The electronic motion inside the molecule is of fundamental importance in determining the formation and fracture of chemical bonds. For more than two decades, many efforts have been done to study the electronic dynamics in laser-matter interactions, aiming at the control over ultrafast reactions. With the recent development of laser techniques and attosecond science, it has become feasible to steer the electron localization in dissociating molecules with the carrier-envelope phase (CEP) stabilized few-cycle laser pulses or the sequential ultraviolet and near-infrared pulses.

In our work, we have theoretically studied the effect of nuclear mass on electron localization in dissociating H$_2$$^+$ and its isotopes subjected to a few-cycle 3-$\mu$m pulse. Our results reveal an anomalous isotopic effect in which the degree of electron-directed reactivity can be even higher for heavier isotopes in the intense midinfrared field. We show, for the first time, the pronounced electron localization can be established through the interferences among the multi-photon coupling channels. Due to the relative enhancement of higher-order coupling channels with growing mass, the interference maxima at different kinetic energy of the spectra gradually become in phase, ultimately resulting in the larger dissociation asymmetries of heavier isotopes. This unexpected isotopic behavior has provided us deep insights into the electronic dynamics in molecular dissociation and the high-order multi-photon coupling channels appear to be an important role in the control over electron-directed reactivity of larger molecules with midinfrared pulses.
This work, published in Optics Express 21, 5107 (2013), was supported by the NNSF of China under Grants No. 10904045, No. 11234004, and No. 60925021, the 973 Program of China under Grant No. 2011CB808103, and the Doctoral Fund of Ministry of Education of China under Grant No. 20100142110047. 
Figure 1 The asymmetry parameter as a function of the CEP and the kinetic energy for (a) H2+, (b) D2+, and (c) T2+ in the 3000-nm pulse.