We demonstrate a combined experimental and theoretical study to measure attosecond-resolved resonance-enhanced multiphoton ionization (REMPI) of NO molecules using the phase-locked strong 400-nm and weak 800-nm laser pulses. By performing the time-dependent wave-packet simulation, our results show that a vibrational-dependent REMPI occurs through two intermediate electronic states $A{}^2{\mathrm{\Sigma }}^{+}$ and $B{}^2\mathrm{\Pi }$, from which a molecular wave packet at different internuclear distances results in an ionization time delay up to 630 as. We find that the nonadiabatic coupling between electronic states $A{}^2{\mathrm{\Sigma }}^{+}(\nu =2)$ and $B{}^2\mathrm{\Pi }({\nu }^{\prime }=4)$ plays a crucial role in the angular-dependent phase variations of emitted electrons. This work extends the application of the REMPI technique to visualize the effect of vibrational motions of intermediate resonance states on the strong-field-induced ionization in attosecond timescales.

• Received 15 May 2023
• Accepted 27 July 2023

DOI:https://doi.org/10.1103/PhysRevA.108.023114