We performed a theoretical study of the electron diffraction patterns that arise from aligning a molecule,
s-tetrazine (C2N4H2), in a high intensity laser field using the Friedrich−Herschbach approach. The molecule
is modeled using geometries and zero-point vibrations from a coupled-cluster level ab initio calculation. The
alignment is achieved by a circularly polarized, quasicontinuous high-intensity laser pulse that intersects the
molecular sample at selected geometries. The molecular ensemble is taken to be at a rotational temperature
of 5 K. We find that even at 1 TW/cm2 there is a very noticeable effect on the diffraction pattern stemming
from the alignment. Moreover, using different laser geometries, it is possible to observe different diffraction
patterns corresponding to specific projections of the molecular geometry onto the Fourier plane of the detector,
making the laser a kind of “optical goniometer.” Predictably, higher alignment laser intensities lead to narrower
orientational distributions, which in turn provide for diffraction patterns with larger modulation depths. We
find, however, that for small diffraction angles (s ≤ 15 Å-1) the effect appears to saturate at an alignment
laser intensity of about 4 TW/cm2. This suggests that there is a window of opportunity where alignment is
very beneficial for extracting information from gas-phase diffraction patterns and where detrimental multiphoton
processes do not yet compromise the interpretation of the molecular structure.