  Photoelectron momentum distributions from strong-field ionization of carbonyl
sulfide with 800 nm central-wavelength laser pulses at various peak intensities
from $4.6$ to $13\times10^{13}$ W/cm$^2$ were recorded and analyzed regarding
resonant Rydberg states and photoelectron orbital angular momentum. The
evaluation of the differentials of the momentum distributions with respect to
the peak intensity highly suppressed the impact of focal volume averaging and
allowed for the unambiguous recognition of Freeman resonances. As a result,
previously made assignments of photoelectron lines could be reassigned. An
earlier reported empirical rule, which relates the initial state's orbital
momentum and the minimum photon expense to ionize an ac Stark shifted atomic
system to the observable dominant photoelectron orbital momentum, was confirmed
for the molecular target.
