotropy spectroscopy in the near infrared. The results confirm those previously obtained with other optical techniques (namely surface differential reflectivity and photothermal deflection spectroscopies). The method does not require oxidation of the surface and thus opens the way to studying a number of problems in surface physics, including the temperature dependence of surface transitions in $\mathrm{Si}\mathrm{}\left(111\right)2\times 1$ and $\mathrm{Ge}\mathrm{}\left(111\right)2\times 1.$

• Received 28 March 2002

DOI:https://doi.org/10.1103/PhysRevB.66.153307