We have performed electronic-structure calculations using the extended tight-binding method for two-dimensional isolated layers of CO molecules corresponding to the ordered arrays formed on a Pd(100) surface. We find that the calculated width and shape of the 4-derived band is in good agreement with angular-resolved photoemission results from this system. The calculated widths of the 5- and 1-derived bands are much greater than that of the 4-derived band, reflecting their more delocalized nature. In the photoemission experiment some dispersion is detected on the 5+1composite level but it was not possible to separate out the component bands. © 1979 The American Physical Society.