We investigate the mechanism of enhanced ionization that occurs at a critical internuclear distance [Formula Presented] in the two-electron symmetric linear triatomic molecule [Formula Presented] subjected to an ultrashort, intense laser pulse by solving exactly the time-dependent Schrödinger equation for a one-dimensional model of [Formula Presented] Results of the simulations are analyzed by using three essential adiabatic field states |1〉, |2〉, and |3〉 that are adiabatically connected with the lowest three electronic states [Formula Presented] [Formula Presented] and [Formula Presented] of the field free ion. We give also a simple MO (molecular orbital) picture in terms of these three states to illustrate the important electronic configurations in an intense field. The states |1〉, |2〉, and |3〉 are shown to be composed mainly of the configurations [Formula Presented] [Formula Presented] and [Formula Presented] respectively in the presence of the field. We conclude that the overall level dynamics is governed mainly by transitions at the zero-field energy quasicrossings of these three states. The response of [Formula Presented] to a laser field can be classified into two regimes. In the adiabatic regime [Formula Presented] the electron transfers from one end of the molecule to the other end every half optical cycle thus creating the ionic component [Formula Presented] In the diabatic regime [Formula Presented] internuclear electron transfer is suppressed due to electron repulsion and laser induced localization. In the intermediate [Formula Presented] region, where enhanced ionization occurs, the state |3〉 is most efficiently created by the field-induced nonadiabatic transitions between the states at quasicrossing points. The “quasistatic” laser-induced potential barriers are low enough for the electron to tunnel from the ascending (upper) well, thus confirming the quasistatic model at high intensities. Analytic expressions for the critical distance [Formula Presented] are obtained from this model and collective electron motion is inferred from the detailed time-dependent two-electron distributions.
|Number of pages||1|
|Journal||Physical Review A - Atomic, Molecular, and Optical Physics|
|Publication status||Published - 2001 Jan 1|
ASJC Scopus subject areas
- Atomic and Molecular Physics, and Optics