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It has recently been shown that strong field multiple ionization of water depends on the duration and intensity of the laser pulse. While the polarizability of neutral water is isotropic, the polarizability of the molecular ions can be significant and evolve in time. If the molecular ions spend enough time in the field, dynamic alignment can reorient them and modify the yield of dissociating fragments as a function of angle relative to the polarization of the laser. Unbending motion is one way that the polarizability of the molecular ions increases. Here, we study strong field ionization of water in the long pulse regime where dynamic alignment and unbending are known to contribute at 800 nm, and we tune the laser wavelength to modify coupling between the states of the monocation. A resonance between the X and A states at 660 nm should excite the monocation and initiate unbending motion, but our results cannot be explained without considering the dynamics and structure of the dication and trication. To conduct these measurements, we utilize laser pulses with a duration of 40 fs and central wavelengths of 660 nm, 800 nm, and 1330 nm to multiply-ionize an effusive molecular beam of water. The resulting charged fragments are detected using a velocity map imaging apparatus. Our results provide additional clues about the strong field ionization of water. *M.B., G.A.M., A.J.H., N.P., and P.H.B. were supported by the National Science Foundation. A.J.H. was additionally supported under a Stanford Graduate Fellowship as the 2019 Albion Walter Hewlett Fellow. N.P. was additionally supported by the Hertz Foundation. R.F. was supported by the Department of Energy office of Basic Energy Science, Facilities Division. 

We have observed details of the internal motion and dissociation channels in photoexcited carbon disulfide (CS2) using time-resolved x-ray scattering (TRXS). Photoexcitation of gas-phase CS2 with a 200 nm laser pulse launches oscillatory bending and stretching motion, leading to dissociation of atomic sulfur in under a picosecond. During the first 300 fs following excitation, we observe significant changes in the vibrational frequency as well as some dissociation of the C–S bond, leading to atomic sulfur in the both 1D and 3P states. Beyond 1400 fs, the dissociation is consistent with primarily 3P atomic sulfur dissociation. This channel-resolved measurement of the dissociation time is based on our analysis of the time-windowed dissociation radial velocity distribution, which is measured using the temporal Fourier transform of the TRXS data aided by a Hough transform that extracts the slopes of linear features in an image. The relative strength of the two dissociation channels reflects both their branching ratio and differences in the spread of their dissociation times. Measuring the time-resolved dissociation radial velocity distribution aids the resolution of discrepancies between models for dissociation proposed by prior photoelectron spectroscopy work.