Strong Field Ionization of Water II: Electronic and Nuclear Dynamics En Route to Double Ionization

The Strong Field Ionization (SFI) is an important tool to study molecular dynamics. For a small system as I$_2$, it could be used to map the Wigner distribution of the wave function [1] assuming the pulse is short enough. Usually 10fs is short enough to probe most molecular dynamics as if the nuclear motion is "frozen" in such a short period [2] so the transitions are "vertical transition". Yet our recent experiments on D$_2$O seems to indicate that the story is not that simple. Here we apply the strong field ionization to doubly ionize the deuterated water (D$_2$O) molecule. Using coincidence Velocity Map Imaging (VMI) machine, we get both electrons and ions simultaneously which is recorded using Timepix3 camera [3]. Comparing our momentum resolved D$^+$/D$^+$/O channel and the theory prediction outlined in [4] suggests the 10fs pulse is not a vertical transition. We try to explain such discrepancy between experiment and theory from some known strong field effects like the R-dependent ionization [5]. 

[1] Petersen, C., Peronne, E., Th?gersen, J., Stapelfeldt, H. and Machholm, M., 2004. Control and imaging of interfering wave packets in dissociating I 2 molecules. Physical Review A, 70(3), p.033404.

[2] Sándor, P., Tagliamonti, V., Zhao, A., Rozgonyi, T., Ruckenbauer, M., Marquetand, P. and Weinacht, T., 2016. Strong field molecular ionization in the impulsive limit: Freezing vibrations with short pulses. Physical review letters, 116(6), p.063002.

[3] Zhao, A., van Beuzekom, M., Bouwens, B., Byelov, D., Chakaberia, I., Cheng, C., Maddox, E., Nomerotski, A., Svihra, P., Visser, J. and Vrba, V., 2017. Coincidence velocity map imaging using Tpx3Cam, a time stamping optical camera with 1.5 ns timing resolution. Review of Scientific Instruments, 88(11), p.113104.

[4] Streeter, Z.L., Yip, F.L., Lucchese, R.R., Gervais, B., Rescigno, T.N. and McCurdy, C.W., 2018. Dissociation dynamics of the water dication following one-photon double ionization. I. Theory. Physical Review A, 98(5), p.053429.

[5] Fang, L. and Gibson, G.N., 2008. Strong-field induced vibrational coherence in the ground electronic state of hot I 2. Physical review letters, 100(10), p.103003.