On finite groups isospectral to U ₃(3)

The spectrum of a finite group is the set of all its element orders. A finite group G is called critical with respect to a subset ω of natural numbers, if ω coincides with the spectrum of G and does not coincide with the spectrum of any proper section of G. We study the structure of groups isospectral to a simple unitary group PSU(3, 3). In particular, we give a description of the finite groups critical with respect to the spectrum of PSU(3, 3).