We investigate the impulsive alignment of acetylene (${\mathrm{C}}_2{\mathrm{H}}_2$) molecules via resonant vibrational excitation using ultrashort infrared laser pulses. Focusing on two vibrational bands, the fundamental mode ${\nu }_3$ at 3 µm and the combination band ${\nu }_1+{\nu }_3$ at 1.5 µm, we compare theoretical predictions with experimental observations. Numerical simulations reveal that excitation of the ${\nu }_3$ band induces a pronounced and persistent planar alignment characteristic of resonant processes, akin to phenomena recently observed in iodine molecules. In contrast, alignment via the ${\nu }_1+{\nu }_3$ band is predominantly governed by nonresonant interactions due to the weaker transition dipole moment, resulting in a negligible resonant contribution. Experimental measurements at 1.5 µm confirm the dominance of nonresonant dynamics. These findings highlight the importance of dipole strength in resonant alignment and support the broader applicability of vibrationally driven alignment strategies in molecular control.

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• Atomic & molecular processes in external fields
• Optical coherence
• Strong electromagnetic field effects
• Ultrafast phenomena