Measuring attosecond time-delays between dissociating vibrational states of D$_2^+$ using a two-color laser field*

There is considerable interest in studying attosecond time-delays in the photoionization of neighboring electronic states of atomic and more complex targets. The underlying assumption of that work is that electron dynamics are responsible for such short delays, since they match the natural electronic timescale. Recent theoretical work has shown that the two-color dissociation probability of adjacent vibrational states in the HeH$^+$ molecule exhibit time-delays of tens of attoseconds. Since electronic excitation is negligible in HeH$^+$ for the considered laser parameters, this demonstrates that attosecond delays occur for purely nuclear motion. Here, we present an analogous experiment on a D$_2^+$ ion beam, where attosecond time-delays are observed using an intense two-color (800/400-nm) laser field. In the two-color field, interfering pathways ending in opposite parity states result in a spatial asymmetry with respect to the laser polarization. By comparing the phase shifts of the spatial asymmetry parameter between the $v=7$ and $v=8$ vibrational states of the $1s\sigma_g$, we observe a $53$-as delay.