Enhanced ionization of the non-symmetric HeH+ molecule driven by intense ultrashort laser pulses

Abstract

We study enhanced single and double ionizations and enhanced single and double excitations in the nonsymmetric two-electron diatomic molecular ion HeH(+) in an intense ultrashort laser pulse linearly polarized along the internuclear axis (z axis). We solve a three-dimensional time-dependent Schrödinger equation, TDSE, via correlated two-electron ab initio calculations within the fixed-nuclei approximation. A complex scaling method is used for calculation of both single and double ionizations. These nonperturbative processes increase with large internuclear distance R and reach a maximum at some critical distance R(c) and decrease by further increase of R. This enhanced ionization (EI) at R(c) is accompanied by enhanced single and double excitation processes. Furthermore, EI is stronger when the permanent dipole moment of the molecule and the electric field at the peak of the laser pulse are antiparallel than when they are parallel. We predict analytically the R(c) at which the enhancement of all these molecular processes happens in HeH(+) from a simple quasistatic model and investigate the effect of Carrier Envelope Phase on these nonlinear nonperturbative processes.

Heteronuclear Limit of Strong-Field Ionization: Fragmentation of HeH+ by Intense Ultrashort Laser Pulses

“…An estimate of the characteristic time of this stretching motion can be done by the vibrational period associated to the v = 6 − 10 states, which is on the order of 34-100 fs or by the time a corresponding classical particle moves from R = 2 to R= 3.7 a.u., which is ≈12 fs. As a consequence, the ionization rate increases sharply for the stretched molecules [12], which induces molecular vibration and further ionization via the Lochfraß mechanism [25]. This mechanism is corroborated by the eyecatching lack of yield at KER= 8.5 eV (R = 3.1 a.u.)…”

“…On the theory side, the solution of the time-dependent Schrödinger equation (TDSE) with all 9 degrees of freedom necessary to describe HeH + is extremely challenging and unfeasible with current computational resources. Therefore, approximations such as TDSE calculations with reduced dimensionality [12][13][14] or semiclassical approaches [15] are often used.…”

“…near the outer turning point of the initial wave function, 400 nm is predicted to more effectively drive electronic excitation and enhance ionization as compared to 800 nm [12,26]. Note that [12] uses fixed-nuclei approximations. In contrast to their work, we highlight the relevance of vibrational excitation, which is the prerequisite step and is not discussed in Ref.…”

Electron correlation effects in enhanced ionization of diatomic molecules in near-infrared fields

“…Another mechanism explains EI as the strong coupling of charge-resonant states at certain critical internuclear separation which then leads to an enhanced molecular ionization probability [14]. Studies by numerically solving the time-dependent Schrödinger equation (TDSE) show that EI persists in two-electron homo-and heteronuclear molecules [21][22][23][24][25][26]. An accurate description of EI is crucial for the understanding of nuclear kinetic energy release spectra following strong-field-induced dissociative ionization (see, e.g., Ref.…”

Strong field ionization rates simulated with time-dependent configuration interaction and an absorbing potential

“…9,10,34,[47][48][49][50] For H + 2 and H 2 , it has been shown that charge resonance transitions and localization of the electronic wavefunction are responsible for this Charge-Resonance Enhanced Ionization (CREI) at critical internuclear distances. 47,48 Several numerical simulations have been carried out for the ionization of H + 2 as a function of bond length.…”