Charge Migration in HCCI Cations Probed by Strong Field Ionization: Time-Dependent Configuration Interaction and Vibrational Wavepacket Simulations

Abstract

Strong field ionization of neutral iodoacetylene (HCCI) can produce a coherent superposition of the X and A cations and results in charge migration between the CC π orbital and the iodine π-type lone pair. This charge migration causes oscillations in the rate of strong field ionization of the cation to the dication that can be monitored using intense few-cycle probe pulses. The dynamics and strong field ionization of the coherent superposition the X and A states of HCCI + have been modeled by time-dependent configuration interaction (TDCI) simulations. When the nuclei are allowed to move, the electronic wavefunctions need to be multiplied by vibrational wavefunctions. Nuclear motion has been modeled by vibrational packets moving on quadratic approximations to the potential energy surfaces for the X and A states of the cation. The overlap of the vibrational wavepackets decays in about 10−15 fs. Consequently, the oscillations in the strong field ionization decay on the same time scale. A revival of the vibrational overlap and in the oscillations of the strong field ionization is seen at 60−110 fs. TDCI simulations show that the decay and revival of the charge migration can be monitored by strong field ionization with intense 2-and 4-cycle linearly polarized 800 nm pulses. The revival is also seen with 7-cycle pulses.

Tracking Charge Migration with Frequency-Matched Strobo-Spectroscopy

“…Understanding the ultrafast motion of electrons within matter is of critical importance in many areas of science and technology. One example is charge migration − (CM): the coherent motion of a positively charged electron hole along the backbone of a molecule following a localized ionization event, which can be observed on Angstrom spatial scales and attosecond time scales. − CM is a widely studied phenomenon due to its potential for understanding and perhaps steering downstream processes such as chemical reactions, photosynthesis, and photovoltaics via charge-directed reactivity. − Since its discovery in the late 1990s, , the study of CM has flourished, ,− with much of this research performed in recent years. − …”