We study laser-induced dissociation of a metastable ${\mathrm{NO}}^{2+}$ ion-beam target into ${\mathrm{N}}^{+}+{\mathrm{O}}^{+}$, focusing on the prominent contribution by molecules breaking parallel to the polarization at high peak laser intensity $(\sim {10}^{15}$ $\mathrm{W}/{\mathrm{cm}}^2)$. Our experimental results and time-dependent Schrödinger equation calculations show that, contrary to commonly held intuition that electronic transitions always prevail, the dominant process underlying this highly aligned dissociation is a multiphoton permanent-dipole transition involving only the electronic ground state and leading to its vibrational continuum. Strong-field permanent-dipole transitions should thus be considered generally, as they may play a significant role in other heteronuclear molecules. Moreover, their role should only grow in importance for longer wavelengths, a trending direction in ultrafast laser studies.

• Received 20 February 2022
• Accepted 21 March 2022

DOI:https://doi.org/10.1103/PhysRevA.105.043101